Extrinsic dopants in quasi-one-dimensional photovoltaic semiconductor Sb2S3: A first-principles study

Extrinsic elements such as C, Zn, Sn, Bi, and Ti had been doped into Sb2S3 in order to increase the electrical conductivity and thus the photovoltaic efficiency. However, the influences of these dopants are so far unclear. Using the first-principles calculations, we show that (i) Zn and Sn doping can slightly increase the p-type conductivity of Sb2S3 through forming ZnSb2 and SnSb2 acceptors, explaining the observed increase in photocurrent and carrier concentration; (ii) in contrast, the formation energies of C dopants on different sites are high, which means C doping cannot increase the conductivity of Sb2S3 obviously, so the highly reduced resistivity of C-doped Sb2S3 in experiments cannot be explained and the effects of C doping should be revisited; (iii) Bii acts as the carrier recombination center, so the photocurrent of the Bi-doped Sb2S3 solar cells decreases; and (iv) the formation energies (concentration) of Tii and TiSb1 donors are extremely low (high), so the photocurrent of the Ti doped Sb2S3 solar cells increases significantly. Considering the influences on both electrical conductivity and carrier non-radiative recombination, we propose that Pb and Cl are relatively benign p-type and n-type dopants, respectively. Cl doping can make Sb2S3 show high n-type conductivity and long minority carrier lifetime, thus offering a promising method for overcoming the current efficiency bottleneck of Sb2S3 solar cells.