Carregant...
Tipus de document
TesiVersió
Versió publicadaData de publicació
Si us plau utilitzeu sempre aquest identificador per citar o enllaçar aquest document: https://hdl.handle.net/2445/107092
Development of Cu2ZnSnSe4 Based Thin Film Solar Cells by PVD and Chemical Based Processes
Títol de la revista
Autors
Director/Tutor
ISSN de la revista
Títol del volum
Resum
[eng] Nowadays mono- and multicrystalline silicon have the highest market share of all PV technologies but thin film solar cells based on CdTe or Cu(In,Ga)Se2 (CIGS) absorbers recently show promising high power conversion efficiency values and due to their short energy payback time, minimal use of high purity material and low cost, they attract more and more attention. However, one concern of thin film PV based on CdTe or CIGS is the use of scare elements like tellurium or indium and gallium which could become a bottleneck if the technology wants to scale up to the terawatt level. Therefore, there is a high interest to replace these scare elements by more abundant ones and find suitable earth abundant photovoltaic absorbers. Cu2ZnSnSe4 (CZTSe) or Cu2ZnSnS4 (CZTS) and its sulphur-selenide solid solution are promising candidates to replace CIGS as absorber material due to its composition of more earth abundant elements. In literature CZTSe and CZTS are referred to as kesterite due to its crystal structure. However, there is still a large gap between power conversion efficiencies of solar cells based on kesterite absorber material and more established thin film solar cells, thus intensive research is still necessary to close this gap. The main goal of this thesis was to develop and optimize heterostructure solar cells based on Cu2ZnSnSe4 absorbers, by cost effective physical vapour deposition (PVD) and chemical based processes. Special focus is put on an improved understanding of the influence of the surface properties of kesterite absorbers on device performance and furthermore to optimize the front interface, i.e. buffer layer as well as the kesterite absorber layer itself. A detailed study investigating the influence of the surface chemistry on device performance is presented. After a chemical etching to remove unwanted ZnSe secondary phases formed during CZTSe absorber synthesis a low temperature post deposition annealing at 200ºC of the full solar cell is necessary to improve device efficiencies from below 3% to over 8%. X-ray photoelectron spectroscopy (XPS) surface analysis showed that this post deposition annealing promotes the diffusion of Zn towards the surface and Cu towards the bulk resulting in a Zn enriched and Cu depleted surface region, which is crucial for high device performance. Additionally experimental surface treatments confirm the necessity of a Cu-poor and Zn-rich surface and the reason for this beneficial surface composition are discussed in detail. Furthermore, the CdS buffer layer which is typically used in kesterite based heterostructures solar cells was optimized and allowed improvements in device performance of 1% absolute. This optimization was further extended to Cd-free ZnS(O,OH) buffer layer. Efficiencies close to that of CdS reference solar cells could be achieved using optimized ZnS(O,OH) buffer layer. Additionally to the front interface optimization, a Ge assisted crystallization process for nanocrystalline CZTSe precursors was developed which largely increase grain growth and boost open circuit voltages (Voc) to promising high values due to the elimination of deep defects. Since the low Voc values is identified of one of the main bottlenecks of kesterite technology, the improvements achieved are highly promising and give important insight for further possible optimizations.
Descripció
Matèries (anglès)
Citació
Col·leccions
Citació
NEUSCHITZER, Markus. Development of Cu2ZnSnSe4 Based Thin Film Solar Cells by PVD and Chemical Based Processes. [consulta: 9 de desembre de 2025]. [Disponible a: https://hdl.handle.net/2445/107092]