Back- and front-side texturing for light-management in perovskite / silicon-heterojunction tandem solar cells

The perovskite / silicon-heterojunction (SHJ) tandem solar cell can theoretically overcome the efficiencies of the single junction solar cells with experimental results not far behind. Here, we use optical simulations to analyze the potential of such currently feasible monolithic perovskite / SHJ tandem devices. We consider three different device designs in the optical simulations: planar device, device built on back-side textured Si wafer, and device with textured UV Nanoimprint Lithography light management foil. For each of these three designs, the current matching point is simulated to evaluate device efficiencies. While the device with back-side textured Si wafer causes light trapping and therefore enhanced photocurrent generation for longer wavelengths, the anti-reflection foils prove to be overall more efficient as the foil significantly reduces the reflection in almost full wavelength range

21.6%-efficient monolithic perovskite/Cu(In,Ga)Se2 tandem solar cells with thin conformal hole transport layers for integration on rough bottom cell surfaces

Perovskite-based tandem solar cells can increase the power conversion efficiency (PCE) of conventional single-junction photovoltaic devices. Here, we present monolithic perovskite/CIGSe tandem solar cells with a perovskite top cell fabricated directly on an as-grown, rough CIGSe bottom cell. To prevent potential shunting due to the rough CIGSe surface, a thin NiOx layer is conformally deposited via atomic layer deposition on the front contact of the CIGSe bottom cell. The performance is further improved by an additional layer of the polymer PTAA at the NiOx/perovskite interface. This hole transport bilayer enables a 21.6% stabilized PCE of the tandem device at ∼0.8 cm2 active area. We use TEM/EDX measurements to investigate the deposition uniformity and conformality of the NiOx and PTAA layers. By absolute photoluminescence measurements, the contribution of the individual subcells to the tandem VOC is determined, revealing that further fine-tuning of the recombination layers might improve the tandem VOC. Finally, on the basis of the obtained results, we give guidelines to improve monolithic perovskite/CIGSe tandems toward predicted PCE estimates above 30%.BMBF, 03SF0540, Nachwuchsgruppe MeSa-Zuma: Entwicklung von spektral optimierten, hocheffizienten und langzeitstabilen Perowskit/Silizium Tandem SolarzellenBMWi, 0324095D, Verbundvorhaben: speedCIGS - Rechnerunterstützte Optimierung des CIGS-Depositionsprozesses in der industriellen Umsetzung; Teilvorhaben: Alkalibehandlung der CIGS Absorberoberfläche und monolithisch integrierte Tandem Zelle (p-TCM)BMWi, 0324076D, Verbundvorhaben: EFFCIS - Effizienzoptimierung von CIS-basierten Dünnschichtsolarzellen und -modulen; Teilvorhaben: Elektronenstrukturrechnungen zum Einfluss von Puffermaterialien auf die Eigenschaften des Cu(ln,Ga)(S,Se)2 Absorber

Monolithic perovskite/silicon tandem solar cell with >29% efficiency by enhanced hole extraction

Tandem solar cells that pair silicon with a metal halide perovskite are a promising option for surpassing the single-cell efficiency limit. We report a monolithic perovskite/silicon tandem with a certified power conversion efficiency of 29.15%. The perovskite absorber, with a bandgap of 1.68 electron volts, remained phase-stable under illumination through a combination of fast hole extraction and minimized nonradiative recombination at the hole-selective interface. These features were made possible by a self-assembled, methyl-substituted carbazole monolayer as the hole-selective layer in the perovskite cell. The accelerated hole extraction was linked to a low ideality factor of 1.26 and single-junction fill factors of up to 84%, while enabling a tandem open-circuit voltage of as high as 1.92 volts. In air, without encapsulation, a tandem retained 95% of its initial efficiency after 300 hours of operation.BMBF, 03SF0540, Nachwuchsgruppe MeSa-Zuma: Entwicklung von spektral optimierten, hocheffizienten und langzeitstabilen Perowskit/Silizium Tandem SolarzellenBMWi, 0324288C, Verbundvorhaben: ProTandem - Demonstration der Produktionstauglichkeit von Perowskit-Silizium Tandemsolarzellen; Teilvorhaben: Entwicklung von Kontaktschichten für die Silizium-Heterojunction BottomzelleEC/H2020/763977/EU/Perovskite Thin-film Photovoltaics (PERTPV)/PERTPVDFG, 423749265, Identifizierung und Unterdrückung von Grenzflächenrekombination für hocheffiziente Perowskit-SolarzellenDFG, 402726906, SPP 2196: Perowskit-Halbleiter: Von fundamentalen Eigenschaften zur Anwendun

