Photovoltaic effects in CdSe quantum dot (QD) films have been studied using surface photovoltage spectroscopy and complementary methods. The results show that, contrary to previous studies, nonnegligible electric fields can exist in QD films. As a result, driftlike currents must be considered, in addition to the well-known diffusionlike currents. However, it is found that the specific case of photovoltage sign reversal, observed after etching highly quantized CdSe QD films, is governed by diffusionlike transport. The latter is highly influenced by preferential trapping of one type of charge carrier. The preferential trapping is shown to be surface localized and is strongly ambient dependent. It is shown that the photovoltaic properties of these CdSe QD films are dominated by their surface state distribution.

Surface photovoltage spectroscopy (SPS) is used to determine the position of the deep defect state levels in undoped hydrogenated amorphous silicon (a-Si:H). The occupied and the empty levels, and their nature, are identified with a clear advantage over existing methods. The identification of the levels and the effect of light soaking on their concentration provides direct experimental confirmation of the main features predicted by thermal equilibrium models. The finding of other levels in a-Si:H materials of larger disorder further supports the recently proposed potential fluctuations model.

No abstract

No abstract