Achieving beyond 26.6% efficiency for graded bandgap perovskite solar cell: Theoretical study

The graded energy band gap is an effective method for improving solar spectrum efficiency. To reduce the short-circuit current density (JSC) losses, creation of suitable spike-like alignment at the electron transport (ETL)/perovskite junction is a proper method. Also, simulations model is calibrated with the experimental current-voltage (J–V) and power conversion efficiency (PCE) to validate obtained data. The graded FAPbI3 perovskite solar cell has been proposed, and the effect of (Br, I) on the device efficiency is researched. The results illustrate that iodide values in FAPb (IxBr1-x)3 significantly influence the adjustment of conduction band energy states at the perovskite/ETL interface. The Br flexibility ranging from 0% to 40% allows the target perovskite solar cell (PSC) to produce an optimum conduction band offset (CBO) at the perovskite/ETL interface. The CBO creation between the FAPbI3/ETL causes achieving (open-circuit voltage) VOC to 1.22 V, JSC to 26.9 mA cm−2, and fill factor (FF) to 81.1. Here, we demonstrate that graded energy band gap PSC could achieve steady-state conversion efficiencies of ∼26.63%. According to the results, this enhancement is owing to the proper carrier's transport among the perovskite/ETL junction due to a recombination decrement in the junction with spike-like band alignment.