Thermal Evaporation–Deposited Hexagonal CDS Buffer Layer to Boost Performance of Sb2(S,Se)3 Solar Cells

Selenium antimony sulfide (Sb2(S,Se)3) is an attractive photovoltaic absorber material owing to its suitable band gap, large absorption coefficient, and photoelectric properties. Chemical bath–deposited cadmium sulfide (CBD-CdS) is the most widely used buffer layer material for Sb2(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 prepared using the thermal evaporation method were used as the buffer layers of Sb2(S,Se)3 photovoltaic devices. Compared with CBD-CdS, thermal evaporation–deposited CdS (TED-CdS) films have a larger band gap and fewer surface defects. The Sb2(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 0.85 eV (CBD-CdS) to 0.76 eV (TED-CdS). Therefore, suppressed electron trap density and charge recombination, as well as improved light harvesting, are achieved. The best efficiency of the device increases from 6.14% to 7.16%