The effect is considered of order and disorder on the electrical and optical performance of ionic oxide semiconductors used to produce optoelectronic devices such as p–n heterojunction solar cells and thin-film transistors (TFTs). The results obtained show that p-type c-Si/a-IZO/poly-ZGO solar cells exhibit efficiencies above 14% in device areas of about 2.34 cm2, whereas amorphous oxide TFTs based on the Ga–Zn–Sn–O system demonstrate superior performance to the polycrystalline ZnO TFTs, with I ON/I OFF ratio exceeding 107, turn-on voltage below 1–2 V and saturation mobility above 25 cm2 V−1 s−1. In addition, preliminary data on a p-type oxide TFT based on the Zn–Cu–O system are presented.