In a remarkable leap forward for solar technology, researchers have unveiled a novel approach to enhancing the stability and efficiency of halide perovskite solar cells—a material rapidly emerging as a promising competitor to traditional silicon photovoltaics. Published in the prestigious journal Science, the study details a breakthrough method that accelerates the formation of the coveted black phase crystal structure of formamidinium lead iodide perovskites at lower temperatures. More importantly, this new technique significantly impedes the degradation of the material into its inert yellow phase, a persistent challenge that has long hindered the commercial viability of perovskite-based solar cells.
Halide perovskites have attracted widespread attention due to their solution-processable nature, which allows them to be fabricated via relatively low-cost techniques, including solution deposition or vapor-phase methods. However, the Achilles’ heel of perovskite photovoltaics has been their structural instability, whereby the optimal photovoltaic black phase transforms into a non-functional yellow phase over time, especially under heat and illumination stress. This phase shift undermines the performance and longevity of solar cells built with these materials, limiting their practical application despite their impressive initial efficiencies.
The team from Rice University, led by chemical engineer Aditya Mohite, pioneered a strategy that integrates two critical additives into the perovskite precursor solution: a two-dimensional (2D) perovskite template and formamidinium chloride. This synergistic combination regulates crystallization dynamics and induces compressive strain within the crystal lattice, fostering an environment where the black perovskite phase forms more rapidly, even at reduced thermal budgets. Furthermore, the additives fortify the structure against phase degradation, dramatically enhancing the film’s resilience against environmental aging.
Central to this advance is the nuanced understanding of the formamidinium lead iodide crystal architecture. The crystal lattice comprises lead-iodide octahedra—each with a lead atom enveloped by six iodine atoms—arranged in a three-dimensional corner-sharing configuration. This particular geometry is essential for effective electronic coupling and optimum solar absorption. The crystalline voids, known as A-sites, are occupied by positively charged formamidinium ions, which although slightly oversized, ideally maintain the lattice’s open configuration that results in the black, light-absorbing phase.
Ordinarily, this imperfect ionic fit causes the crystal to collapse into a denser phase where octahedra share faces rather than corners. This distortion drastically impedes the material’s ability to absorb sunlight, shifting its appearance from deep black to pale yellow, and effectively rendering it inert for photovoltaic applications. Overcoming this instability typically requires high-temperature annealing (~150 °C) to expand the lattice and accommodate the formamidinium ions, which unfortunately does not guarantee permanent retention of the black phase once cooled.
By embedding 2D perovskite sheets within the precursor mixture, these layered structures act as architectural templates, guiding the subsequent growth of three-dimensional crystals in a manner that accommodates the formamidinium cations more effectively at lower temperatures. This templating effect is likened to placing marbles into a prearranged grid of holes, spatially organizing the crystal formation and yielding larger, better-oriented crystals with fewer defect-prone surfaces.
Formamidinium chloride plays a pivotal complementary role by replacing a portion of the iodide ions with chlorine, which has stronger bonding affinity with lead. This substitution enhances the corner-sharing connectivity of the octahedra, promoting a stepwise, energetically favorable crystallization pathway. Such a gradual transition is vital for uniform crystal growth, preventing abrupt structural changes that could introduce defects or unwanted phases.
Intriguingly, the study reveals that chlorine not only aids crystallization but also fundamentally alters the degradation pathway of the perovskite films. Traditional degradation follows a low-energy chemical route culminating in the formation of the yellow phase. However, with chlorine integrated into the lattice, the degradation process is forced onto a much higher-energy pathway. This shift dramatically slows the breakdown of the material and effectively bypasses the undesirable yellow phase, instilling unprecedented durability.
The dual additive approach also confers improved moisture and thermal resistance by producing films with larger crystal domains and favorable orientation. Larger crystals possess fewer grain boundaries and surface defects, which are typical initiation sites for environmental degradation. This structural refinement, combined with the chemical stabilization imparted by chlorine, resulted in perovskite films that preserved 98% of their photovoltaic efficiency after 1,200 continuous hours of accelerated aging tests at elevated temperatures around 90 °C.
This breakthrough was facilitated by sophisticated degradation testing apparatus engineered by Rice doctoral alumnus Faiz Mandani. Unlike earlier setups that could monitor only single devices, the newly devised chamber can uniformly expose up to 100 solar cells to controlled heat and light simultaneously. This high-throughput capability allows comprehensive statistical analysis of device longevity and degradation mechanisms, providing invaluable insights that underpin the reported findings.
The collaboration underpinning this advancement spanned multiple institutions and continents, reflecting the international nature of cutting-edge materials science. Partnerships with scientists at Lawrence Berkeley National Laboratory, the University of Rennes in France, the University of Lille, University of Cambridge, and Northwestern University created a vibrant research ecosystem where experimental rigor and theoretical insights converged to tackle one of photovoltaics’ most persistent problems.
Rice University’s Mohite group, recognized globally for its expertise in perovskite photovoltaics, highlights the broader impact of this research. The innovative stabilization strategy not only paves the way for durable perovskite solar cells but also propels forward the development of tandem solar cells combining silicon and perovskite layers, which have demonstrated module efficiencies exceeding 35%. Such high-performance tandem cells could play a transformative role in sustainable energy, directly impacting electricity generation and enabling solar-driven chemical processes like green hydrogen production.
Funded by prominent agencies including the U.S. Department of Energy, the U.S.-India Educational Foundation, and the National Science Foundation, this work exemplifies how multidisciplinary and multinational scientific convergence accelerates the path toward practical renewable energy technologies. The research community anticipates that the insights reported in this study, particularly the dual-faceted approach of crystallization control and degradation pathway modification, will inspire new materials design principles and forge the way for perovskite solar cells with unprecedented stability and efficiency.
Subject of Research: Halide perovskite stabilization for photovoltaic applications
Article Title: Bypassing the yellow phase for extremely stable formamidinium lead iodide perovskite solar cells
News Publication Date: 30-Apr-2026
Web References:
DOI link: 10.1126/science.aeb7992
Rice University Rice News: news.rice.edu
References:
Garai, R., Metcalf, I., Nandi, N., Ahlawat, P., Reyes-Suárez, B., Mandani, F., et al. (2026). Bypassing the yellow phase for extremely stable formamidinium lead iodide perovskite solar cells. Science, DOI: 10.1126/science.aeb7992.
Image Credits: Photo by Jorge Vidal/Rice University
Keywords
Perovskites, Photovoltaics, Crystallization, Stability, Solar Cells, Formamidinium Lead Iodide, Chlorides, Degradation Pathways, Two-Dimensional Perovskite, Chemical Engineering, Renewable Energy, Tandem Solar Cells
Tags: advanced additive engineering in photovoltaicscommercial viability of perovskite solar cellsformamidinium lead iodide perovskiteshalide perovskite black phase formationheat and illumination stress resistance in solar cellslow-temperature perovskite crystallizationperovskite phase transition controlperovskite solar cells stability enhancementRice University solar researchsolar cell longevity improvementsolution-processable photovoltaic materialsyellow phase degradation prevention
