A research team led by Prof. PAN Xu from the Hefei Institutes of Physical Science of the Chinese Academy of Sciences (CAS) have developed an optimized transport layer for inverted perovskite solar cells, achieving a breakthrough that enhances both device efficiency and stability.

The findings were published in Nature Materials.

Perovskite solar cells have achieved power conversion efficiencies close to 27%, positioning them at the forefront of next-generation photovoltaic research. Previously, the research team developed a novel strategy to homogenize cation distribution within the perovskite absorber layer, offering a new pathway for absorber optimization. In addition to the absorber, the semiconductive transport layers play a critical role in charge separation and transport. Among them, [6,6]-phenyl-C61-butyric acid methyl ester (PCBM) is widely used as an electron transport material, but it readily forms dimers under light and heat. This leads to reduced charge mobility, efficiency loss, and accelerated degradation, posing a major challenge for practical applications.

To address this issue, the researchers analyzed the stacking behavior of PCBM molecules on different perovskite surface terminations. They identified molecular orientation heterogeneity as a key factor promoting dimer formation.

Based on this finding, the researchers designed a PCBM precursor additive, 2,3,5,6-tetrafluoro-4-iodobenzoic acid (FIBA), which interacts with PCBM molecules, guiding their ordered stacking on the perovskite surface and homogenizing molecular orientation. This alignment suppresses the topological matching necessary for the cycloaddition reaction, which effectively inhibits dimer formation.

Using this strategy, the researchers achieved impressive device performance. They achieved 26.6% efficiency for small-area cells (approximately 0.1 cm²), 25.3% for single-cell devices (1 cm²), and 21.3% for large-area modules (762 cm²). Additionally, the optimized devices demonstrated exceptional stability, maintaining over 85% of their initial efficiency after 2,000 hours of continuous operation under combined heat, humidity, and light stress conditions.

This work provides a practical and effective approach to improving the efficiency and stability of perovskite solar cells simultaneously.

This work was supported by the Youth Team Program for Stable Support of Basic Research of CAS, the National Key R&D Program of China, and the National Natural Science Foundation of China.