Advantages of modern combinations in road and railway transportation

Slovenija postaja s svojo geografsko lego ključnega pomena za transport, saj naj bi s svojo infrastrukturo omogočala enakomeren pretok blaga, brez nepotrebnih negativnih učinkov na okolico. Živimo v času, ko smo priča številnim gospodarskim spremembam, hitremu gospodarskemu razvoju in tehnološkemu napredku na prav vseh področjih človekovega delovanja. Izrazit tehnološki napredek je opazen tudi na področju komunikacij, informacijske tehnologije in prometa. Naraščajo mednarodna menjava, intenzivno mednarodno povezovanje, globalizacija ter prenos upravljanja podjetij tudi preko državnih meja. Premagovanje prostora in časa je primarna potreba vsake sodobne družbe. Čedalje pomembnejše je dovolj celostno upravljanje toka dobrin in informacij, od proizvajalca do končnega potrošnika, od mesta nabave surovin (od izvora blaga in storitev) do mesta prodaje končnih proizvodov kupcem (do ponora blaga in storitev). Temeljno načelo logistike je, da mora proizvod priti ob pravem času, na pravo mesto, v zahtevani količini in kakovosti. Pri tem je potrebno čimbolj zadovoljiti potrošnikove potrebe in želje ter doseči čim manjše stroške. Geografska lega (majhne) Slovenije in v njej udeleženih raznovrstnih poslovnih subjektov mora doprinašati koristi ugodenega položaja in zaradi njega pospešiti razvoj transporta. Vse prevečkrat se namreč zgodi, da zaradi nepremišljenih potez ostajamo nekonkurenčni znotraj Evropske unije. Transport je sicer ključni dejavnik moderne ekonomske družbe, a se še zmeraj pojavljajo številna protislovja, kot na primer težnja po vse večji mobilnosti na eni strani, na drugi pa se pričakuje manj zastojev in slabih izvedb transporta. Ugotovljeno je, da je ob tem fenomenu nemogoče v nedogled povečevati zmogljivosti obstoječe infrastrukture, saj lahko to pomeni, da bomo uničili večino naše bivalne pokrajine. Odgovor na te težnje mora biti v čim večji optimizaciji transporta, kar zahteva razvoj ter povečevanje zmogljivosti in organizacije prevoza blaga. Moderne smernice transporta morajo biti prilagojene ekonomskemu in socialnemu vidiku ob tem, pa morajo odgovoriti na vsa vprašanje, ki se pojavljajo v zvezi z ekologijo, tj. varovanjem okolja in zagotavljanjem želene stopnje kakovosti življenja.With its geographic structure, Slovenia is becoming of key importance for transport, since its infrastructure is supposed to enable an even flow of goods, without any unnecessary negative effects on the environment. We are living in a time of continuous economic changes, fast economic and technological development in all fields of human activity. Prominent technological progress is also visible in the fields of communications, information technology and traffic. International trade, connections and globalization are growing, as well as cross-border management of companies. Overcoming the time and space is a primary need of each modern society. Integrated control of information and goods flow is more and more important, from manufacturer to final customer, from the place of purchase of raw products (source of goods and services) to the place of final sales (sink of goods and services). The basic principle of logistics is that the product must be delivered at the right time to the right place in required quantity and quality, taking into account to fulfill the consumers’ needs and wishes to the maximum and acquire the lowest possible costs. The geographic position of (small) Slovenia and the involved various economic subjects must bring benefits from the advantageous position and accelerate the development of transport. It happens way too often that we are not competitive inside the European Union due to ill-advised moves. While the transport is the key element of modern economic society, there are still great contradictions in this field, as for example the tendency for greater mobility on one side and expectation of less traffic jams and bad transport implementations on the other side. It is established that this phenomenon makes it impossible to indefinitely enlarge the capacities of existing structure, since this could signify, that we will destroy most of our living landscape. The answer to this problem must be in greater optimization of transport, which requires development and larger capacity and organization of goods transport. Modern directions of transport must be adapted to economical and social aspect and also give an answer to all questions concerning ecology, such as environment protection and assurance of desired level of quality of living

Herstellung und Charakterisierung von Nanotexturen für Lichtmanagement in Photovoltaik- und Optoelektronikgeräten

