Investigation on Carrier Dynamics and Photovoltaic Performance of Bifacial Cztse

Though there is a gap of about 10% in conversion efficiency, Cu2ZnSn(S,Se)4 (CZTSSe) has been considered to be the most promising material to replace Cu(In,Ga)Se2 for application in photovoltaics. One of the issue addressed to Cu(In,Ga)Se2 is the shortage of indium owing to competition between the display industry. To overcome this issue, CZTSSe was developed as a promising substituted material due to its earth-abundant composition. The efficiencies of CZTSSe-based solar cells have remained much lower than the theoretical limit, mainly due to limited open-circuit voltages (Voc). The phenomenon is not well understood and has been attributed to intrinsic point defects in the CZTSSe layer that cause severe band tailing. There are also both theoretical and experimental indications that the pure selenide CZTSe phase possesses shallower defect levels compared with the pure sulfide CZTS phase. To clarify the mechanisms underlying, we will have systematic efforts by studying the compositional simpler quaternary CZTSe system, rather than the more complex CZTSSe system. In order to rule out the The main objective of this project is to achieve the low-toxicity and high-efficiency photovoltaic devices. Research categories include both fundamental physics and practical implementation. Improving CZTS device performance will require better understanding of the link between material properties and processing conditions, and their influence on junction characteristics, carrier collection, and recombination mechanisms. Carrier dynamics will be examined using TRPL, CAFM, SCM, Raman spectra and discussed in detail. First, we use the thermal evaporation, sputtering and non-toxic selenization systems to prepare high quality CZTSe absorber layer. The aim of this stage is to develop pure CZTSe thin films without secondary phases and realized the rectification characteristic. The correlation between carrier dynamics and process conditions will be examined. Secondly, a non-uniform layer of nanocrystal quantum dots aggregates is deposited between the transparent conductive oxide and a CdS/CZTS p-n junction using low cost pulsed-spray deposition. This work is important in developing non-toxic, earth-abundant elements thin-film solar cell. Finally, we propose a device structure containing the combination of ZnO nanostructures and CZTSe for superstrate and future bifacial applications. The bifacial device structure allows the sunlight incident from both front and rear contact, meriting the increased conversion efficiency. Moreover, the bifacial device can be also potentially applied into the tandem devices, solar windows, solar house roof, etc. due to the transparent back contact allowing the sunlight pass through the entire solar cell. The achievements of this project can make substantial progress in developing CZTSe solar cells providing environmental and manufacturing benefits.

Project ID:PA10701-0200
External Project ID:MOST105-2112-M182-001-MY3