Minority lifetime and efficiency improvement for CZTS solar cells via Cd ion soaking and post treatment

Short minority carrier lifetime and low open circuit voltage (Voc) are key issues limiting the current efficiency development for Cu2ZnSnS4 (CZTS) thin film solar cells. This work presents the use of Cd ion soaking and post-heat treatment to increase the lifetime and Voc of CZTS. The time-resolved photoluminescence (TRPL) results confirmed that Cd ion soaking and post heat treatment is effective in enhancing the minority lifetime, from ∼10 ns up to ∼28 ns. With analyses of the current density- voltage (J-V) curves and external quantum efficiency (EQE) data, Cd ion soaking and subsequent post heat treatment is found to greatly reduce the recombination and improve the junction quality, contributing to a ∼70 mV Voc enhancement and resulting in the increased device efficiency of 7.6%, from 5.9%. •Cd ion soaking with related post annealing effectively boost efficiency of CZTS solar cell.•PL technologies reveal the significant enhanced minority lifetime.•7.6% power conversion efficiency has been achieved for sol-gel CZTS solar cell.