Light management is an important aspect of photovoltaics to assure efficient exploitation of solar energy and improve the efficiency of solar cells. Efficient light management is based on anti-reflection and light scattering. The former results in increased light in-coupling, and the latter prolongs the optical path in the active layer of a solar cell; consequently, the conversion efficiency increases. Both effects are usually induced by textured surfaces, either within the device structure or on top of the device. In the doctoral dissertation, we focus on fabrication and characterization of textured light management layers. The created light management (LM) foil is then applied on top of perovskite solar cells to enhance the perofromance and analyze the improvements in the fabricated devices. The Ultra-Violet Nanoimprint Lithography (UV NIL) is used to create the textured LM foils. It is a novel approach for replicating textured surfaces. The process is cost-effective, simple and faster compared to other texturization techniques. In the replication process, the texture surface from the master is transferred to the replica with the help of the intermediate stamp and the UV sensitive lacquers coated on the substrates. We present the replication process and thoroughly characterize the created replicas using surface morphology and transmittance measurements. Good transfer fidelity and moderate thermal stability up to 200 °C were obtained. During the thermal stability test the samples that were exposed to high temperature (200 °C) for a longer time (>30 min) turned slightly yellow. The yellowing effect resulted in diminished total and diffuse transmittance of light for the wavelengths below 500 nm. Similar effect is also observed during the outdoor testing where different configurations were tested, some samples were placed on a white and some on a black surface. After three-month exposure to outdoor environmental conditions the samples turned yellow. Samples on black surface heated more and the yellowing effect was severer than for the samples on white surface. Additionally, the lacquer slightly melted which is confirmed by lower σRMS values. This shows that replication lacquers with more stable chemical composition are needed for use in real outdoor applications. If the LM foil is used inside the device, an additional conductive layer of transparent conductive oxide (TCO) has to be deposited on top of the LM foil to form electrical contact as the UV NIL lacquers are non-conductive. In our case, a gallium doped ITO (GITO) is used as a TCO. The successfulness of the deposition is confirmed by sheet resistance, optical (transmission) and surface morphology measurements. To fulfill their role, the created replicas should preserve the light scattering properties of the master. For the light scattering characterization, a novel camera-based system is developed. It enables measurements of the spatial angular distribution function (3D ADF) of scattered or emitted light using a digital camera. 3D ADF is determined from the digital image captured from a flat screen. We present two solutions. The first uses a reflective screen and a lens to broaden the angular range. The second uses a transmissive screen positioned at 45°, enabling measurements of all the polar angles. With the developed camera-based systems we can quantify transmitted or reflected light scattered by textured samples or emitted light from light sources in a few seconds. In the dissertation, both setups are described, and main transformations of the acquired digital image to obtain the 3D ADF are explained. The systems are validated on randomly nanotextured transparent samples and a periodically textured non-transparent sample. Good matching is obtained with rigorous simulations, and measurement results carried out with the conventional goniometric angular resolved scattering system. The system with the transmissive screen is used to characterize the created replicas. To test the functionality of the created LM foils in a real application, inorganic-organic perovskites that have proven to be an effective class of materials for fabricating efficient solar cells are used. We apply an LM foil created by UV NIL on the glass side of an inverted (p-i-n) perovskite solar cell with 16.3% efficiency. The obtained 1 mA cm 2 increase in the short-circuit current density translates to a relative improvement of 5% in cell performance, which results in a power conversion efficiency of 17.1%. To support the experimental findings, optical 3D simulations based on experimentally obtained parameters are used. A good match between the simulated and experimental data is obtained, validating the model. Optical simulations reveal that the main improvement in device performance is due to a reduction in total reflection and that relative improvement in the short-circuit current of up to 10% is possible for large-area devices. The optical model is also used to analyze the potential of monolithic perovskite/silicon-heterojunction tandem devices that can theoretically overcome the efficiencies of the single junction solar cells. We consider four different device designs in the optical simulations: the planar device, the device built on back- and both-side textured Si wafer, and the device with the textured LM foil. For each of these four designs, the current matching point is simulated to evaluate device efficiencies. The results reveal that the device built on a both-side textured silicon wafer, which is the best performing configuration, can reach 15% relative higher efficiency than planar device. The obtained results show the potential of LM foils for improving the device performance of perovskite solar cells and pave the way for further use of optical simulations in perovskite single junction or tandem solar cells.Lichtmanagement ist ein wichtiger Aspekt der Photovoltaik, um eine effiziente Nutzung der Solarenergie zu gewährleisten und die Effizienz von Solarzellen zu verbessern. Ein effizientes Lichtmanagement basiert auf Antireflexion und Lichtstreuung. Erstere verringert Verluste durch Reflexion des einfallenden Lichtes. Letztere verlängert den optischen Weg in der aktiven Schicht einer Solarzelle und erhöht damit die Absoprtion des einfallenden Sonnenlichtes. Dadurch wird der Wirkungsgrad erhöht. Beide Effekte werden üblicherweise durch