Carboxylic Acid-Based Hole Transport Layer with Both Anchoring and Passivation in Inverted Perovskite Solar Cells

Abstract

The hole transport layer (HTL) plays a pivotal role in the performance of inverted perovskite solar cells (PSCs), especially in carrier transport, anchoring to the substrate as a buried interface, and defect passivation. Novel HTLs that simultaneously achieve indium tin oxide (ITO) substrate anchoring, passivation of buried perovskite defects, and favorable interfacial energy alignment are seldom addressed. In this work, we designed a novel HTL (denoted as TPCOOH), which is functionalized with dicarboxylic acid groups in the central phenyl ring, which can anchor onto ITO substrates and passivate the top perovskite, as well as coupling with methylthio-substituted triphenylamine and thiophene units to generate suitable energy alignment and transfer the hole, realizing both passivation and anchoring effects. TPHex, as a control, had dihexyl substitution in the center. Inverted PSC devices based on TPCOOH and TPHex as hole transport layers (0.1 cm2) achieved power conversion efficiencies of 24.68% and 23.72%, respectively. The improved efficiency of TPCOOH-based devices is attributed to suppressed nonradiative recombination, rapid interfacial charge transfer, and minimal energy loss due to well-matched energy levels. These improvements are ascribed to the carboxyl groups in TPCOOH, which anchor to ITO, thus ensuring better film coverage and improved charge transport, while the passivation functionality simultaneously mitigates perovskite defects. Notably, the TPCOOH and TPHex devices retain 75% and 65% of their initial power conversion efficiencies (PCEs) after 1200 h of thermal aging at 65 ± 5 °C in a nitrogen atmosphere.