Hybrid solar cells

Solarzellen sind als "alternative Energiequelle" mehr denn je im Fokus von Forschung und Entwicklung. Derzeit basieren praktisch alle kommerziell erhältlichen Module auf klassischen Halbleitermaterialien wie Silizium. Dieses ist in sehr hoher Reinheit und einkristallin verfügbar, woraus sehr gute Materialeigenschaften resultieren. Gewinnung und Reinigung sind allerdings sehr kostenintensiv und energieaufwendig. Insbesondere weist Silizium, im Vergleich zu Farbstoffmolekülen, einen sehr geringen Absorptionskoeffizienten auf. Durch Verwendung von organischen Halbleitern kann daher u.a. die Schichtdicke von Solarzellen drastisch reduziert werden. Neben d\"unnen Schichten verspricht man sich von günstiger Prozessierung erheblich niedrigere Herstellungskosten. Aufgrund anderer Transportmechanismen (Hopping-Transport) zeigen organische Halbleiter eine erheblich niedrigere Ladungsträgermobilität als anorganische Halbleiter (Bandtransport). Zudem ist in organischen Solarzellen nach der Photonenabsorption eine Trennung der noch gebundenen Ladungträger (Exzitonen) nötig. Die Kombination aus organischen und anorganischen Halbleitern für die Photovoltaik wird Hybrid-Solarzellen genannt. Hiervon verspricht man sich die Nutzung der hohen Absorbanz des organischen Materials und der guten Transporteigenschaften der verwendeten anorganischen Halbleiter. Bislang kamen hauptsächlich Polymere zum Einsatz. Wenig Erfahrung gibt es hingegen in der Kombination von anorganischen Halbleitern und kleinen Molekülen mit aromatischen Ringen. Diese zeigen gute optische Eigenschaften. Dies wurde in der vorliegenden Arbeit am Beispiel von Zink(II)-Phthalocyanin (ZnPc) nachgewiesen. Optische Spektroskopie wurde verwendet, um die optischen Konstanten, Schichtdicke und Rauigkeit der Schichten simultan zu bestimmen. Eine organisch-anorganische Grenzfläche innerhalb einer Hybrid-Solarzelle wurde aus ZnPc und Zinkoxid hergestellt und charakterisiert. Hierfür wurde mittels Photelektronenspektroskopie der Verlauf der Bandstruktur innerhalb des Bauelemtes nachvollzogen. Mit Hilfe dieser Methode wurden Abschätzungen für die Leerlaufspannung getroffen und anhand von Strom-Spannungs-Kennlinien überprüft. Die Kennlinien weisen einen sehr geringen Photostrom auf. Die Ursache dafür scheint eine schlechte Exzitonendissoziation zu sein. Hierfür wurden zwei Verbesserungsansätze gewählt. Zum einen wurde die Bandstruktur mittels Dotierung modifiziert, um die Energie zu erhöhen, welche für die Exzitonentrennung zur Verfügung steht. Zum anderen sollte durch Nanodrähte die Distanz zum dissoziationsverursachenden p-n-Übergang verringert werden, um so in die Reichweite der Exzitonen zu gelangen. Anhand von spektral aufgelösten Photostrommessungen konnte die Exzitonendiffusionslänge auf 16 nm bestimmt werden. Eine Steigerung der Effizienz wurde leider nicht erzielt

In situ syntheses of semiconducting nanoparticles in conjugated polymer matrices and their application in photovoltaics

Hybrid solar cells based on conjugated polymers and inorganic semiconducting nanoparticles combine beneficial properties of organic and inorganic semiconductors and are, therefore, an exciting alternative to pure organic or inorganic solar cell technologies. Several approaches for the fabrication of hybrid solar cells are already elaborated and explored. In the last years routes have emerged, where the nanoparticles are prepared directly in the matrix of the conjugated polymer. Here, the conjugated polymer prevents the nanoparticles from excessive growth and thereby makes additional capping agents obsolete. This review focuses on in situ preparation methods of inorganic semiconducting nanoparticles in conjugated polymers in view of applications in hybrid solar cells. The details, advantages and disadvantages of the different in situ methods are critically examined and put in comparison to the classical route where pre-synthesized nanoparticles are used. Various key factors influencing the solar cell performance as well as future strategies for increasing the overall efficiency of hybrid solar cells prepared via in situ routes are discussed

A Theoretical Study on the Operation Principle of Hybrid Solar Cells

In this work, the operation mechanism of hybrid solar cells is studied explicitly. The excitation, diffusion and dissociation of singlet and triplet excitons and charge transport of free charge carriers are studied and their corresponding rates are calculated for a flexible P3HT:SiNW hybrid solar cell. The rates are found to be faster for singlet than triplet excitons. Possible loss mechanisms in hybrid solar cells have also been highlighted

