DFT Investigation of Structural Stability, Optical Properties, and PCE for All-Inorganic Cs_x (Pb/Sn)_y X_z Halide Perovskites

Employing all-inorganic perovskites as light harvesters has recently drawn increasing attention owing to the strong-bonded inorganic components in the crystal. To achieve the systematic and comprehensive understanding for the structures and properties of Cs-x(Pb/Sn)(y)X-z (X = F, Cl, Br, I) perovskites, this work provides the comparison details about crystal structures, optical properties, electronic structures and power conversion efficiency (PCE) of 18 perovskites. The suitable band gaps are detected in CsSnCl3-Pm3m (0.96 eV), gamma-CsPbI3-Pnma (1.75 eV), and CsPbBr3-Pm3m (1.78 eV), facilitating the conversion from absorbing photon energy to generating hole-electron pairs. gamma-CsPbI3-Pnma and CsSnI3-P4/mbm show superior visible-absorption performance depending on their higher absorption coefficient (alpha); meanwhile, strong peaks can be observed in the real part (Re) of photoconductivity of CsPbBr3-Pbnm, gamma-CsPbI3-Pnma, and CsSnI3-P4/mbm in the visible-light range, implying their better photoelectric conversion abilities. The perovskite/tungsten disulfide (WS2) heterojunctions are constructed to calculate the PCE. Although just the PCE result (14.43%) of CsSnI3-Pnma/WS2 is reluctantly competitive, the predictions of PCEs indicate that the PCE of PSCs (perovskite solar cells) can be improved by not only regulating the perovskite to upgrade its own performance but also designing the PSC structure reasonably including the selection of appropriate ETL/HTL (electron/hole transport layer), etc.