The photovoltaic efficiency increase in Sb2S3‐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 Sb2S3. The first‐principle calculations reveal that the high‐resistivity results from the compensation between the intrinsic donor VS and acceptors VSb, SbS, and SSb 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 OS has low formation energy, so the dominant intrinsic donor VS can be passivated by O and thus the p‐type doping limit imposed by VS 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 Sb2S3 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 VS 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.

The chemical trends in the thermodynamic stability and band gaps of 980 A2B+B3+X6 halide double perovskites are revealed based on high-throughput first-principles calculations. To accurately predict the stability with respect to phase decomposition, all known metal halides in the Materials Project database are considered as the competing compounds. The energies above the convex hull show that only 112 of 980 double perovskites are stable and 27 double perovskites that had been predicted to be stable in the literature are actually unstable after considering more competing compounds. The stability of these double perovskites is determined mainly by A, X, and B+ elements and increases gradually as A becomes heavier (from Li to Cs) and X becomes lighter (from I to F). The band gaps are determined mainly by X, B+, and B3+ elements, decreasing monotonically as X becomes heavier while changing nonmonotonically as B+ and B3+ change. These chemical trends provide clear instructions for the design of double perovskites with good stability and suitable band gaps for various applications, i.e., through choosing heavier A cations (e.g., large organic cations), stable double perovskites can be designed with band gaps tunable in a wide range of 0–7 eV (infrared to ultraviolet); however, through choosing light X anions, stable double perovskites can be designed with only wide band gaps.

It was believed that the Se‐rich synthesis condition can suppress the formation of deep‐level donor defect VSe (selenium vacancy) in Sb2Se3 and is thus critical for fabricating high‐efficiency Sb2Se3 solar cells. However, here it is shown that by first‐principles calculations the density of VSe increases unexpectedly to 1016 cm−3 when the Se chemical potential increases, so Se‐rich condition promotes rather than suppresses the formation of VSe. Therefore, high density of VSe is thermodynamically inevitable, no matter under Se‐poor or Se‐rich conditions. This abnormal behavior can be explained by a physical concept “defect‐correlation”, i.e., when donor and acceptor defects compensate each other, all defects become correlated with each other due to the formation energy dependence on Fermi level which is determined by densities of all ionized defects. In quasi‐1D Sb2Se3, there are many defects and the complicated defect‐correlation can give rise to abnormal behaviors, e.g., lowering Fermi level and thus decreasing the formation energy of ionized donor VSe2+ in Se‐rich Sb2Se3. Such behavior exists also in Sb2S3. It explains the recent experiments that the extremely Se‐rich condition causes the efficiency drop of Sb2Se3 solar cells, and demonstrates that the common chemical intuition and defect engineering strategies may be invalid in compensated semiconductors.

Molecule damage under TEM electron beam illumination is studied using a systematical ab initio method. Three main dissociation paths are revealed which explains the experimentally observed mass spectra of the dissociation fragments of the C2H6O2+.