strukturierte Oberflächen entweder innerhalb des Schichtstapels oder auf der Oberseite des Bauteils eingebracht. Diese Dissertation konzentriert sich auf die Herstellung und Charakterisierung von texturierten Schichten zur Verbesserung des Lichtmanagements. Dazu wird eine texturierte Lichtmanagementfolie (LM-Folie) mit passendem Brechungsindex auf Perovskit-Solarzellen aufgetragen, um eine Verbesserungen in den gefertigten Solarzellen zu ermöglichen und diese anschließend im Detail zu analysieren. Zur Herstellung der texturierten LM-Folien wird Ultraviolett-Nanoimprint-Lithographie (UV NIL) verwendet. Es ist ein neuartiger Ansatz für die Replikation von texturierten Oberflächen. Der Prozess ist kostengünstig, einfach und schneller als andere Texturierungstechniken. Hierbei wird die Texturoberfläche von einem Master auf ein Duplikat mit Hilfe eines Zwischenstempels übertragen und UV-empfindliche Lacke auf die Substrate aufgetragen. Wir stellen den Replikationsprozess vor und charakterisieren die erzeugten Duplikate mit Oberflächenmorphologie und Transmissionsmessungen. Dabei konnte eine hohe Reproduzierbarkeit der zu transferierenden Oberfläche und eine moderate thermische Stabilität bis zu 200 °C realisiert werden. Während des thermischen Stabilitätstests verfärbten sich die Proben, die für eine längere Zeit (> 30 min) einer hohen Temperatur (200 °C) ausgesetzt waren, gelblich. Der Vergilbungeffekt führte zu einer verminderten Gesamt- und diffusen Durchlässigkeit für Licht mit Wellenlängen unter 500 nm. Ein ähnlicher Effekt wird auch während der Outdoor-Tests beobachtet. Hierbei wurden verschiedene Konfigurationen getestet. Einige Proben wurden auf einer weißen und einige auf einer schwarzen Oberfläche platziert. Nach dreimonatiger Exposition gegenüber den Umgebungsbedingungen verfärbten sich die Proben gelb. Proben auf schwarzer Oberfläche erhitzten sich stärker und die Vergilbung war stärker als jene der Proben auf weißer Oberfläche. Zusätzlich kam es zu einem leichten Schmelzen des Lacks, was durch niedrigere σRMS-Werte bestätigt werden konnte. Dies zeigt, dass Replikationslacke mit einer stabileren chemischen Zusammensetzung für den Einsatz in realen Anwendungen benötigt werden. Wenn die LM-Folie innerhalb des Gerätes verwendet wird, muss eine zusätzliche leitfähige Schicht aus einem transparenten leitfähigen Oxid (TCO) auf der Oberseite der LM-Folie abgeschieden werden, um einen elektrischen Kontakt zu bilden, da die UV-NIL-Lacke nicht leitend sind. In unserem Fall wird ein Gallium dotiertes ITO (GITO) als TCO verwendet. Der Erfolg der Ablagerung wird durch Messungen des Flächenwiderstands, der Oberflächenmorphologie und durch optische Messungen (Transmission) bestätigt. Eine für die Anwendung wichtige Grundvoraussetzung ist, dass die erzeugten Repliken die genaue Oberflächentextur und damit die Lichtstreuungseigenschaften des Masters bewahren. Für die Messungen der Lichtstreuung wird ein neuartiges kamerabasiertes System entwickelt. Es ermöglicht die Bestimmung der räumlichen Winkelverteilungsfunktion (3D ADF) von gestreutem oder emittiertem Licht mit einer Digitalkamera. Die 3D ADF wird aus dem digitalen Bild ermittelt das auf einem Schirm aufgenommen wurde. Wir stellen zwei Lösungen vor: Die erste verwendet einen reflektierenden Bildschirm und eine Linse, um den Winkelbereich zu erweitern. Die zweite verwendet einen lichtdurchlässigen Schirm, der bei 45 ° positioniert ist und die Messungen aller Polarwinkel ermöglicht. Mit diesem System können wir sowohl transmittiertes oder reflektiertes Licht, gestreut von strukturierten Proben, als auch direktes Licht von Lichtquellen in wenigen Sekunden quantifizieren. In dieser Dissertation werden beide Setups beschrieben. Die Transformationen des erfassten digitalen Bildes zur Bestimmung des 3D ADF werden erläutert. Die Systeme werden mithilfe einer zufällig nanotexturierten transparenten Probe und einer periodisch strukturierten, nicht transparenten Probe validiert. Eine gute Übereinstimmung wird mit rigorosen Simulationen und Messergebnissen erzielt, die mit einem herkömmlichen goniometrischen, winkelabhängig aufgelösten Streusystem durchgeführt werden. Das System mit dem lichtdurchlässigen Bildschirm wird verwendet, um die erstellten Duplikate zu charakterisieren. Um die Funktionalität der erzeugten LM-Folien in einer realen Anwendung zu testen, werden anorganisch-organische Perovskite verwendet, die sich als wirksame Materialklasse für die Herstellung effizienter Solarzellen erwiesen haben. Wir prozessieren eine mit UV NIL hergestellte LM-Folie auf der Glasseite einer invertierten (p-i-n) Perovskit-Solarzelle mit 16,3% Wirkungsgrad. Durch die LM-Folie erhöht sich der Kurzschlussstroms um 1mA/cm² was zu einer beachtlichen relativen Verbesserung des Wirkungsgrades von 5% auf einen Gesamtwirkungsgsrad von 17,1% führt. Zur Unterstützung der experimentellen Ergebnisse werden optische 3D-Simulationen, die auf experimentell gewonnenen Parametern basieren, verwendet. Es wird eine gute Übereinstimmung zwischen den simulierten und experimentellen Daten erhalten, die das Modell validiert. Die optischen Simulationen zeigen, dass die wesentliche Verbesserung der Bauteileffizienz auf eine Verringerung der Totalreflexion zurückzuführen ist. Für großflächige Solarzellen ist eine relative Verbesserung des Kurzschlussstroms von bis zu 10% möglich. Das optische Modell wird auch verwendet, um das Potential von monolithischen Perovskit/Silizium-Heterojunction-Tandemgeräten zu analysieren, welche theoretisch die Effizienz der Einzelsolarzellee überwinden kann. Wir betrachten vier verschiedene Bauweisen in den optischen Simulationen: planar Solarzellen, Zellen auf rück- oder beidseitig texturierten Si Wafer, und planare Zellen mit einer texturierten LM-Folie auf der Frontseite. Für jede dieser vier Designs wird das Stromgleichgewicht zwischen den beiden Subzellen simuliert, um deren Effizienz zu bewerten. Dabei erzielt die Zelle auf dem beidseitig strukturierten Silizium-Wafer die bestmöglichen Ergebnisse. Eine relative Steigerung der Effizienz um 15% im Vergleich zur planaren Solarzelle kann erreicht werden. Des Weiteren wird das Potenzial von LM-Folien zur Verbesserung der Bauteileffizienz von Perovskit-Solarzellen gezeigt und der Weg für den weiteren Einsatz optischer Simulationen in Perovskit-Einzel- oder Tandem-Solarzellen geebnet

