Intrinsic Acceptor-like Defects and Their Effect on Carrier Transport in Polycrystalline Cu₂O Photocathodes

Abstract

The disparity between theoretical estimate and experimentally achieved efficiency of Cu2O-based photovoltaic and photoelectrochemical devices is attributed to poor electrical transport in the material. Toward this, we study native point defects in single and polycrystalline Cu2O and their effect on charge carrier transport via temperature-dependent Hall measurement in a temperature range of 82–300 K. The temperature-dependent carrier concentration evinces the presence of two monovalent acceptors pertaining to VCu and VCusplit. We find that the second acceptor level lies ∼80 meV above the first acceptor and is active above ∼200 K temperatures only. Interestingly, the compensation ratio (ND/NA) decreases with the grain boundary cross section (ΛGB) of the sample, from 0.07 for the sample with ΛGB = 0.45 ×10–3 μm–1 to 0.02 for the sample with ΛGB = 0.22 × 10–3μm–1. In polycrystalline samples, carrier scattering at grain boundaries governs the hole transport at low temperatures (T < 150 K). However, trapping of holes by the acceptor-like intrinsic defects is the major factor affecting the high-temperature mobility in both single and polycrystalline Cu2O.