Mitigation of J-V distortion in CdTe solar cells by Ga-doping of MgZnO emitter

Distortions in the current-voltage curves of CdTe-based thin-film solar cells with MgZnO emitter layers are not uncommon. Even when such distortions are very subtle with standard sunlight, they can be greatly accentuated by the removal of short-wavelength photons with optical filters, and the dark-curve turn-on voltage can be noticeably increased. The strong suggestion is that good J-V curves with full-spectrum light often rely on photogeneration of electrons from trap states in the MgZnO emitter. When the carrier concentration of the CdTe absorber is increased with external doping, there is a corresponding need for a larger MgZnO carrier concentration. Based on the assumption that the emitter carrier concentration needs to be comparable to that of the absorber, Ga-doping of the MgZnO was shown to very nearly eliminate the large filtered-light distortions and is arguably superior to MgZnO that relies on photogeneration. In addition, it was shown that photogeneration and recovery in MgZnO is relatively slow, so that without Ga-doping, the cell efficiency improves gradually for most of an hour in the light, and the turn-on voltage of the dark curve increases on a similar time scale when the light is removed.

Automated summary

Distortions in the current-voltage curves of CdTe-based thin-film solar cells with MgZnO emitter layers may be present, especially when short-wavelength photons are removed with optical filters, resulting in a noticeable increase in the turn-on voltage of the dark curve. It has been shown that Ga-doping of MgZnO can nearly eliminate large filtered-light distortions, making it arguably superior to MgZnO that relies on photogeneration.