Bruno Ehrler

The low bandgap of mixed lead–tin perovskites makes them promising candidates for multijunction perovskite solar cells. However, their inferior stability limits their potential. Here, we study the degradation of devices during the first day of operation. We continuously illuminate devices with either poly(3,4-ethylenedioxythiophene):poly(styrenesulfonate) (PEDOT:PSS) or (2-(9H-carbazol-9-yl)ethyl)phosphonic acid (2PACz) hole-transport layers for 12 h at open or short circuit and track their performance using current–voltage and impedance measurements. We subsequently track the recovery of the devices in the dark. We find a permanent burn-in degradation, and multiple ionic processes. Under both aging conditions, ionic field screening decreases the current in both types of devices. After aging at open circuit, the performance fully recovers in the dark, but after aging at short circuit, we observe more permanent degradation and further decrease of the performance in the dark, which we ascribe to trap formation caused by prolonged ion accumulation at the interfaces.

Metal halide perovskite solar cells have considerable potential for next-generation solar power production. However, if not controlled, the migration of mobile ions can hamper the stability of perovskite solar cells. Intensive research efforts have devised methods of suppressing ion migration and degradation in perovskite materials, resulting in solar cells that are stable over thousands of hours during accelerated ageing testing. Here, we review the chemical origins of ion migration, its effect on material and device performance and stability, and strategies to mitigate its impact. Ion migration originates in the soft lattice of the halide perovskite framework and its low defect-formation energy, but there are many different strategies to reduce its effects, from compositional engineering of materials and device architecture changes to additives and strain engineering. The field has made great progress in understanding the origin and properties of mobile ions in halide perovskites and has improved operational stability beyond expectations. Nonetheless, there are still ample opportunities to further improve the long-term durability of perovskite solar cells, either by reducing ion migration or its effect on solar cell efficiency.

Intensity-modulated photoluminescence spectroscopy (IMPLS) is a frequency-domain, fully optical technique that probes ionic processes in halide perovskites.

Mobile ions play a key role in the degradation of perovskite solar cells, making their quantification essential for enhancing device stability. Various electrical measurements have been applied to characterize mobile ions. However, discerning between different ionic migration processes can be difficult. Furthermore, multiple measurements at different temperatures are usually required to probe different ions and their activation energies. Here, we demonstrate a new characterization technique based on measuring the thermally activated ion current (TAIC) of perovskite solar cells. The method reveals density, diffusion coefficient, and activation energy of mobile ions within a single temperature sweep and offers an intuitive way to distinguish mobile ion species. We apply the TAIC technique to quantify mobile ions of MAPbI₃ and triple-cation perovskite solar cells. We find a higher activation energy and a lower diffusion coefficient in the triple-cation devices. TAIC measurements are a simple yet powerful tool to better understand ion migration in perovskite solar cells.

This 6th annual Emerging PV Report surveys peer‐reviewed advances since August 2024 across perovskite, organic, kesterite, matildite, antimony seleno‐sulfide, selenium, and tandem solar cell architectures. Updated graphs, tables, and analyses compile the best‐performing devices from the emerging‐pv.org database, benchmarking power conversion efficiency ( PCE ), flexible photovoltaic fatigue factor ( F ), light‐utilization efficiency ( LUE ), and stability‐test energy yield (STEY) against detailed‐balance efficiency limits as functions of photovoltaic bandgap, and average visible transmittance ( AVT ) for (semi‐)transparent devices. Beyond efficiency, operational stability is assessed via degradation rates ( DR ) and t ₉₅ lifetimes. Highlights include single‐junction perovskite cells with efficiencies above 27%, organics surpassing 20%, and new Si/perovskite tandems exceeding 34%. Although multiple record efficiencies have been achieved this year, advances in mechanical robustness and operational stability remain inconsistent, especially in complex tandem stacks, emphasizing the urgent need for standardized protocols, improved large‐area homogeneity, and database‐driven benchmarks to accelerate the transition from laboratory demonstrations to scalable, real‐world deployment.