NiO nanosheets as efficient top hole transporters for carbon counter electrode based perovskite solar cellsElectronic supplementary information (ESI) available: EDX spectra of NiO nanosheet based devices, device performance distribution, equivalent circuit and EIS data of devices, BET of NiO powder, transient photovoltage decay measurement data of devices. See DOI: 10.1039/c5ta06458a

Herein, we present fully printable carbon electrode based perovskite solar cells using highly crystalline NiO nanosheets as top hole transport layers, mesoporous TiO 2 nanoparticles as a bottom electron transport layer and ZrO 2 as an intermediate spacer layer, respectively. Time-resolved photoluminescence decay measurements, electron impedance spectroscopy and transient photovoltage decay measurements have revealed that the NiO nanosheets as top hole transporters exhibit superior charge collection efficiency and a prolonged charge lifetime. As a result, an impressive power conversion efficiency of 14.2% is achieved under standard testing conditions. Herein, highly crystalline NiO nanosheets are reported as top hole transporters in fully printable carbon electrode based perovskite solar cells to enhance device performance.