The long road to outdoor stability: real-world challenges for controlling perovskite materials for solar cells

Abstract

Perovskite photovoltaics have demonstrated impressive performance in controlled laboratory tests, with power conversion efficiencies as high as 27%, positioning them as promising alternatives to conventional silicon-based solar cells for various applications. However, despite these major advances, operational stability remains a limiting factor for commercial applications. Large-scale implementation requires addressing challenges such as susceptibility to environmental stressors and the need for long-term outdoor stability, which few standardized outdoor testing studies and publications have accurately assessed. In this review, it is suggested that several stressors, such as temperature and irradiance fluctuations, UV-light, humidity, and precipitation have a significant relevance on the long-term stability. The main degradation reactions initiated by these stressors are reviewed for different compositions of perovskite absorbers and charge transport layers. Furthermore, we reviewed recent in situ and/or in operando studies of perovskite materials and devices under controlled conditions, which intend to elucidate reaction mechanisms and/or interactions among the device's layers in state-of-the-art perovskite compositions, which pave the way for a more rational design of stable devices and highlight the importance of developing in situ or in operando studies for each perovskite composition interacting with other materials within the cell stack. For controlling perovskite solar cells (PSCs) and improving outdoor stability, we emphasize strategies such as bulk modifications, interface engineering, and back electrode design, and discuss each specific strategy used in the literature that has been proved in outdoor conditions and its direct effect on device real-world stability. Moreover, additional strategies such as optimized interconnection layouts, protective functional layers, and advanced encapsulation materials are discussed. Additionally, in this work, an assessment of different measurement approaches aligned with international standards such as IEC 61215 and ISOS was carried out across different climate zones. Our analysis reveals a predominant focus on temperate climates in outdoor testing, along with growing interest in correlating indoor accelerated aging data with measured outdoor performance. In particular, tropical climates, with consistently high humidity, temperature, and solar radiation, provide an ideal setting for exhaustive and accelerated stability tests to evaluate strategies for improving perovskite devices. This review also emphasizes the need for expanding outdoor testing in diverse climates, particularly those enabling rapid feedback and decision-making, as a critical step towards ensuring PSC stability and commercial viability.