Elektrolyytin puhdistamisen vaikutukset väriaineaurinkokennojen suorituskykyyn ja pitkän aikavälin stabiiliuteen

The two main objectives of this thesis were to study if performance or long-term stability of dye solar cells increase as a result of electrolyte material purification. Not only the combined effect of the purification of all the electrolyte materials has been examined but also the effect of the purification of each compound has been compared. Furthermore, the specific reasons for cell degradation have been investigated where possible. The overall degradation rate of the test solar cells during the aging test was faster than expected and thus the origin of this fast aging formed as the third main research question. Ultraviolet light was detected to be a very likely reason for the fast degradation and thus, additionally the effect of ultraviolet light on the cell aging has been discussed. The secondary object of this study was to determine the proper procedures for performing long aging studies in the future. This task included the assessment of useful tests and the effects of unavoidably varying light intensity during the aging tests. Also statistical tests were introduced to the analysis of the results of the aging studies. This study showed that the purification of electrolyte solvent does not affect the initial performance of the dye solar cells but increases the cell lifetime. The other electrolyte components were not detected to have any statistically significant effect on either cell lifetime or initial performance. The aging mechanism was discovered to be electrolyte bleaching, i.e. the consumption of charge carrying iodine in the electrolyte. The bleaching was clearly fastest in the cells that contained unpurified electrolyte solvent but the mechanism was present in all the cells. Additionally, the exposure to even relatively small amounts of ultraviolet light seemed to affect detrimentally cell lifetime through accelerated bleaching.Työn kahtena päätavoitteena oli selvittää, vaikuttaako väriaineaurinkokennon elektrolyytin materiaalien puhdistaminen myönteisesti väriaineaurinkokennon suorituskykyyn tai elinikään. Työssä ei tarkasteltu ainoastaan kaikkien elektrolyyttimateriaalien yhtäaikaisen puhdistamisen vaikutusta aurinkokennoihin, vaan eriteltiin myös yksittäisten elektrolyyttikomponenttien puhdistamisen vaikutukset. Lisäksi tutkittiin kennon ikääntymistä aiheuttavia tekijöitä. Tutkimuksessa tehdyn ikääntymismittauksen aikana kaikki testikennot ikääntyivät odotettua nopeammin, minkä vuoksi työn kolmanneksi päätavoitteeksi muodostui havaitun nopean ikääntymisen aiheuttajan löytäminen. Lopulta ultraviolettivalon todettiin olevan erittäin todennäköinen syy ilmiölle. Siksi työssä on käsitelty myös ultraviolettivalon vaikutuksia väriaineaurinkokennojen ikääntymiseen. Työn toissijaisena tavoitteena oli määrittää väriaineaurinkokennojen pitkäaikaisiin ikääntymistutkimuksiin soveltuvat menettelytavat. Työosuus sisälsi ikääntymistutkimuksiin soveltuvien mittausmenetelmien määrittämisen ja sen arvioimisen, missä määrin tutkimuksen aikana väistämättä jonkin verran vaihteleva valointensiteetti vaikuttaa tutkimustulokseen. Myös sopivia tapoja hyödyntää tilastollisia menetelmiä ikääntymistutkimuksen tulosten arvioimisessa on käsitelty. Työssä havaittiin, että elektrolyytin liuottimen puhdistaminen ei vaikuta tuoreen kennon suorituskykyyn, mutta kasvattaa selvästi kennon elinikää. Muilla elektrolyytin ainesosilla ei havaittu olevan tilastollisesti merkittävää vaikutusta kennon elinikään eikä alkuperäiseen suorituskykyyn. Ikääntymisen havaittiin tapahtuvan elektrolyytin vaalentumisen, eli elektrolyytin varauksenkuljettajana toimivan jodin määrän pienenemisen, kautta. Vaalentuminen oli nopeinta oli puhdistamatonta elektrolyytin liotinta sisältävissä kennoissa, mutta havaittavissa kaikissa testikennoissa. Lisäksi ultraviolettivalon todettiin pieninäkin altistuksina nopeuttavan kennojen ikääntymistä

Nanocellulose aerogel membranes for optimal electrolyte filling in dye solar cells

