Low-pressure hot isostatic pressing for the fabrication of carbon electrode-based hole-transporting material-free perovskite solar cells

The reliance on expensive metal electrodes has been a major barrier to the commercialization of perovskite solar cells (PSCs). Metal electrodes can only be deposited on PSCs through a batch-to-batch thermal evaporation process, which is incompatible with scalable fabrication processes essential for commercial production. On the other hand, carbon electrodes (CEs), specifically those made from graphite and carbon black, are low-cost and can be deposited using economical and facile methods such as doctor blading, screen-printing, and hot-pressing. Here, the feasibility of using a low-pressure hot isostatic pressing (HIP) to laminate carbon film onto a perovskite device stack to produce CE-based hole-transporting material-free (HTM-free) PSC was investigated. The carbon film was positioned on the caffeine-added methylammonium lead iodide (Caf-MAPbI₃) perovskite film produced using a thermally enhanced vacuum-assisted solution process (VASP). The device was then vacuum-sealed in a thermoplastic bag and pressed in a HIP chamber under various pressures and temperatures for 10 min. The HIP process uniformly laminated the carbon film, promoting its seamless bonding with the Caf-MAPbI₃ perovskite film at pressures of ≤10 MPa. A PSC achieved a champion power conversion efficiency (PCE) of 10.54 % with the optimized HIP pressure of 6 MPa and temperature of 125 °C.