Lead-based organic-inorganic perovskite photovoltaic architectures have demonstrated remarkable advancement, with certified record power conversion efficiency (PCE) of single-junction research cells increasing from 14.1% in 2013 [4] to 26.7% in 2024 [5] (27.0% in January 2025 according to NREL, 2025). The gap between perovskite solar cell (PSC) and silicon single-junction cell efficiencies has thus narrowed significantly. However, translating these benchmark efficiencies to commercial-scale module production remains a critical challenge. [6]

One reason for upscaling difficulties is stability, influenced by both intrinsic and extrinsic degradation mechanisms. [7] While efficiency improvements have dominated research focus, attention is increasingly shifting towards enhanced stability and reliability to ensure stable long-term performance and reproducible results.

Given the exceptional efficiency of lead-based PSCs, concentrating research efforts on their stability appears compelling. However, lead toxicity presents significant concerns, endangering human health during fabrication and operation while posing a risk to environmental health if leakage occurs. Notably, lead can inflict neurological and renal damage even at minimal exposure levels. [8] While strategies to mitigate lead-associated risks exist [9], the ultimate objective remains to completely eliminate lead from PSCs. This is crucial for increased safety, market acceptance and adherence to green chemistry principles. [10]

This review examines lead-free perovskite material stability, focusing on experimental outcomes and enhancement strategies. While advancing efficiency of lead-free PSCs remains crucial, parallel stability development is vital, as this dual focus promises photovoltaic technologies that balance efficiency with long-term operational stability.

Through a systematic literature assessment, close to 415 scientific publications were collected from Scopus and Web of Science using keyword clusters related to perovskite photovoltaics, stability and lead-free materials with a publication time range from 2020-2025.

Tin-based PSCs represent the most promising lead alternatives, having achieved efficiency improvements from 0.9% in 2012 [11] to 15.7% in 2024 using FASnI₃ (FA: formamidinium) perovskite [12]. Other common tin-based compositions with suitable bandgaps for photovoltaics include CsSnI₃ and MASnI₃ (MA: methylammonium). [13]

The primary challenge for tin-based PSCs is oxidative degradation of Sn²⁺ to Sn⁴⁺, easily initiated due to low standard redox potential (+0.15V compared to +1.67V for Pb²⁺). [14] This degradation, accelerated by moisture contact, increases electron-hole recombination due to p-type self-doping. [15] Temperature also affects stability through phase changes, with FASnI₃ and CsSnI₃ outperforming MASnI₃ in thermal stability. [14]

Various stability enhancement strategies include additives preventing Sn²⁺ oxidation, grain boundary passivation, and 2D/3D structures. [16] A commonly-used additive SnF₂ reduces Sn vacancies and delays oxidation, though precise dosing is essential to prevent energy level mismatches. [17] Other effective additives include dipropylammonium iodide (DipI) with sodium borohydride (NaBH₄) as reducing agent, resulting in unencapsulated samples that retain 96% of initial PCE after 1,300 hours of continuous illumination at maximum power point (MPP) in nitrogen atmosphere. [18] Jiang et al. [2] passivated FASnI₃ using ethylenediammonium dibromide (EDABr₂), achieving 14.23% PCE, while encapsulated devices maintain 95% efficiency after 110h at MPP.

Double perovskites present another lead-free alternative, utilizing elpasolite structures with monovalent (M) and trivalent (T) B-site cations to form A₂MTX₆ or vacancy-ordered forms (A₂B0X₆, 0: vacancy). However, double perovskites face significant challenges, including large indirect bandgaps, low theoretical efficiency limits, severe instability and difficult synthesis, necessitating extensive compositional research. [19] Still, Chen et al. fabricated a Cs₂TiBr₆-based device with modest 3.3% PCE but exceptional stability, with no significant degradation observed during thermal stress (200°C, 24h, in N₂), moisture exposure (80% relative humidity, 6h), or continuous illumination (24h). [20]

In summary, our review demonstrates the growing attention of lead-free PSC development, with several options available, including Sn-based and double perovskites.