Small Molecular Organic Hole Transport Layer for Efficient Inverted Perovskite Solar Cells

To commercialize perovskite solar cells (PSCs), it is crucial to develop cost-effective, dopant-free hole transport layers (HTLs) that can be processed at low temperatures. Herein, a dopant-free small molecular material 4,4′,4′-Tris[2-naphthyl(phenyl)amino]triphenylamine (2TNATA) was utilized in inverted PSCs as a HTL. The position of the highest occupied molecular orbital energy of 2TNATA is properly aligned with the perovskite valence band maximum. Moreover, 2TNATA can be processed at lower temperatures and shows excellent thermal stability. The lead (Pb) perovskite on 2TNATA exhibited superior crystallinity and morphology compared to the perovskite on poly(3,4-ethylenedioxythiophene) polystyrene sulfonate (PEDOT:PSS) and poly[bis(4-phenyl)(2,4,6-trimethylphenyl)amine] (PTAA). Furthermore, the carrier kinetics in 2TNATA-based PSCs was superior to PTAA and PEDOT:PSS-based PSCs. Consequently, an outstanding power conversion efficiency (PCE) of 20.58% was observed from the 2TNATA HTL-based 0.09 cm² PSCs, while PTAA and PEDOT:PSS HTLs-based 0.09 cm² PSCs showed PCE of 19.36% and 14.35%, respectively. Moreover, the 2TNATA HTL-based 1.0 cm² PSCs demonstrated an impressive PCE of 20.04%. The results indicate that 2TNATA might be a promising HTL for the inexpensive and efficient inverted PSCs.