Enhancing the open-circuit voltage in narrow-bandgap CuInSe2 solar cells via local contact passivation with Al2O3

A fabrication technique using Al2O3-passivated local contacts was employed to produce narrow-bandgap CuInSe2 (CISe) photoabsorbers, which are well-suited as bottom cell materials in tandem devices. However, the performances of CISe cells with narrow bandgaps are impeded by the recombination of charge carriers, which reduces the open-circuit voltage (VOC). To overcome this limitation, an additional Al2O3 passivation layer was added to CISe solar cells. This enhanced the VOC while maintaining a spectral response of up to 1.0 eV, thereby boosting the photovoltaic conversion efficiency of the devices. Further, the Al2O3 passivation layer within the CISe absorber effectively mitigated the recombination of charge carriers, resulting in a substantial improvement in efficiency. Specifically, the Al2O3-passivated local contact hindered the charge-carrier recombination at the rear contact, leading to a marked increase in the VOC. Consequently, the overall photovoltaic conversion efficiency increased significantly from 10.4 % to 13 %. These results are expected to greatly further the development of CISe solar cells and achieve remarkable photovoltaic conversion efficiencies.