Effects of the Incorporation Amounts of C@NiO in Hole Transport Layer on the Performance of n-i-p Perovskite Solar Cells

The hole transport layer (HTL) plays an important role as a buffer layer in efficient n-i-p planar perovskite solar cells (PSCs). However, the 2,2 ',7,7 '-tetrakis[N,N-di(4-methoxyphenyl)amino]-9,9 '-spirobifuorene (Spiro-OMeTAD) HTL is easily affected by water and oxygen in the atmosphere due to the Li-TFSI additive, which causes morphological collapse and conductivity decrease of the HTL. Herein, an optimization strategy is realized via introducing NiO quantum dot-coated multiwalled carbon nanotubes (C@NiO) into the HTL for the performance improvement of PSCs. The effect of the C@NiO doping concentration on the photovoltaic performance of Cs(0.05)FA(0.81)MA(0.14)PbI(2.55)Br(0.45) (CsFAMA)-based PSCs was systematically studied. C@NiO with 0.015 mg mL(-1) effectively improves the compactness and conductivity of the HTM films. Simultaneously, C@NiO can effectively decrease the density of trapped states on the surface of perovskite, inhibiting carrier recombination in PSCs and promoting charge extraction between CsFAMA/Spiro-OMeTAD interfaces. As a result, PSCs with an appropriate concentration of C@NiO achieved a remarkably increased power conversion efficiency (PCE) from 19.13 to 22.50%. In addition, the optimized PSCs show excellent stability under various testing conditions, especially maintaining 91.3% of origin PCE after 1000 h without encapsulation in ambient conditions with high humidity (similar to 40% RH).