Thermal evaporation–deposited hexagonal CdS buffer layer with improved quality, enlarged band gap, and reduced band gap offset to boost performance of Sb2(S,Se)3 solar cells

Chemical bath–deposited cadmium sulfide (CBD-CdS) is the most widely used buffer layer material for antimony selenosulfide (Sb 2 (S,Se) 3 ) photovoltaic devices , but its medium band gap, large band gap offset with transparent conducting oxides , and surface defects must be addressed to improve its applicability. Hexagonal CdS films (60 nm thick) prepared using the thermal evaporation method were used as the buffer layers of Sb 2 (S,Se) 3 photovoltaic devices. Compared with CBD-CdS (60 nm thick), thermal evaporation–deposited CdS (TED-CdS) films have a larger band gap and fewer surface defects. The Sb 2 (S,Se) 3 film deposited on TED-CdS is more compact, and its 1D ribbons are stacked more vertically to the substrate. The band gap offset between CdS and fluorine-doped tin oxide glass decreases from 0.76 eV (CBD-CdS) to 0.60 eV (TED-CdS). Therefore, suppressed electron trap density and charge recombination, as well as improved light harvesting, are achieved. By replacing CBD-CdS with TED-CdS, the best device efficiency increases from 6.14 % to 7.16 %, with the open circuit voltage, short-circuit current density, and fill factor increasing from 0.660 V, 15.96 mA/cm 2 , and 58.37 % to 0.664 V, 17.39 mA/cm 2 , and 62.85 %, respectively. The device stability and reproducibility are also improved.