Highly efficient electron transport based on double-layered PC61BM in inverted perovskite solar cells

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Electron transport layer (ETL) plays a major role in determining performance of perovskite solar cells (PSCs). [6, 6]-phenyl C 61 butyric acid methyl ester (PC 61 BM) has been the preferred choice as the ETL in inverted PSCs. However, it has some drawbacks including current leakage, low mobility, and difficulty in full coverage of the perovskite layer with rough surface, resulting in charge recombination losses, charge leakage pathways and inefficient charge transfer at the perovskite/ETL, thus contributing to lower device efficiency and stability. For the first time, we introduce a simple strategy of implementing double-layered (DL) PC 61 BM as ETL to address the aforementioned challenges. The use of DL PC 61 BM particularly resulted in reinforced morphology of the ETL with reduced pin-holes and surface roughness compared to the single-layer (SL) PC 61 BM. This yielded increased electrical conductivity of the PC 61 BM, suppressed charge recombination, and facilitated higher number of charge generation, transfer/collection at the perovskite/PC 61 BM interface. Consequently, the DL PC 61 BM-based PSC delivered a considerable increase of power conversion efficiency (PCE) to 18.06%, which is much higher than the SL-based pristine PSC with 14.20%. Furthermore, the transition to DL from SL PC 61 BM exhibited longer ambient stability of the PSCs. This work can be easily adopted for other perovskite compositions. • A double-layered (DL) PC 61 BM is a simple strategy to improve the PSCs performance. • DL PC 61 BM ETL decreases the pinholes and smoothed the perovskite film. • Electrical conductivity, charge generation, and charge collection were increased. • DL PC 61 BM ETL reduces the charge leakage and recombination at the interface. • Significant enhancements in efficiency and stability could be obtained.