Na incorporation controlled single phase kesterite Cu₂ZnSnS₄ solar cell material

It is theoretically and experimentally challenging to fabricate single phase Cu₂ZnSnS₄ (CZTS) and more difficult to synthesize it by sol–gel method. Theoretical work reveals that Na can passivate the dangling bonds in the grain boundaries of CZTS and thus enhance the photovoltaic performance. Therefore, Na incorporation may be an effective way in passivating defects in CZTS films and fabricating CZTS with high quality and single phase. In this study, we will try to incorporate Na into CZTS films by sol–gel method to help passivate defects in CZTS and achieve single phase kesterite CZTS films using a different solvent 2-methoxybutanol. Different Na/(Cu + Zn + Sn) atomic ratios (0%-3%) will be employed. Through controlling Na incorporation amount in solution, we can prevent the generation of other phases like SnO₂ and a pure single phase kesterite CZTS can be achieved. The optical band gap of the optimal CZTS film is 1.24 eV. All Na doped CZTS films show p-type conduction behavior.