FABRICATION AND CHARACTERIZATION OF NANOTEXTURES FOR LIGHT MANAGEMENT IN PHOTOVOLTAIC AND OPTOELECTRONIC DEVICES

Za zmanjševanje onesnaževanja okolja in omejitev globalnega segrevanja postajajo obnovljivi viri energije vedno pomembnejši. Še posebej svetlo prihodnost ima fotovoltaika, saj je sonce neusahljiv in brezplačen vir energije, ki je dostopen na celotni zemeljski obli. V primerjavi z ostalimi viri energije pridobivanje elektrike iz sončne energije ne povzroča nastajanja izpušnih plinov, ogljični odtis pa je tudi z vključeno proizvodnjo sončnih modulov vsaj dvajsetkrat manjši v primerjavi s fosilnimi gorivi. Optimizacija proizvodnih procesov je tudi znižala energijsko vračilno dobo sončnih elektrarn (PV sistemov), ki je za osrednjo Evropo padla na dve leti za polikristalne silicijeve module in tudi pod dve leti za tankoplastne sončne celice. Celo Kitajska, eden izmed največjih onesnaževalcev na svetu, je prepoznala potrebo po čistejšem okolju. Tako je poleg vodilne vloge v proizvodnji sončnih fotonapetostnih modulov, prevzela tudi vlogo največjega proizvajalca elektrike iz sončne energije. Njen pospešen vstop na fotovoltaični trg je povzročil drastičen padec cen in eksponentno rast kumulativne nameščene moči po svetu. V zadnjem letu smo v svetovnem merilu namestili za 70 GW sončnih elektrarn, skupna moč pa je presegla 300 GW. Potencial in prednosti fotovoltaike jo uvrščajo med najpomembnejše trajnostne energetske tehnologije na področju obnovljivih virov in tudi v energetiki nasploh. Osnovni fotonapetostni gradnik je polprevodniška sončna celica. Lastnosti polprevodniškega materiala, predvsem energijska reža, so tiste, ki najbolj vplivajo na učinkovitost pretvorbe sončne celice. Za enospojne sončne celice je teoretična limita (Shockley-Queisser limita) pri standardnih testnih pogojih 33,7 % za energijsko režo 1,34 eV. Na podlagi polprevodnika ločimo več tipov sončnih celic. Najpogostejše so kristalne silicijeve sončne celice (prva generacija), ki dosegajo visoko učinkovitost pretvorbe (do 26,3 %) in največji tržni delež (> 86 %) na svetovnem trgu. Druga generacija so tankoplastne sončne celice, kjer je aktivna plast debela le par mikrometrov, v primerjavi s 150 ali več μm pri kristalnih silicijevih sončnih celicah. Popularnost tankoplastnih sončnih celic temelji na pričakovanih nižjih stroških izdelave. Zaradi tanjših plasti potrebujemo manj materiala, proizvodni stroški pa so zaradi nizkotemperaturnih procesov nižji in energetsko učinkovitejši. Tipična predstavnika sta CIGS in CdTe, ki sta dosegla tudi masovno industrijsko proizvodnjo. Sončne celice tretje generacije (organske, elektrokemijske, perovskitne) obetajo še nižje proizvodne stroške, a industrijske proizvodnje še niso dosegle. So pa v zadnjem času v znanstveni sferi veliko pozornosti pritegnile perovskitne sončne celice, saj so v le nekaj letih raziskovanja dosegle učinkovitost pretvorbe do 22,1 %, kar je najhitrejši porast do sedaj. Kljub nizkim stroškom proizvodnje in visokim učinkovitostim pretvorbe, pa perovskitne sončne celice vseeno čaka še dolga pot. Predvsem stabilnost in majhna dimenzija do sedaj izdelanih celic predstavljata glavni oviri do množične proizvodnje, a hiter razvoj in obsežne raziskave dajejo upanje na industrijsko proizvodnjo ali primernost za nišne aplikacije. Upravljanje s svetlobo v tankoplastnih sončnih celicah Tankoplastne sončne celice predstavljajo nizkocenovno alternativo običajnim kristalnim silicijevim sončnim celicam, saj so za njihovo izdelavo potrebne nižje temperature, porabi se manj materiala, izdelamo pa lahko celo upogljive celice. V primerjavi s kristalnimi silicijevimi sončnimi celicami so tankoplastne tanjše, kar se v splošnem lahko odrazi v manjši absorpciji svetlobe. Ker je učinkovitost pretvorbe sončnih celic v veliki meri odvisna od absorpcije v aktivni plasti, je za povečanje absorpcije v tanjših absorpcijskih plasteh potrebno skrbno upravljanje svetlobe. Ena izmed najuspešnejših tehnik povečanja absorpcije svetlobe v tankoplastnih sončnih celicah je teksturiranje površine, bodisi na zgornji ali spodnji plasti celice. Teksturirane površine z nanometrsko ali mikrometrsko hrapavastjo povzročajo protiodbojni efekt ali sipanje svetlobe (velikost posameznih