Li-based selenized Cu2ZnSnS4 surface: Possible route to overcoming voc-deficit of kesterite solar cells

Usually, open-circuit voltage (Voc) of thin film solar cells significantly depends on the band bending at the front interface of an absorber/buffer. The failed band bending at a Cu2ZnSnS4/CdS (CZTS/CdS) interface severely hinders the increase in Voc due to the excessively high concentration of holes at the CZTS side. Alleviating the strong p-type or converting it to weak n-type at the CZTS surface is a credible idea to overcome the Voc− deficit. First-principles calculations show that the Li-based selenized CZTS surface presents the desired property with excellent advantages: (i) The greatly improved defects and band offset suppress carrier nonradiative recombination and facilitate electrons transmission, respectively. (ii) Its intrinsic weak n-type characteristic effectively promotes the large band bending at the interface.