Publication date: 17th February 2025
Flexible perovskite solar cells (PSCs) are gaining attention for wearable and transferable devices, requiring a low-temperature processed electron transport layer (ETL). The fullerene C60 is commonly applied as the electron transport layer (ETL) in high-efficiency metal halide perovskite solar cells and has been found to limit their open circuit voltage due to the energetic offset and defect formation in the perovskite/C60 interface.
In this study, to address this, a thin lithium fluoride (LiF) interfacial layer was introduced as a buffer layer and efficient hole blocker. Researchers reported about the moderate dipole effect and most likely the presence of fixed charges of a LiF interlayer at the interface, that lowered the concentration of holes close to the perovskite/C60 interface, and helped to improve the energetic offset as well as the suppression of the interfacial defects.
Here in, we fabricated flexible PSCs with a device architecture of PET/ITO/PTAA/Perovskite/LiF/C60/AZO/Ag. The RbCsMAFA perovskite phase formation was confirmed through X-ray diffraction (XRD), X-ray Photo Electron Spectroscopy (XPS), Photoluminescence (PL), and absorbance analyses. Further the Perovskite/LiF heterojunction charge carrier dynamics were characterized through Time Resolved Photo Luminescence (TRPL) spectroscopy. It was confirmed the better charge transfer in Perovskite/LiF interface compared to pristine Perovskite from 77.2 ns to 24.6 ns. The addition of LiF improved the device power conversion efficiency (PCE) from 12.11% to 16.35% and from 7.68% to 9.29% over small (device active area 0.25 cm2) and large areas (device active area 2 cm2), respectively. Additionally, the Electrochemical Impedance Spectroscopy (EIS), conductivity measurements using electron-only devices, and Urbach analyses from External Quantum Efficiency (EQE) spectra suggested about the reduction of non-radiative recombination losses. These devices also showed excellent environmental stability, maintaining 70% efficiency after 2000 hours. This improvement can be attributed to efficient electron extraction and reduced charge recombination at the interfaces. Regarding flexibility, the devices retained their PCE even after 1000 bending cycles, demonstrating excellent mechanical stability. This approach demonstrates that incorporating a LiF interfacial layer can enhance the performance and durability of flexible, low-cost PSCs.
T.D. acknowledges the SVMCM scholarship (Grant No.WBP221666168821 of 2022) funded by the Government of West Bengal for research support. AG sincerely acknowledges the
DST-FIST program, Govt. of India (SR/FST/College-2017/53 (C)), SERB, Govt. of India for the Start-up Research grant (SRG/2019/000318) and UGC-DAE CSR (CRS/2021 22/04/603) for supporting this work
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