Penetrated passivation strategy for carbon nanotube-based perovskite solar cells

The carbon-based perovskite solar cells (C–PSCs) have attracted a lot of interest because of their low cost of fabrication and long-term stability. However, sluggish charge transfer kinetics and inadequate contact between perovskite (or hole transport layer) and carbon film typically hindered the performance of the device. Conventional 2D perovskite layer for surface passivation based on spin coating could lead to a non-uniform 2D perovskite layer due to the dissolution of FA⁺ cations in isopropanol, undermining the interfacial contact of C–PSCs. Herein, carbon nanotubes (CNTs) were sprayed on the composite hole transport layer (HTL) of Spiro-OMeTAD and P3HT as top electrodes in C–PSCs. To improve the interfacial contact between CNT electrodes and HTLs and inhibit carrier recombination, a passivation agent of phenylethylamine iodine (PEAI) was added into the CNT paste and sprayed onto the HTL. According to thorough characterization, PEAI penetrated through the HTL and interacted with the perovskite film surface, forming uniform 2D perovskite layers that passivated the surface defects of 3D perovskite films. Because of the even 2D perovskite layer and compact interfacial contact, the C–PSCs with penetrated PEAI exhibited greatly enhanced photovoltaic performance, with the champion device achieving a power conversion efficiency (PCE) of 19.5 %, superior to those with directly spin-coated PEAI, which had a maximum PCE of 16.0 %. Furthermore, the device with penetrated PEAI exhibited optimized long-term stability due to the better passivation effect.