The Rise of Perovskite Solar Cells and the Challenges Ahead

Perovskite solar cells (PSCs) have emerged as a groundbreaking photovoltaics (PV) technology, based on metal halide perovskites (MHPs) such as methylammonium or formamidinium lead iodide (MAPbI3 or FAPbI3, respectively). MHPs possess several desired characteristics for PV absorbers, including a direct bandgap with a strong absorption coefficient, long carrier lifetime and diffusion length, low defect density, and easy tuning of composition and bandgap.

In 2009, MHPs were first reported as a sensitizer in a dye cell configuration based on liquid hole-conducting electrolyte. Since then, the efficiency of single-junction PSCs has soared to a certified 25.2%. Most high-efficiency PSCs are fabricated through solution processing, making PSCs an attractive, potentially high-performance, and low-cost PV technology.

Various deposition approaches have been developed for scaling up PSCs, leading to a recent demonstration of an 802-cm2 perovskite solar module with a certified 16.1% efficiency. This module performance is rapidly approaching that of established thin-film PV technologies such as CdTe and CIGS. PSC stability has also seen significant improvements in recent years through optimization efforts and encapsulation strategies.

Despite their impressive progress, PSCs still face several challenges:

1. Stability: Achieving long-term stability under outdoor operating conditions remains a major target. Understanding degradation mechanisms and tailoring standard packaging/encapsulation schemes for perovskites is crucial.
2. Scaling Up: The performance gap between small-area cells and larger modules is larger than predicted, due to factors such as nonuniform coating and interconnection structure limitations. Scalable fabrication processes must be adopted to incorporate cell-level improvements.
3. Efficiency: Increasing open-circuit voltage and fill factor through interface engineering and defect reduction is essential. The incorporation of Sn into Pb-based perovskite could increase short-circuit current density, but Sn-induced defects and stability issues are more challenging.
4. Toxicity: High-efficiency PSCs contain toxic Pb, which could pose challenges for commercialization. The impact of Pb on the environment and humans must be carefully evaluated, and strategies for preventing Pb release should be developed if it remains indispensable for PSCs.

In conclusion, perovskite solar cells hold great promise as a potential PV technology for terawatt-scale energy production. As researchers continue to address the remaining challenges, the future of PSCs looks bright, paving the way for a more sustainable and efficient solar-powered world.