Solution Processable Hybrid Solar Cells Based on Semiconductor Nanoparticles

abstract: The goal of this work is to develop low cost and highly efficient hybrid solar cells based on semiconductor nanoparticles (NPs). Hybrid solar cells have been demonstrated to take advantages of both inorganic and organic semiconductors by employing simple soluble process. In order to improve the power conversion efficiency (PCE), the bulk heterojunction (BHJ) of cadmium selenide (CdSe) tetrapods (TPs) and poly (3-hexylthiophene) (P3HT) are introduced as an electron acceptor and donor, respectively. The dimension of CdSe TPs and the 3D spatial distribution of CdSe TPs:P3HT photoactive blends are investigated to improve optical and electrical properties of photovoltaic devices. Hybrid solar cells having long-armed CdSe TPs and P3HT establish higher PCE of 1.12% when compared to device employing short-armed TPs of 0.80%. The device performance are improved by using longer armed CdSe TPs, which aids in better percolation connectivity and reduced charge hopping events, thus leading to better charge transport. The device architecture of hybrid solar cells is examined to assist vertical phase separation (VPS). Improvement of VPS in hybrid solar cells using CdSe TPs:P3HT photoactive blends is systematically manipulated by solution processed interfacial layers, resulting in enhanced device performance. Multi-layered hybrid solar cells assist better light absorption, efficient charge carrier transport, and increase of the surface contact area. In this work, hole transport assisting layer (HTAL)/BHJ photoactive layer (BPL)/electron transport assisting layer (ETAL) or HTAL/BPL/ETAL (HBE) multi-layered structure is introduced, similarly to p-type layer/intermixed photoactive layer/n-type layer (p-i-n) structure of organic photovoltaic devices. To further control the improvement of the device performance, the effects of nano-scale morphology from solvents having different boiling points, the various shapes of semiconductor NPs, and the emergence of blending NPs are demonstrated. The formation of favorable 3D networks in photoactive layer is attributed to enhance the efficient charge transport by the optimized combination of semiconductor NPs in polymer matrix.Dissertation/ThesisPh.D. Materials Science and Engineering 201

Molecular-Level Switching of Polymer/Nanocrystal Non-Covalent Interactions and Application in Hybrid Solar Cells

Hy brid composites obtained upon blending conjugated polymers and colloidal inorganic semiconductor nanocrystals are regarded as attractive photo-active materials for optoelectronic applications. Here we demonstrate that tailoring nanocrystal surface chemistry permits to exert control on non-covalent bonding and electronic interactions between organic and inorganic components. The pendant moieties of organic ligands at the nanocrystal surface do not merely confer colloidal stability while hindering charge separation and transport, but drastically impact morphology of hybrid composites during formation from blend solutions. The relevance of our approach to photovoltaic applications is demonstrated for composites based on poly(3-hexylthiophene) and Pbs nanocrystals, considered as inadequate before the submission of this manuscript, which enable the fabrication of hybrid solar cells displaying a power conversion efficiency that reaches 3 %. Upon (quasi)steady-state and time-resolved analisys of the photo-induced processes in the nanocomposites and their organic and inorganic components, we ascertained that electron transfer occurs at the hybrid interface yielding long-lived separated charge carriers, whereas interfacial hole transfer appears slow. Here we provide a reliable alternative aiming at gaining control over macroscopic optoelectronic properties of polymer/nanocrystal composites by acting at the molecular-level via ligands' pendant moieties, thus opening new possibilities towards efficient solution-processed hybrid solar cells

Carbon Nanotubes - Si Hybrid Solar Cells

This short review describes recent results in the field of carbon nanotube (CNT) – Si hybrid photovolta-ics (PV) focusing on advantages of semiconducting carbon nanotubes over other organic materials used in organic- Si composite photosensing materials. Possible mechanisms of charge phogeneration at CNT- Si in-terface and chargte transport are discussed. Perspectives and future trends in research of this novel class of PV nanohybrids are presented as well. When you are citing the document, use the following link http://essuir.sumdu.edu.ua/handle/123456789/3549

Hybrid solar cells from water-soluble polymers

We report on the use of a water-soluble, light-absorbing polythiophene polymer to fabricate novel photovoltaic devices. The polymer is a water-soluble thiophene known as sodium poly[2-(3-thienyl)-ethoxy-4-butylsulfonate] or PTEBS. The intention is to take advantage of the properties of conjugated polymers (flexible, tunable, and easy to process) and incorporate the additional benefits of water solubility (easily controlled evaporation rates and environmentally friendly). The PTEBS polythiophene has shown significant photovoltaic response and has been found to be effective for making solar cells. To date, solar cells in three different configurations have been produced: titanium dioxide (TiO2) bilayer cells, TiO2 bulk heterojunction solar cells, and carbon nanotubes (CNTs) in bulk heterojunctions. The best performance thus far has been achieved with TiO2 bilayer devices. These devices have an open circuit voltage (Voc) of 0.84V, a short circuit current (Jsc) of 0.15 mA/cm2, a fill factor (ff) of 0.91, and an efficiency (η) of 0.15 %