Influence of ZnO polymorphs as electron transport layers for Cs2AgBiBr6-based perovskite solar cells

This study investigates ZnO polymorphs as electron transport layers (ETLs) in Cs 2 AgBiBr 6 -based perovskite solar cells (PSCs) through DFT and SCAPS-1D simulations. DFT + U method were used to find the band gaps ( E g ) for ZnO polymorphs, which were 3.31 eV for tetragonal, 3.13 eV for hexagonal, and 3.15 eV for cubic. The cubic phase shows the highest electron mobility of 72 cm 2 V −1 s −1 , and the hexagonal phase has the highest hole mobility at 54 cm 2 V −1 s −1 . Optical analysis reveals the minimal visible-light absorption of selected ZnO polymorphs. Enhanced absorption in the hexagonal phase is attributed to lattice anisotropy, whereas the cubic phase exhibits reduced optical transitions due to its high symmetry. Device simulation shows that the optimum tetragonal phase delivers the highest PCE of 10.99%. Increasing the ETL thickness and raising the cell temperature negatively impact the PCE. Whereas increasing donor density and a wider E g improve the performance of solar cells. Interface defect density is identified as the primary limiting factor, whereas bulk defects have a weaker impact. This study demonstrates the prospects of ZnO polymorphs as efficient, tunable, and low-cost ETLs to boost the performance of Cs 2 AgBiBr 6 -based PSCs.