Chemical Bath Solution In-Addition Enabled Grain Boundary and Heterojunction Interface Defects Mitigation Achieving 12.1% Efficiency CZTS Solar Cell

The performance of wide bandgap Cu 2 ZnSnS 4 (CZTS) thin film solar cells is limited by serious recombination due to high concentration of defects and “cliff-like” conduction band offset (CBO) at the heterojunction. The state-of-the-art strategies tackling these issues are post heat treatment and alternative buffer layer. Here, we address these issues by adding InCl 3 to the chemical bath deposition solution (CBD-In-addition) for CdS buffer layer. At early CBD stage, In 3+ sufficiently substitute Zn 2+ near CZTS absorber surface and along the grain boundaries (GBs), enabled by smaller size than Cd 2+ and no complexation with NH 3 , resulting in highly conductive GBs with beneficial upward band bending. Further, the incorporation of In 3+ into CdS ((Cd,In)S) improved buffer layer n-type conductivity, alleviated heterojunction lattice mismatch and enlarged buffer layer bandgap, resulting in a coherent CZTS/(Cd,In)S interface, a “spike-like” CBO, and a more transparent buffer layer. These effects lead to 12.14% efficiency CZTS solar cell, improved by 31% compared to reference device (9.29%). This is the highest efficiency sulfide CZTS solar cell with chemical bath deposited buffer layer without post heat-treatment. The simple and synergetic defects mitigation strategy is expected to advance other wide bandgap chalcogenide thin film solar cells.