An efficacious multifunction codoping strategy on a room-temperature solution-processed hole transport layer for realizing high-performance perovskite solar cells

A multifunctional carrier transport layer favoring outstanding carrier extraction, high-quality active layer formation, and a facile low-temperature process for efficient and large-scale perovskite solar cells (PSCs) are highly desirable. While co-doping approaches have recently become a hot topic in carrier transport layers to address the negative effects and limitations of typical single doping and further boost the carrier extraction properties and thus device performances, high-temperature, high power, and multi-steps processes/treatments are required which hinder their applications and potentially damage underneath structures particularly in emerging flexible electronics. In this work, we demonstrate the first kind of room-temperature solution-processed and post-treatment-free Li and Cu codoped NiOx nanoparticle-based hole transport layer (HTL). Simultaneously, the Li and Cu codoped NiOx HTLs show the interesting and critical features of (1) improved electrical conductivity and optical transmittance, (2) a high quality (pin-hole/crack free, compact and uniform) film morphology, (3) favoring large grain-size perovskite film formation, and (4) wide-range thermal stability up to 250 °C. With these interesting multiple functions, PSCs with Li and Cu codoped NiOx HTLs achieve a PCE of 20.8% and 18.2% on rigid and flexible substrates, respectively. This work contributes to a promising route for realizing highly efficient and stable rigid and flexible PSCs using abundant low-cost inorganic HTLs.