Photoconductive NiOx hole transport layer for efficient perovskite solar cells

• Photoconductive NiO x -Pc was introduced through combining NiO x with phthalocyanine. • >300% increase in conductivity was observed in NiO x -Pc under illumination. • PSCs with NiO x -Pc exhibited > 21% efficiency with good thermal stability. 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.