Structure of Solids and Transition Metal Coordination Complexes

Case Study B
Many electronic and optoelectronic devices require high-performance p-type semiconductors
such as transparent conducting oxides (TCOs). For example, photovoltaics, solar water
splitting and light emitting diode (LED) devices would require p-type TCOs as transparent
electrodes for efficient hole collection and transport. However, p-type metal oxide
semiconductors are not as well investigated as their n-type counterparts. Of these oxides,
copper(II) oxide (Cu2O) is now being studied as a p-type TCO.
Cu2O crystallizes in a cubic structure (space group Pn−3m) with lattice parameter of 0.43 nm
in which the oxygen ions form a body-centered lattice, in which Cu ions are located in the
middle of two adjacent oxygen ions to form O–Cu–O dumbbell units. The direct band gap of
Cu2O is 2.17 eV, much smaller than that required for TCO applications and this with low hole
concentrations (