Design and Comparative Performance Analysis of High‐Efficiency Lead‐Based and Lead‐Free Perovskite Solar Cells

Abstract

Recently, the attention of photovoltaic (PV) community has been switched to a newcomer in the PV industry, namely the perovskite solar cells (PSCs) owing to their high power conversion efficiency (PCE), suitable band alignment, high diffusion length of charge carriers, and efficient photon absorption in the visible and near IR region of the electromagnetic spectrum. The continuing research efforts to improve the performance parameters of PSCs have improved the PCE from 3.9% in 2009 to a high value of 25.6% in 2021. [1,2] Even so, the commercialization of PSCs with the most popular absorber material, viz. CH 3 NH 3 PbI 3 (methyl ammonium lead iodide or MAPbI 3 ), is severely constrained as the entire perovskite absorber layer is chemically and thermally unstable due to the inherent instability of the organic cation present in it. One possible solution to improve the stability of the device is to replace the hybrid organic inorganic perovskite layer with an inorganic halide perovskite layer without affecting the charge extraction efficiency of the device. The current research effort in device architecture, materials, and interfaces makes the expected commercialization and use of PSCs very plausible and fascinating. Cesium (Cs) remains the best option for the unstable organic methyl ammonium (MA) cation in the widely used perovskite absorber material MAPbI 3 . Studies show that Cs incorporation in hybrid perovskites may increase thermal stability at temperatures above 100 C, optimise optical and electrical properties, control thermodynamic phase stability, finely regulate layer formation, and enhance device performance consistency. [3] Beyond Cs-doped hybrid perovskites, its fully inorganic counterpart, in which the organic part is totally replaced by Cs cation, also exhibits intriguing properties, which can be modified further to improve the interface between the active material and the neighboring transport layers of the device to enhance the transport of charge carriers. [4][5][6][7] A study shows that a highest PCE of 19.03% can be achieved with the device configuration FTO/TiO 2 /CsPbI 3 / SpiroMeOTAD/Ag when the popular but unstable transport layers TiO 2 and SpiroMeOTAD are employed with the CsPbI 3 absorber layer. [8] However, under optimum values of input parameters, a simulation study shows that a PCE of 21.4% for CsPbI 3 -based PSC with SnO 2 and Cu 2 O as transport layers can be achieved. [9] Even when the inorganic Cs-based lead halide perovskites exhibit comparatively good PCE, the toxic nature of lead (Pb) and the overall instability of the solar cell itself pose significant obstacles toward the large-scale commercialization of PSCs. [10] The substitution of nontoxic cations like Ge 2þ or Sn 2þ for poisonous Pb 2þ in inorganic Cs-based lead halide perovskites is one of the important steps toward the commercialization of PSCs. [11] Due to the intrinsic oxidation of Sn 2þ and Ge 2þ to Sn 4þ and Ge 4þ states, respectively, leading to device instability, computational modeling, and performance analysis o...

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