A new method for depositing electrolyte in dye solar cells (DSCs) is introduced: a nanocellulose hydrogel membrane is screen printed on the counter electrode and further freeze-dried to form a highly porous nanocellulose aerogel, which acts as an absorbing sponge for the liquid electrolyte. When the nanoporous dye-sensitized TiO2 photoelectrode film is pressed against the wetted aerogel, it becomes filled with the electrolyte. The electrolyte flows inside the TiO2 film only about ten micrometers (i.e. the TiO2 film thickness) whereas in the conventional filling method, where the electrolyte is pumped through the cell, it flows about 1000-times longer distance, which is known to cause uneven distribution of the electrolyte components due to a molecular filtering effect. Furthermore, with the new method there is no need for electrolyte filling holes which simplifies significantly the sealing of the cells and eliminates one common pathway for leakage. Photovoltaic analysis showed that addition of the nanocellulose aerogel membrane did not have a statistically significant effect on cell efficiency, diffusion in the electrolyte or charge transfer at the counter electrode. There was, however, a clear difference in the short circuit current density and open circuit voltage between the cells filled with the aerogel method and in the reference cells filled with the conventional method, which appeared to be caused by the differences in the electrolyte filling instead of the nanocellulose itself. Moreover, accelerated aging tests at 1 Sun 40 °C for 1000 h showed that the nanocellulose cells were as stable as the conventional DSCs. The nanocellulose aerogel membranes thus appear inert with respect to both performance and stability of the cells, which is an important criterion for any electrolyte solidifying filler material.Peer reviewe

Vision-driven Autocharacterization of Perovskite Semiconductors

In materials research, the task of characterizing hundreds of different materials traditionally requires equally many human hours spent measuring samples one by one. We demonstrate that with the integration of computer vision into this material research workflow, many of these tasks can be automated, significantly accelerating the throughput of the workflow for scientists. We present a framework that uses vision to address specific pain points in the characterization of perovskite semiconductors, a group of materials with the potential to form new types of solar cells. With this approach, we automate the measurement and computation of chemical and optoelectronic properties of perovskites. Our framework proposes the following four key contributions: (i) a computer vision tool for scalable segmentation to arbitrarily many material samples, (ii) a tool to extract the chemical composition of all material samples, (iii) an algorithm capable of automatically computing band gap across arbitrarily many unique samples using vision-segmented hyperspectral reflectance data, and (iv) automating the stability measurement of multi-hour perovskite degradation experiments with vision for spatially non-uniform samples. We demonstrate the key contributions of the proposed framework on eighty samples of unique composition from the formamidinium-methylammonium lead tri-iodide perovskite system and validate the accuracy of each method using human evaluation and X-ray diffraction.Comment: Manuscript 8 pages; Supplemental 7 page

Predictive Modeling of Dye Solar Cell Degradation

Degradation of dye solar cell performance based on the early changes in electrolyte color is predicted, allowing to estimate the lifetime of the dye solar cells even before their efficiency declines. Previous predictive models commonly rely on regression analysis of the predicted parameter; thus, they are unable to capture degradation before a significant decrease in performance. Degradation tests, even when accelerated, may take thousands of hours. As such, recognizing degradation trends early can lead to rewarding cuts in the duration of solar cell development pipelines. With accurate lifetime predictions, researchers can steer materials research to reach longer lifetimes in shorter cycles. The predictive power of our model relies on color changes in the electrolyte that directly correlate with the concentration of tri-iodide charge carriers within it, the loss of which is the predominant degradation mechanism for most liquid-electrolyte dye solar cells. By linking the physical mechanisms inside the cell, which eventually start to degrade the performance of dye solar cells, an early prediction of the lifetime can be made even when the device performance still appears stable. It is exemplified with dye solar cells that integrating architecture-specific knowledge on degradation mechanisms has potential to improve lifetime predictions for photovoltaics.</p

Do Counter Electrodes on Metal Substrates Work with Cobalt Complex Based Electrolyte in Dye Sensitized Solar Cells?