struktur enaka ali večja valovni dolžini), kar podaljša optično pot v aktivni plasti. S tem povečamo svetlobno generirani tok celice, in če se ne spremenijo električne lastnosti (napetost odprtih sponk VOC in polnilni faktor FF), tudi učinkovitost pretvorbe. Teksturirane plasti lahko vpeljemo na ali pa v strukturo sončne celice. Lahko na sprednjo stran stekla v superstrat konfiguraciji pritrdimo teksturirano folijo za upravljanje s svetlobo (LM folija) ter s tem zmanjšamo odbojnost in povzročimo sipanje svetlobe. Lahko pa teksture vpeljemo znotraj strukture. V tem primeru so teksturirane površine prozorni prevodni oksidi (TCO, nanešen na steklo v superstrat konfiguraciji) ali teksturirani substrati (teksturirani zadnji odbojnik na plastični ali kovinski foliji), lahko pa v strukturo vključimo tudi dodatne plasti. Za obetaven način vpeljave želenih tekstur v sončne celice se je v zadnjih letih izkazala tehnologija vtisa vnaprej pripravljenih nanostruktur v prozorne in na temperaturo odporne lake. Ena izmed takih replikacijskih tehnik je UV nanovtisna litografija (UV NIL). Vzorci (teksture) so narejeni z mehansko deformacijo viskoznih polimerov (lakov), v katere vtisnemo teksturirani kalup, čemur sledi strjevanje laka z UV svetlobo (UV NIL). V kombinaciji z nanosom TCO na vtisnjeno plast se lahko izognemo dragi izdelavi TCO z naravno ali z dodatno obdelavo dobljeno teksturo. S procesom UV NIL prenesemo hrapavost površine s kalupa na repliko, pri čemer se ohrani morfologija kalupa in posledično sipanje svetlobe. Sipano svetlobo lahko nato karakteriziramo s kotno odvisno spektroskopijo (ARS), ki nam omogoča določiti funkcijo kotne porazdelitve (ADF) prepuščene in odbite sipane svetlobe – kako je svetloba sipana pod različnimi koti. Tipično določimo ADF z goniometričnimi sistemi, ki pa so počasni in merijo odziv le v eni ravnini (1D). Primernejši so sistemi s kamero, kjer sipano svetlobo projiciramo na zaslon in jo nato zajamemo s kamero. To nam omogoča hitrejšo in popolnejšo analizo sipane svetlobe v 3D prostoru. V doktorski disertaciji smo se posvetili izdelavi in karakterizaciji plasti za upravljanje s svetlobo. Plasti smo izdelali s procesom UV NIL za replikacijo teksturiranih površin. Izdelane replike smo testirali in karakterizirali, med drugim tudi s sistemom za merjenje sipane svetlobe. V ta namen smo postavili dva sistema, enega z refleksijskim in enega s transmisijskim zaslonom. Delovanje in potencialne izboljšave z uporabo LM folije smo preverili na primeru perovskitnih sončnih celic. Delovanje brez in z LM folijo smo analizirali tako eksperimentalno kot tudi teoretično z optičnimi simulacijami.Light management is an important aspect of photovoltaics to assure efficient exploitation of solar energy and improve the efficiency of solar cells. Efficient light management is based on anti-reflection and light scattering. The former results in increased light in-coupling, and the latter prolongs the optical path in the active layer of a solar cellconsequently, the conversion efficiency increases. Both effects are usually induced by textured surfaces, either within the device structure or on top of the device. In the doctoral dissertation, we focus on fabrication and characterization of textured light management layers. The created light management (LM) foil is then applied on top of perovskite solar cells to enhance the perofromance and analyze the improvements in the fabricated devices. The Ultra-violet Nanoimprint Lithography (UV NIL) is used to create the textured LM foils. It is a novel approach for replicating textured surfaces. The process is cost-effective, simple and faster compared to other texturization techniques. In the replication process, the texture surface from the master is transferred to the replica with the help of the intermediate stamp and the UV sensitive lacquers coated on the substrates. We present the replication process and thoroughly characterize the created replicas using surface morphology and transmittance measurements. Good transfer fidelity and moderate thermal stability up to 200 °C were obtained. During the thermal stability test the samples that were exposed to high temperature (200 °C) for a longer time (>30 min) turned slightly