Intrinsic Defect Limit to the Electrical Conductivity and a Two‐Step p‐Type Doping Strategy for Overcoming the Efficiency Bottleneck of Sb 2 S 3 ‐Based Solar Cells

The photovoltaic efficiency increase in Sb 2 S 3 ‐based solar cells has stagnated for 5 years since the highest efficiency of 7.5% was achieved in 2014. One important bottleneck is the high electrical resistivity of Sb 2 S 3 . The first‐principle calculations reveal that the high‐resistivity results from the compensation between the intrinsic donor V S and acceptors V Sb , Sb S , and S Sb which have comparably high concentration (low formation energy). The compensation also limits the improvement of conductivity through direct extrinsic doping. Further calculations of O dopants show that O S has low formation energy, so the dominant intrinsic donor V S can be passivated by O and thus the p‐type doping limit imposed by V S can be overcome. Meanwhile, other p‐type limiting and recombination‐center donor defects can be suppressed under the S‐rich condition, which explains why the highest efficiency is achieved in O‐doped Sb 2 S 3 after sulfurization. Given the unexpected beneficial effects of O doping and sulfurization, a two‐step doping strategy is proposed for overcoming the efficiency bottleneck: 1) use O to passivate the V S and S‐rich condition to suppress other detrimental defects, making p‐type doping feasible and minority carrier lifetime long; 2) introduce other p‐type dopants to increase hole carrier concentration.