Voltage loss in polymer solar cells down to the dielectric constant

by | Aug 6, 2014

High dielectric constant polymer solar cells found to behave as efficiently as their inorganic counterparts.

Compared to inorganic solar cells such as silicon, the cell voltage in organic solar cells is significant less than the voltage that would be expected, given the semiconductor bandgap energy. The open-circuit voltage in most polymer cells is less than half of the semiconducting polymer bandgap voltage, which is why the efficiency of polymer solar cells is still low compared to inorganic cells.

Now, using charge modulation electroabsorption spectroscopy, Chen and Tsang et al., from the University of Florida have demonstrated that this energy loss is due to the energy required to separate the charges. Because of the low dielectric constants in most polymers, this voltage loss can be as large as 0.35 V. On the other hand, they show that given the right polymer, with an appropriately high dielectric constant (close to 5), very little voltage loss is observed, and the polymer cell behaves like its inorganic counterpart. Choosing the right polymer, in other words, could have a major effect on the performance of your organic photovoltaics.