yellow. The yellowing effect resulted in diminished total and diffuse transmittance of light for the wavelengths below 500 nm. Similar effect is also observed during the outdoor testing where different configurations were tested, some samples were placed on a white and some on a black surface. After three-month exposure to outdoor environmental conditions the samples turned yellow. Samples on black surface heated more and the yellowing effect was severer than for the samples on white surface. Additionally, the lacquer slightly melted which is confirmed by lower σRMS values. This shows that replication lacquers with more stable chemical composition are needed for use in real outdoor applications. If the LM foil is used inside the device, an additional conductive layer of transparent conductive oxide (TCO) has to be deposited on top of the LM foil to form electrical contact as the UV NIL lacquers are non-conductive. In our case, a gallium doped ITO (GITO) is used as a TCO. The successfulness of the deposition is confirmed by sheet resistance, optical (transmission) and surface morphology measurements. To fulfill their role, the created replicas should preserve the light scattering properties of the master. For the light scattering characterization, a novel camera-based system is developed. It enables measurements of the spatial angular distribution function (3D ADF) of scattered or emitted light using a digital camera. 3D ADF is determined from the digital image captured from a flat screen. We present two solutions. The first uses a reflective screen and a lens to broaden the angular range. The second uses a transmissive screen positioned at 45°, enabling measurements of all the polar angles. With the developed camera-based systems we can quantify transmitted or reflected light scattered by textured samples or emitted light from light sources in a few seconds. In the dissertation, both setups are described, and main transformations of the acquired digital image to obtain the 3D ADF are explained. The systems are validated on randomly nanotextured transparent samples and a periodically textured non-transparent sample. Good matching is obtained with rigorous simulations, and measurement results carried out with the conventional goniometric angular resolved scattering system. The system with the transmissive screen is used to characterize the created replicas. To test the functionality of the created LM foils in a real application, inorganic-organic perovskites that have proven to be an effective class of materials for fabricating efficient solar cells are used. We apply an LM foil created by UV NIL on the glass side of an inverted (p-i-n) perovskite solar cell with 16.3% efficiency. The obtained 1 mA cm-2 increase in the short-circuit current translates to a relative improvement of 5% in cell performance, which results in a power conversion efficiency of 17.1%. To support the experimental findings, optical 3D simulations based on experimentally obtained parameters are used. A good match between the simulated and experimental data is obtained, validating the model. Optical simulations reveal that the main improvement in device performance is due to a reduction in total reflection and that relative improvement in the short-circuit current of up to 10% is possible for large-area devices. The optical model is also used to analyze the potential of monolithic perovskite/silicon-heterojunction tandem devices that can theoretically overcome the efficiencies of the single junction solar cells. We consider four different device designs in the optical simulations: the planar device, the device built on back- and both-side textured Si wafer, and the device with the textured LM foil. For each of these four designs, the current matching point is simulated to evaluate device efficiencies. The results reveal that the device built on a both-side textured silicon wafer, which is the best performing configuration, can reach 15% relative higher efficiency than planar device. The obtained results show the potential of LM foils for improving the device performance of perovskite solar cells and pave the way for further use of optical simulations in perovskite single junction or tandem solar cells

