New Insight into Sulfurized and Selenized Kesterite–Titania Nanostructures for CdS-free and HTM-free Photovoltaic and Voltage-Modulated Photodetecting Applications

Cu2ZnSnS4 or kesterite and its selenium alloyed counterparts are considered promising for next generation photovoltaic applications due to their excellent optoelectronic properties and earth-abundant, nontoxic composition. In order to alleviate the adverse effects of defects and interfaces on charge separation and transport in current thin film kesterite photovoltaics, new solutions such as the application of an inverted superstrate configuration have been proposed. In this article, sulfurized and selenized kesterite were deposited by solution processing on thin ALD Al2O3 coated TiO2 nanorods to fabricate novel nanostructured devices free of additional buffer layers and hole transfer materials (HTM). The selenized kesterite (CZTSSe) solar cell demonstrated an energy conversion efficiency of 1.85% with high Jsc of ∼20 mA/cm2 while the sulfurized kesterite (CZTS) device showed lower solar cell efficiency but excellent photodetecting properties under reverse bias with adjustable working window from visible-only to UV–vis–NIR range.