The design of SnO ₂ ‐dominated electron transport layer for high efficiency Sb ₂ (S,Se) ₃ solar cells

Antimony chalcogenide semiconductors have received much attention for serving as promising light harvesters owing to their excellent materials and photoelectric properties. Particularly, Sb 2 (S,Se) 3 alloyed materials share the complementary advantages of Sb 2 S 3 and Sb 2 Se 3 , showing a tunable bandgap ranging from 1.1 to 1.7 eV. In Sb 2 (S,Se) 3 solar cells, although Sb 2 (S,Se) 3 absorber material shows a friendly character to the environment, the widely used CdS electron transport layer (ETL) that often affords considerable device efficiencies is not environmental friendly; moreover, CdS often suffers from severe parasitic light absorption due to its relatively narrow band gap of 2.4 eV. Hence, the exploration of Cd‐free or less‐Cd‐based ETLs is urgently needed. Herein, SnO 2 ‐dominated ETLs are carefully designed by optimizing the concentration of SnO 2 precursor solutions and spin‐coating cycles, and are further constructed over 8%‐efficient Sb 2 (S,Se) 3 solar cells, together with the effective modification of SnO 2 /Sb 2 (S,Se) 3 with an ultrathin CdS layer. The morphological and optical–electrical properties of ETLs, the performance of solar cells, and the related charge recombination mechanisms are discussed. The designed SnO 2 ‐dominated ETLs have sharply decreased the use of heavy metal Cd, thereby reducing the risk of environmental pollution. This work provides important enlightenment for designing totally environmentally friendly Sb 2 (S,Se) 3 solar cells.