Strengthening the Interface between Perovskite and Carbon-Electrode by the Thermoplastic Behavior of Hydroxypropyl Cellulose to Elevate the Efficiency and Reverse-Bias Stability of Photovoltaic Device

Abstract Manipulating the sophisticated interface between perovskite/carbon-electrode (PVSK/CE) remains as one of the key tasks for hole-conductor-free, CE-based perovskite solar cells (CPSCs). Herein, we explore the problem from the viewing angle of an organic binder (hydroxy propyl cellulose, HPC) that is usually utilized to make robust CEs. It is observed that, beyond the dispersion capacity to carbon materials, HPC shows thermoplastic behavior at around 150 °C, which causes the formation of compactly packed CEs. Adding polyethylene glycol (PEG) further strengthens the “cross-linking behavior” of HPC polymer chains and lowers the thermoplastic temperature down to 100 °C, which compromises the 2D-precursor molecule induced “in situ healing” strategy. The synergy between PEG-assisted thermoplastic behavior and the “in situ healing” strategy reduce the defects and the recombination risks, which optimizes the device efficiency from ∼16% to 20.64%. Furthermore, the PEG-assisted plasticization to HPC polymer helps to build a condensed PVSK/CE interface and provides effective immobilization to the movable ions at the interface, which then raises the breakdown reverse voltage from –4.0 to –7.1 V, adding to the robustness of the hole-conductor-free CPSCs.