Piezo-photovoltaic effect in thin-film CdS/CdTE solar cells

We study pressure dependence of photovoltaic (PV) parameters in CdS/CdTe thin film solar cells, attributable to piezo-electric properties of the CdS layer. The significance of this piezo-PV coupling is that it reveals the indispensable effects of internal pressure developing in the device as a result of its deposition, post-deposition treatments, lattice mismatches, and interfacial morphology. The static piezo-voltage induced by the internal pressure across the CdS layer in a device may be rather significant reaching several tenths of a Volt. In addition to the recently reported effect of pressure perpendicular to the device surface [1], here we apply stress in lateral direction via bending the cells of two different configurations: on 3 mm glass superstrate and on flexible molybdenum (Mo) substrate. The observed reversible changes in major photovoltaic parameters are not small and can be related to the known strong piezoelectric effect in CdS. The effect of lateral stretching is found similar to that observed under pressure applied perpendicular to the film surface.