Optimization of inverted planar perovskite solar cells with environment-friendly MAPb0.25Ge0.75I3 absorber approaching Shockley Queisser limit for efficiency

Abstract

The search for an environmentally benign substitution of toxic lead (Pb) in MAPbI3 –based perovskite solar cells has so far resulted in a compromised performance like poorer efficiency, which is more pronounced in inverted planar (p-i-n) structure. A few theoretical studies have revealed that mixed cation perovskites with low Pb-content, MAGe0.75Pb0.25I3, can have an optical bandgap between 1.33 and 1.41 eV, a bandgap range that can attain maximum efficiency indicated by Shockley Quiesser (SQ) limit. With the motivation of finding an environmental friendly as well as high performing perovskite solar cells, an inverted planar cell configuration is simulated utilizing MAGe0.75Pb0.25I3 as the absorber with commonly used transport layers. The simulation model is optimized based on MAGe0.75Pb0.25I3 material parameters (bandgap, Eg and electron affinity, χ) and film properties (thickness, bulk, and interface defect densities). It is observed that landmark efficiency over 30% is obtainable with Eg = 1.4eV at typical film thicknesses of 500–600 nm with absorber bulk defect density 1014 cm−3 and interface recombination velocity 100 cms−1. Moreover, the cell displays significant efficiency of 20–24% even at higher defect densities, emulating degraded absorber film quality. Thus from the comprehensive study presented here, it is quite evident that MAGe0.75Pb0.25I3 indicates a pathway to approach the SQ limit in terms of efficiency for perovskite solar cells.