Improving the efficiency and stability of perovskite solar cells through optimization of the hole-transport layer

Perovskite solar cells (PSCs) have emerged as a leading technology in the photovoltaic sector due to their high efficiency and low fabrication cost. However, the performance and stability of PSCs are often limited by the properties of hole transport layers (HTLs). In this study, we explore the use of cobalt phthalocyanine (CoPc) and a composite CoPc/Spiro-OMeTAD layer as HTLs to enhance the efficiency and stability of PSCs. Structural analysis via AFM revealed that the CoPc/Spiro-OMeTAD composite layer possesses a uniform, pinhole-free surface morphology, crucial for minimizing charge recombination. Optical studies demonstrated that these composite layers maintain high transparency while providing effective light absorption. Photoelectrical characterizations showed that PSCs with the CoPc/Spiro-OMeTAD HTLs achieved a power conversion efficiency (PCE) of 18.7 %, outperforming devices with standard Spiro-OMeTAD and single CoPc layers. Moreover, the composite HTLs improved the stability of the PSCs, retaining 84 % of the initial PCE after 300 hours of operation without encapsulation. Impedance spectroscopy indicated that the composite HTLs reduce series resistance and charge transfer resistance of the devices. These findings suggest that CoPc/Spiro-OMeTAD composite layers are promising candidates for enhancing both the efficiency and stability of PSCs.