Yes. Testing 7 different metals as a substrate for a counter electrode in dye sensitized solar cells (DSSC) showed that some metals can be a good option for use with cobalt electrolyte. It was found that Stainless steels 304 and 321 as well as Ni and Ti suit well to the counter electrodes in DSSCs with cobalt electrolyte. In these 4 cases both the efficiency and the lifetime were similar to the reference cells on conducting glass substrates. In contrast, the cells with Al, Cu and Zn substrates suffered from both a low efficiency and a poor stability. These three metals had clear marks of corrosion such as apparent corrosion products in the aged cells. Additionally, we also investigated how the different types of catalyst materials perform in the case of a metal counter electrode (stainless steel 304) with cobalt electrolyte in comparison to reference glass cells. Among the 5 different catalyst layers the best results for stainless steel electrode were achieved with low temperature platinization whereas polymer catalysts poly(3,4-ethylenedioxythiophene)-p-toluenesulfone and poly(3,4-ethylenedioxythiophene)-polystyrenesulfone that worked well on the glass worked very poorly on the metal.Peer reviewe

Väriaine- ja perovskiittiaurinkokennojen elinaikatutkimuksia

Dye solar cells (DSCs) and perovskite solar cells (PSCs) are promising future photovoltaics technologies. They demonstrate promise in terms of lower costs and mass-production and could thus help transform photovoltaics into a mainstream energy option. Many applications of photovoltaics, such as building integration, require a lifetime of decades to be economically sensible. This work focuses on understanding the aging mechanisms and extending the lifetime of DSCs and PSCs. In DSCs, the insufficient stability of the electrolyte component is a major weakness. Commonly applied liquid electrolytes are difficult to seal reliably into the cell. Thus, a method for sealing large-area cells utilizing nanocellulose aerogel membranes was developed in this work. The main stability challenge is the diminution of charge carriers in electrolyte (i.e., electrolyte bleaching) when the cells are exposed to environmental stress factors. In this work, purification of electrolyte solvent was observed to halve the progress of bleaching when the cells were exposed to ultraviolet light (UV). Also the application of a UV filter and the change of the redox couple from iodine to cobalt complex effectively suppressed the bleaching. Cobalt complex electrolytes have been regarded as unstable but here it was detected for the first time that the cobalt complex bleaches at a slower rate in comparison to the traditional iodine electrolyte. A perovskite precursor ink was developed in this work for printing carbon based PSCs. In this respect, all the material layers of the cell were manufactured accurately using upscalable methods. Perovskite decomposition under humidity or UV is a major aging mechanism. Here, the exceptionally stable PSCs prepared here were shown to withstand these stress factors in accelerated aging tests for one thousand hours. Also a photographing method was applied to explore perovskite decomposition. A survey of the state-of-the-art degradation studies of PSCs and DSCs revealed insufficient reporting and experimental procedures. Therefore, improved procedures were elaborated upon in this work, which also could contribute to improving the lifetime of DSSC and PSC solar cells.Väriaine- ja perovskiittiaurinkokennot ovat lupaavia tulevaisuuden aurinkosähköteknologioita. Niiden avulla aurinkosähköstä voi tulla energiantuotannon valtavirtaa, kun kennot ovat nykyistä edullisempia ja helpommin teollisessa mittakaavassa valmistettavia. Monissa sovelluksissa, kuten rakennusintegraatiossa, kennoilta vaaditaan jopa vuosikymmenien elinikää, jotta investointi olisi taloudellisesti kannattava. Tässä työssä syvennytään väriaine- ja perovskiittiaurinkokennojen ikääntymismekanismien ymmärtämiseen ja eliniän kasvattamiseen. Stabiiliuden kannalta väriainekennojen heikko lenkki on niiden elektrolyytti. Yleisesti käytettyjen nestemäisten elektrolyyttien sulkeminen kennoon luotettavasti on hankalaa, joten työssä kehitettiin tähän tarkoitukseen suurille kennoille soveltuva, nanoselluloosa-aerogeelimatriisia hyödyntävä menetelmä. Stabiiliuden päähaasteena on elektrolyytin varauksenkuljettajien väheneminen (nk. elektrolyytin vaalentuminen) ympäristön rasitteille altistettuna. Tässä työssä havaittiin, että elektrolyytin liuottimen puhdistaminen puolittaa pääasiallisen ikääntymismekanismin eli elektrolyytin vaalentumisen nopeuden ultraviolettivalolle (UV) altistetuissa kennoissa. Myös UV-suodattimen käytön sekä redox-parin vaihtamisen jodista kobolttikompleksiin havaittiin tehokkaasti hidastavan elektrolyytin vaalenemista. Työssä havaittiin ensimmäistä kertaa, että epästabiiliksi mielletty kobolttikompleksielektrolyytti vaalentuu perinteistä jodielektrolyyttiä hitaammin UV-altistuksessa. Perovskiittikennoille kehitettiin työssä perovskiitin esiasteesta muste, joka soveltuu hiilipohjaisten kennojen valmistamiseen tulostamalla. Näin kennojen kaikki materiaalikerrokset voitiin valmistaa tarkasti laajamittaiseen tuotantoon soveltuvilla menetelmillä. Perovskiittikennoissa merkittävä ikääntymismekanismi on perovskiitin hajoaminen kosteus- tai UV-altistuksessa. Valmistettujen poikkeuksellisen stabiilien kennojen osoitettiin kestävän näitä rasitteita tuhannen tunnin kiihdytetyissä ikääntymistesteissä. Samalla tutkittiin perovskiitin hajoamista valokuvausmenetelmää käyttäen. Työssä analysoitiin perovskiitti- ja väriainekennojen ikääntymistestien laatua viimeaikaisen kirjallisuuden perusteella. Analyysi paljasti puutteellisia kokeellisia menettelyitä sekä riittämätöntä raportointia, joten tässä työssä määriteltiin keinoja ikääntymistestien tason parantamiseen. Laadukkaammat ikääntymistestit voivat edesauttaa väriaine- ja perovskiittikennojen stabiiliuden kasvattamista tulevaisuudessa

