Thermally stable inverted perovskite solar cells using an electropolymerized Zn-porphyrin film as a dopant-free hole-transporting layer

Although perovskite solar cells (PSCs) have achieved remarkably high efficiency (25.7%), their long-term stability still needs to be addressed for commercial applications. As an important part of PSCs, the hole-transporting layer (HTL) plays a crucial role in the overall device performance. Zinc porphyrin (ZnP) has excellent thermal/chemical stability, which is beneficial for enhancing the stability of PSCs when it is used as the HTL. In addition, the strong hydrophobicity of the electropolymerized film surface is believed to suppress heterogeneous nucleation and thus improve the quality of the resulting perovskite film. Herein, we have utilized the electropolymerized ZnP (PZnP) to fabricate the dopant-free HTL without annealing. The MAPb(CI_0.05I_0.95)₃ PSCs based on PZnP presented a record-high power conversion efficiency (PCE) of 19.75%, which was significantly improved as compared to the previously reported best result of 16.7% with electropolymerized HTL. The unencapsulated PSCs sustained around 70% of the initial efficiency after thermal aging at 85 °C for 480 h, while the PTAA-based PSCs showed a 78% decrease in the initial PCE under the same conditions. Moreover, the long-term stability of the electropolymerized film-based PSCs was exceptional, retaining about 96% of the initial performance over 5000 h. The electropolymerization strategy provides an effective approach for developing cost-effective dopant-free HTL for thermally stable and efficient PSCs.