A robust and thickness-insensitive hybrid cathode interlayer for high-efficiency and stable inverted organic solar cells

High efficiency and stability, low-cost and large-area solution processing are critical for the commercialization of organic solar cells (OSCs), and there are still great challenges to develop an appropriate cathode interlayer (CIL) for efficient and stable large-area OSCs. Herein, by ingeniously combining a cross-linkable interfacial polymer (PFOPy) and a n-type self-doped interfacial molecule (PDINN), a robust and thickness-insensitive hybrid CIL (PFOPy-N) is developed to enable high-efficiency and stable inverted OSCs. The PFOPy-N CIL shows strong solvent resistance properties due to the crosslinking characteristic of PFOPy. Moreover, the PFOPy-N CIL achieves significantly increased electrical conductivity due to the n-type self-doping characteristic of PDINN and the charge transfer between PFOPy and PDINN and simultaneously offers a further reduced work function of ITO, which synergistically enhances charge transport and extraction and reduces charge recombination in inverted OSCs. Consequently, inverted OSCs based on the PFOPy-N CIL (10 wt% PDINN) show significantly improved photovoltaic performance compared to pure PFOPy and PDINN based devices as well as ZnO based devices. Utilizing a PM6:L8-BO active layer, an optimal PFOPy-N based device exhibits an outstanding PCE of 17.65%, which is one of the highest values for inverted OSCs with an organic cathode interlayer. The PFOPy-N based devices with the CIL thickness range of 7 to 39 nm all exhibit high PCEs of over 15.06%, showing obviously increased thickness insensitivity. PFOPy-N based large-area and flexible devices also exhibit superior PCEs of 15.95% and 15.84%, respectively, indicating the great potential of the PFOPy-N CIL in large-area and flexible OSCs. Notably, the PFOPy-N based device possesses significantly higher thermal cycling stability compared to the ZnO based device, indicating the robust resistance of the PFOPy-N CIL to thermal cycling stress. The impressive results will inspire the simple and effective strategy of combining crosslinking and self-doping characteristics to develop robust and thickness-insensitive hybrid CILs for high-efficiency and stable OSCs.