Performance enhancement of FASnI3 perovskite photovoltaic cell through gradient re-arrangement of bulk defect and distinct charge transport layers

This work deals with theoretical analysis of performance of a formamidinium tin iodide (FASnI₃) based perovskite solar cell. The advantages of using FASnI₃ over other perovskites include its low toxicity and environmental friendliness. While FASnI₃ has slightly lower thermal and moisture stability compared to the inorganic CsSnI₃, it offers better tunability of properties and higher power conversion efficiency (CE) potential. In PVSCs not only the surface defect but also the high concentration of Sn⁴⁺ creates huge bulk defect density inside the FASnI₃ and limits the CE. The bulk defect is of two types (1) fixed ionic defects due to Sn⁴⁺ and (2) mobile ionic defects due to Sn interstitial and halide vacancy. With a goal to overcome the impact of fixed defect, we used a technique to gradient distribution of Sn⁴⁺ mediated bulk defects inside the absorber. The PVSC: ITO/PEDOT: PSS/FASnI₃/C60/Au is simulated in OghmaNano where uniform distribution versus gradient distribution of defect inside FASnI₃ are analyzed. The ~ 10 to 13% rise in CE is observed for the gradient distribution of defect and is attributed to the enhancement in electric field inside the device. Moreover, the impact of mobile ions on the performance of both uniform and gradient PVSCs is comprehensively analyzed and reported in this work. The analysis indicates that an ion density up to the order of 10²² m⁻³ has no significant impact on the performance of the PVSC. In addition, considering the pivotal role of charge transport layers, seven different materials such as MoO₃, PEDOT: PSS, TCTA, V₂O₅, Li_0.05Ni_0.95O, SrCu₂O₂, and CuI are assessed for eligibility as HTAL in the proposed PVSC. Amongst those the CuI and C60 as HTAL and ETAL results in highest CE, FF, J_SC and V_OC of 20.64%, 69.09%, 1.14 V and 26.16 mA cm⁻² respectively. The reported photovoltaic device with high CE is environment friendly and may be a potential candidate for solar energy harvesting.