Controllable orientations for Sb2S3 solar cells by vertical VTD method

Antimony sulfide (Sb2S3) is a promising photoelectric material because of its wide bandgap approximately 1.7 eV for next-generation solar cells, high optical absorption coefficient, and its green and earth-abundant constituents. Different to traditional cubic structure photovoltaic materials, Sb2S3 holds one-dimensional crystal structure and its thin film with [hk1] preferred orientation shows one-order-higher carrier transport mobility. However, all the reported Sb2S3 films exhibited [hk0] preferred orientation on CdS-based superstrate device structure up to now. Thus, it is indispensable to study the controllable-orientations Sb2S3 film deposition and the relationship between the orientation and performances. In this paper, we develop a vertical vapor transport deposition (V-VTD) method, which can tune the preferred orientation of Sb2S3 thin film from [hk0] to [hk1] by reaction recipe monitoring. Combining the experiment results, a reasonable deposition/reevaporation competing model is suggested to explain above orientation conversion mechanism. The device efficiency increases from less than 2% to about 4% with the orientation of Sb2S3 film changing from [hk0] to [hk1]. By fine regulating the technique of deposition, the device with [hk1] orientation has better crystallinity, lower interface recombination, and higher built-in voltage comparing with the [hk0] one. Finally, a champion power conversion efficiency (PCE) of 4.5% has been achieved, and the V-OC of 730 mV is the top value among the Sb2S3 solar cells. The present versatile orientation tuning strategy could overcome the bottleneck of strong anisotropic materials and show high potential for noncubic material deposition and related optoelectronic device performance enhancement.