Hole selective nickel oxide as transparent conductive oxide

Abstract

Transparent conducting oxides (TCOs) are essential for manufacturing perovskite and heterojunction solar cells. Specifically, nickel oxide (NiO) is of interest because it exhibits hole-selective behavior in conjunction with Si. Additionally, the bandgap of about 3.6 eV allows high transmission even at wavelengths below 500 nm. However, NiO is not yet ready for industrial implementation in solar cells. This study guides a simple, industry-compatible way to fabricate transparent conductive NiO thin films by evaporation and postdeposition annealing. The crystallization behavior of NiO is investigated intensively. The lattice parameter of cubic NiO decreases with increasing annealing temperature, probably caused by the loss of oxygen. Resistivity and absorption measurements were done to assess the suitability of NiO as TCO. A minimum resistivity of about 50 Ω cm with a corresponding absorption coefficient of 19 × 103 cm−1 is reached using an annealing temperature of 400 °C. A p-n junction was formed consisting of n-doped Si and p conducting NiO to prove the hole selectivity of NiO.