Demonstration of quantum solar cell concepts in InGaP barrier structures

Quantum solar cell structures seek to harness a wide spectrum of photons by embedding low energy-gap wells or dots within a high energy-gap matrix. Contrary to previous reports and expectations, we find that an extended region of narrow band-gap material can be inserted into the depletion region of a wide band-gap p-n junction without significantly degrading the dark diode characteristics. In particular, thin InGaP barrier layers are found to be extremely effective at reducing the diode dark current of GaAs-based diodes by several orders of magnitude. Our results imply a clear separation in the quasi-Fermi level at the InGaP/GaAs heterointerface, as well as efficient photogenerated carrier transport over the potential energy barrier. This novel GaAs-based device structure has produced over a 100 mV increase in the open circuit voltage without any degradation in the short circuit current.