Efficient perovskite solar cells with negligible hysteresis achieved by sol–gel-driven spinel nickel cobalt oxide thin films as the hole transport layer†
Current–voltage hysteresis is a critical issue that impacts the photovoltaic performance of perovskite solar cells, and thus, it is imperative to develop high-efficiency perovskite solar cells without hysteresis behavior. Herein, we report the fabrication of efficient planar heterojunction perovskite solar cells employing solution-processed NiCo2O4 as the hole transport layer. The spinel NiCo2O4 thin film obtained via a sol–gel process exhibits high optical transparency, well-matched energy bands, smooth film morphology and decent electrical conductivity, much better than NiO, a typical hole transport layer for perovskite solar cells. We herein demonstrated that due to excellent hole extraction, transport, and collection properties of the solution-processed NiCo2O4, the device efficiency of up to 18.16% was achieved for the planar heterojunction perovskite solar cells. More importantly, the devices with NiCo2O4 as the HTL exhibited hysteresis-free behavior regardless of the voltage scan rate, which out-performed NiO-based devices.