Functionalized CNTs as Effective Additives to Improve the Efficiency of Perovskite Solar Cells

High-quality and uniform perovskite films are the first step toward high-performance perovskite solar cells (PSCs). Adding additives to regulating the film formation process is proved to be an efficient way to acquire high-quality perovskite films. In this study, we use functionalized carbon nanotubes (CNTs) as effective additives to improve the power conversion efficiency (PCE) of PSCs. Three kinds of CNTs, namely, pristine CNTs, amino-group-functionalized CNTs (NH2-CNTs), and carboxyl-group-functionalized CNTs (COOH-CNTs) are selected. The PCE of PSCs doped with pristine CNTs (13.91%) drops compared with that of a control device (16.56%), while the PCE increases to 17.47% for NH2-CNT-doped PSCs and 17.75% for COOH-CNT-doped PSCs. A detailed study shows that both NH2-CNTs and COOH-CNTs can facilitate the crystallization of the perovskite films. Compared with a control film, the hole mobility of the perovskite films can be increased by 1 order of magnitude in a COOH-CNT-doped perovskite film. This contributes to better carrier transportation in PSCs. After optimizing the length and doping concentration of the COOH-CNTs, the PCE for PSCs doped with COOH-CNTs steadily improves to 18.68%. Furthermore, the stability of PSCs has also been improved with COOH-CNT-doped perovskite films. Our study provides insightful hints for using functionalized carbon-based materials to develop high-performance perovskite-based optoelectronic devices.