Low-temperature solution-processed Mg: NiOx hole transport layers for formal (n-i-p) perovskite solar cells

NiOx is one of the most promising inorganic hole transport materials for perovskite solar cells. However, lots of fabrication methods refer to NiOx are limited in n-i-p type perovskite solar cells. Because the deposition procedure of NiOx film such as polar solvents and high temperature process is seriously incompatible with perovskite light-absorption underlayers. In this work, highly crystalline NiOx nanocrystals are prepared using solvothermal method under the presence of long-chain oleylamine molecules. The resulted NiOx nanocrystals can be easily dispersed in weak-polar toluene and form films on perovskite layer without annealing procedure. The n-i-p type device with NiOx hole transport layer achieves an efficiency of 10.34%. Later, Mg2+ with different molar ratios are incorporated into the NiOx nanocrystals. It is found that introducing a certain amount of Mg2+ benefits to improve the ratio of Ni3+/Ni2+, thereby changing the work function and increasing the hole conductivity. As a result, the n-i-p type device with Mg-NiOx hole transport layer yields an improved efficiency of 12.41%.