InAs quantum dots based solar cell: Multi-excitons

A stack of 10 InAs quantum dot layers has been incorporated into an InxGa1-xAs(p doped)/InAs/InxGa1-xAs(n doped) heterojunction semiconductor device using molecular beam epitaxy. Atomic force microscopy revealed quantum dots of sizes 20 to 50 nm and heights of 2 to 5 nm. The density was 2x10¹⁰ quantum dots per cm² per layer. This device, when compared to InxGa1-xAs (p doped)/InxGa1-xAs(n doped) homojunction device with no InAs quantum dot layers, showed a 20 fold increase in the photocurrent density under 50 W lamp illumination however the open circuit voltage dropped. Exponential increase in the photocurrent might have been an effect of multiple exciton generation (carrier multiplication) due to discrete electronic wave functions in the nanometer sized InAs quantum dots.