Passivating Surface Defects and Reducing Interface Recombination in CuInS₂ Solar Cells by a Facile Solution Treatment

Abstract

Interface recombination at the absorber surface impedes the efficiency of a solar cell with an otherwise excellent absorber. The internal voltage or quasi‐Fermi‐level splitting (qFLs) measures the quality of the absorber. Interface recombination reduces the open‐circuit voltage (VOC) with respect to the qFLs. A facile solution‐based sulfur postdeposition treatment (S‐PDT) is explored to passivate the interface of CuInS2 grown under Cu‐rich conditions, which show excellent qFLs values, but much lower VOCs. The absorbers are treated in S‐containing solutions at 80 °C. Absolute calibrated photoluminescence and current–voltage measurements demonstrate a reduction of the deficit between qFLs and VOC by almost one‐third compared with the untreated device. Temperature dependence of the open‐circuit voltage shows increased activation energy for the dominant recombination path, indicating less interface recombination. In addition, capacitance transients reveal the presence of slow metastable defects in the untreated solar cell. The slow response is considerably reduced by the S‐PDT, suggesting passivation of these slow metastable defects. The results demonstrate the effectiveness of solution‐based S‐treatment in passivating defects, presenting a promising strategy to explore and reduce defect states near the interface of chalcogenide semiconductors.

Origin of Interface Limitation in Zn(O,S)/CuInS2-Based Solar Cells

“…32 For the Cu-rich CuInS 2 -based device, the value of E a is significantly lower than the bulk band gap (E g ) of CuInS 2 (of 1.51 eV obtained by d(EQE)/dE analysis, see Figure S1), in agreement with earlier works. 5,31,33 For the Cupoor CuInS 2 device, E a agrees (within the experimental uncertainty) with E g . However, the confidence in E a is rather low as the device exhibits distortions in its I−V behavior at lower temperatures in an "S shape" (see Figure S2b), which is also the reason why the Cu-poor device has a rather poor FF.…”

GaAs/GaInP nanowire solar cell on Si with state-of-the-art Voc and quasi-Fermi level splitting

“…This has been observed in other types of solar cells, e.g. CIS, 67 CIGS 68,69 or perovskites. 70 In our case, the efficient extraction of the majority charge carriers may be prevented by the p-Si/p-GaP/p-GaAs heterointerface at the foot and by the i-GaAs/n-GaInP/ITO heterointerface at the top, and they may recombine at the dislocations near the i-GaAs/n-GaInP interface introduced due to GaInP shell composition variation along the NW axis.…”

Near surface defects: Cause of deficit between internal and external open‐circuit voltage in solar cells

“…VOC,in -VOC,ex. The deficit can be observed in thin film solar cells such as Cu(In,Ga)(Se,S)2, 5,6 CdTe, 7 perovskite, 4,8,9 and is associated to interface recombination in the device. 4,[9][10][11][12][13] Identifying the source of interface recombination and the underlying qFLs gradient is crucial for achieving higher efficiency in these devices and enabling better understanding of device physics.…”