Fabrication of high-efficiency Cu2(Zn,Cd)SnS4 solar cells by a rubidium fluoride assisted co-evaporation/annealing method

Abstract

Recently, kesterite Cu₂ZnSnS₄ (CZTS) has been regarded as a promising candidate for future light absorbers due to its excellent photovoltaic potential. To further improve the efficiency of associated solar cells, both the bulk and interface issues, which give rise to detrimental carrier collection loss, are the key problems that need to be resolved. Herein, by using a thermal co-evaporation/annealing method, we have systematically investigated the Rb incorporation effects on the quality of Cu₂(Cd,Zn)SnS₄ (CCZTS) thin films and related solar devices. The results show that the Rb incorporation could engineer both the bulk and interface significantly, specifically improving bulk quality with enhanced grains and suppressed defects, passivating the rear interface with less secondary phase accumulation, and forming a favorable front band alignment. Benefiting from these multifunctional benefits, carrier collection efficiency is greatly improved with the enhancement of short-circuit current density (J_SC) and open-circuit voltage (V_OC). As a result, a champion efficiency of 10.64% is achieved, which is the highest value for pure sulfide CZTS solar cells made by the thermal evaporation method.