Extreme voltage recovery in GaAs:Ti intermediate band solar cells

Intermediate band materials incorporate a collection of energy levels with special optoelectronic properties within the semiconductor bandgap. This feature broadens the energy range of the solar spectrum useful for photovoltaic conversion and has the potential for enabling both high-current and high-voltage photovoltaic cells. Here we present our preliminary results on a novel intermediate band solar cell based on creating an intermediate band through the incorporation of a large concentration of Ti atoms in a GaAs crystal. The characterization of the material verifies a high concentration of incorporated Ti and the absence of structural defects. The cells show below-bandgap photon absorption with a likely contribution from As antisites and Ga vacancies. The initially degraded open-circuit voltage of the cells exhibits a high voltage recovery from 0.1 V (at room temperature and one-sun irradiance conditions) to 1.4 V (at low temperature and concentrated light).

► A new type of IB material is conceived by incorporating large amounts of Ti atoms in GaAs.
► A GaAs:Ti IBSC and its corresponding GaAs control solar cell are designed and fabricated.
► SIMS and TEM verify the incorporation of Ti and the absence of structural defects.
► Opto-electrical characterization (QE and PR) reveals sub-bandgap photoresponse.
► The “voltage preservation” principle is verified by low-temperature-concentrated-light I-V.