Photoconductive NiO_x hole transport layer for efficient perovskite solar cells

NiO_x is widely applied in perovskite solar cells (PSCs) as a hole transport layer. However, its poor conductivity limits the further improvement of device performance. Motivated by photoconductive phenomenon, here we propose a photoconductive NiO_x-Pc hole transport layer in PSCs through combining with phthalocyanine (Pc). Under illumination, Pc molecule absorbs light and will be excited. Then photogenerated charges on Pc molecule will transfer to NiO_x spontaneously and increase the hole density of NiO_x film, thus improving its conductivity. As a result, > 300% increase in conductivity is observed in NiO_x-Pc film and its conductivity reaches 4.6 * 10^-4 S m⁻¹. PSCs with NiO_x-Pc exhibit high efficiency of 21.68%, which is much higher than control devices (19.74%). In addition, device stability is also improved in PSCs with NiO_x-Pc and over 95%of initial efficiency is retained after 85 °C for 800 h.