Surface Polarity Regulation by Relieving Fermi-Level Pinning with Naphthalocyanine Tetraimides toward Efficient Perovskite Solar Cells with Improved Photostability

In perovskite solar cells (PSCs), defective perovskite grain boundaries (GBs) and/or surface due to photo-excitation and the resulted suboptimal carrier dynamics at the perovskite/charge transport layer, have largely limited further performance enhancement and aggravated the PSCs instability. Fundamentally preventing the formation of these trap-states through a simple and efficient approach is thus critical to the enhancement of both device performance and stability. Herein, a novel semiconductive silicon naphthalocyanine derivative (Cl-SiNcTI) to reduce the deep level trap states at the GBs and the surface of perovskite film is successfully employed via a newly proposed photon-relaxation mechanism. The resulting benign p-type surface polarity and suppressed non-radiation recombination lead to improved charge transport in bulk perovskite and at the perovskite/spiro-OMeTAD interface. With a synergistic contribution of the Cl-SiNcTI and 2-(2-Fluorophenyl)ethylamine iodide (oFPEAI), a 24.30% efficiency is achieved in a single cell with excellent operational stability. Moreover, under steady-state light illumination, 93% power output compared to its initial state can still be maintained after 250 h of continuous operation.