Bifacial Cu2ZnSn(S,Se)4 Thin Film Solar Cell Based on Molecular Ink and Rapid Thermal Processing

The use of transparent conducting oxides (TCO) as a back contact for Cu2ZnSn(S,Se)(4) (CZTSSe) thin film solar cell enables light absorption from both front and rear sides and allows for the fabrication of semi-transparent photovoltaic devices. However, the CZTSSe solar cell based on TCO substrate suffers from high parasitic losses owing to the long post-annealing time at elevated temperature required for high-quality absorber. This work aims to overcome this issue by carefully tailoring the annealing conditions to obtain high-performance solar cell. Rapid thermal processing is used to instantaneously generate high Se vapor pressure at target temperature and shorten the annealing time. The crystalline quality, morphology, and particularly the photovoltaic performance of the resulting CZTSSe thin film are systematically investigated. It is found that the increase of annealing temperature and time improves the crystalline quality but unfortunately deteriorates the device performance owing to increasing parasitic losses. Increasing the amount of Se allows to get highly crystalline absorber within 7 min of annealing, yielding a total area 5.56% efficient CZTSSe solar cell with front illumination resulting from reducing parasitic losses. This work provides a simple approach to preserve the back contact without using a complex interfacial layer.

Automated summary

This study aims to achieve high-performance CZTSSe solar cells by carefully tailoring annealing conditions and using rapid thermal processing to shorten the annealing time. It is found that increasing annealing temperature and time can improve crystalline quality but may deteriorate device performance due to increasing parasitic losses. By increasing the amount of Se, a highly crystalline absorber can be obtained within a short annealing time, resulting in a 5.56% efficient CZTSSe solar cell with reduced parasitic losses.