Inverted perovskite solar cells (p-i-n structure) have emerged as a key technology in third-generation photovoltaics. These cells have garnered significant attention in the field of new energy due to their high energy conversion efficiency (PCE) exceeding 26%, compatibility with low-temperature solution methods and ease of device integration.
Researchers have continuously explored the development of new hole-transport materials and interface layers, as well as the optimization of perovskite crystal to significantly improve device efficiency and stability. However, electron transport materials (ETMs) are equally important for HTMs in devices, playing a decisive role in promoting the efficient transfer of electrons from the perovskite layer to the cathode. The development of high-performance ETMs remains highly challenging and is a key bottleneck restricting further progress in the field, as research on high-performance ETMs has significantly lagged behind that on HTMs.
Currently, fullerenes and their derivatives, especially C60, have become benchmark ETMs in inverted perovskite solar cells due to their excellent electron transport capabilities. Yet, the high-temperature vacuum evaporation processing method required for C60 greatly increases the complexity of device fabrication, severely hindering the pace of large-scale industrial production. While fullerene derivatives such as PCBM can be processed via solution methods, they suffer from some challenges such as high synthesis costs, poor interfacial stability, and phase separation under light and thermal stress, which directly affect device durability and lifetime. Therefore, designing efficient and stable non-fullerene ETMs is crucial for advancing the field of perovskite photovoltaics.
To address this challenge, a collaborative team including Professor Xugang Guo, Research Associate Professor Kui Feng, and Research Assistant Professor Qing Lian from the Department of Materials Science and Engineering at the Southern University of Science and Technology (SUSTech) conducted an in-depth analysis of the properties of representative non-fullerene ETMs. Through their research, they precisely identified the key characteristics required for high-performance ETMs. These included photothermal stability, low energy levels, high electron mobility, strong hydrophobicity, and multiple passivation groups. These properties are essential to meet the dual needs of efficient electron conduction and passivation protection of the active layer.
Based on these requirements, the team successfully developed a series of new non-fullerene ETMs based on cyano-functionalized fused bithiophene imide (CNI2), exemplified by PCNI2-BTI demonstrating outstanding performance.
Their work, titled “Non-Fullerene Electron Transporting Materials for High-Performance and Stable Perovskite Solar Cells”, has been published in Nature Materials.
Figure 1. Design concept of non-fullerene electron transport materials
The research findings indicate that PCNI2-BTI exhibits superior properties compared to the classic PCBM in several key aspects. It offers better photothermal stability, a more favorable vertical electron transport orientation, higher electron mobility and extraction efficiency, stronger hydrophobicity, and interfacial chelation effects. These advantages enabled perovskite solar cells based on PCNI2-BTI to achieve a maximum energy conversion efficiency of 26.0%. They also demonstrated excellent device operational stability under ISOS-L-3 test conditions, with a T80 lifetime approaching 1,300 hours—far exceeding that of devices based on PCBM.
This design strategy successfully guided the synthesis of multiple novel non-fullerene polymer ETMs based on CNI2. These materials enabled devices to reach energy conversion efficiencies of up to 26.1%, fully validating both the effectiveness and versatility of the design strategy.
This breakthrough has opened up a new path for the design of efficient and stable ETMs in perovskite photovoltaic devices and has propelled further development in the field.
Figure 2. Properties of electron transport materials and device performance
Research Associate Professor Kui Feng and Dr. Guoliang Wang from the University of Sydney are the co-first authors of the paper. The corresponding authors include Professor Xugang Guo, Research Associate Professor Kui Feng, Research Assistant Professor Qing Lian, and Professor Antonio Facchetti from Georgia Institute of Technology.
Paper link: https://www.nature.com/articles/s41563-025-02163-4
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