Piezo-effect and physics of CdS-based thin-film photovoltaics

We report a strong reversible piezo-effect in CdTe/CdS photovoltaics consistent with the piezo parameters of CdS. Our finding suggests a different understanding of CdS-based solar cells including CdTe- and CuIn(Ga)Se-based devices. Because the CdS film is put into compression in the device, the piezo coupling generates surface charges and the electric field opposing that of the absorber layer. The corresponding potential barrier makes CdS insulating and the device operate in a metal-insulator-semiconductor mode. Our understanding introduces the concept of piezo-photovoltaics and suggests specific practical implications. (c) 2005 American Institute of Physics.