The state and development of competencies of employees in wood based production

The great changes in business environment, rapid technological development and different approaches to work execution demand from employees in industry, including woodworking, to constantly develop their capabilities and widen their knowledge. Education and training are key parts of development of each employee, through which he can gain new knowledge. It is the key to ensuring their competencies for the job, which in turn leads to greater competitiveness of the companies. The objective of the research was to assess the level of competencies for different profiles of employees in wood industry production and to determine the effect of systematic training on the reduction of deficits in competencies. We have established that the biggest deficits in competencies prior to training were in the fields of development, quality management and control, use of computer tools and programming and management of CNC technologies. It can be concluded that the state of competencies of production workers in wood industry is good. Particularly notable is the positive effect of systematic training on the improvement of their competencies, as there was a significant progress of almost all competencies (by 51.8% on average)

A simulation study of temperature effects on performance parameters of silicon heterojunction solar cells with different ITO/a-Si:H selective contacts

Effects of temperature variation on the performance of silicon heterojunction solar cells are studied using opto-electrical simulations. It is shown that the low-temperature cell efficiency is determined by the fill factor, while at high temperatures it depends on the open-circuit voltage. Simulations revealed that the low-temperature drop in the fill factor is caused by poor tunnelling, in particular at the ITO/p-a-Si:H heterojunction. The authors link this drop in fill factor to a low maximum-power-point voltage and show how poor tunnelling is reflected in the charge redistribution determining the device voltage. The effect of the contact work function on temperature behaviour of efficiency by varying the electron affinity of ITO layers has been demonstrated. It was also demonstrated that increasing the electron affinity of ITO on the p-side minimises the work function mismatch, leading to significant improvements in efficiency, especially at low temperatures, while optimisation on the n-side results in maginal improvements over the entire temperature range. In addition to the cumulative effects of the temperature-dependent parameters, their individual contributions to the efficiency were also investigated. Moreover, it was presented that the thermal energy (kT) determines the efficiency temperature behaviour, while other parameters play only a minor role. This paper shows how temperature variations affect device performance parameters