Extreme sensitivity of dye solar cells to UV-induced degradation

Present practice to avoid harmful effects of UV light on dye solar cells (DSC) is to use a UV filter. However, we show here that a standard 400 nm UV cutoff filter offers inadequate protection from UV-induced degradation. DSCs that were exposed to only visible light by LED lamps maintained 100% of their initial efficiency after 3000 hours of exposure, whereas the efficiency of DSCs subjected to full light spectrum (Xenon arc lamp) with an efficient UV filter dropped down to 10% of their initial performance already after 1500 hours. Optical analysis of the UV filter confirmed that the amount of light transmitted below 400 nm was negligible. These observations indicate that (a) DSCs can be very sensitive to even minor amount of UV and (b) eliminating the effects of UV light on DSC stability cannot easily be avoided by a UV filter on top of the cell. A detailed analysis of the degradation mechanisms revealed that the culprit to loss of performance was accelerated loss of charge carriers in the electrolyte of theDSCs-a typical symptom of UV exposure. These results suggest that commonly used stability tests under LED illumination are insufficient in predicting the lifetime of DSCs in outdoor conditions. Instead, for such purpose, we recommend solar cell stability to be tested with a full light spectrum and with a suitable UV filter.Peer reviewe

Gel electrolytes with polyamidopyridine dendron modified talc for dye-sensitized solar cells

FAPESP - FUNDAÇÃO DE AMPARO À PESQUISA DO ESTADO DE SÃO PAULOCNPQ - CONSELHO NACIONAL DE DESENVOLVIMENTO CIENTÍFICO E TECNOLÓGICOOrganic–inorganic hybrid layered materials are proposed as additives in a quasi-solid gel electrolyte for dye-sensitized solar cells. Talcs could provide a low-cost and environmentally friendly, as well as abundant, option as gelators. Here, talcs were pr9242045420466FAPESP - FUNDAÇÃO DE AMPARO À PESQUISA DO ESTADO DE SÃO PAULOCNPQ - CONSELHO NACIONAL DE DESENVOLVIMENTO CIENTÍFICO E TECNOLÓGICOFAPESP - FUNDAÇÃO DE AMPARO À PESQUISA DO ESTADO DE SÃO PAULOCNPQ - CONSELHO NACIONAL DE DESENVOLVIMENTO CIENTÍFICO E TECNOLÓGICO2013/05911-12014/06942-0200082/2015-9490241/2012-