Control of valence band offset of Cu(In, Ga)Se2 solar cells with single-graded band profile

We have revealed that the insertion of a Cu(In, Ga)(3)Se-5 layer at the CdS/Cu(In, Ga)Se-2 interface is effective for improving the efficiency of Cu(In, Ga)Se-2 solar cells fabricated at low temperatures and with single-graded band profiles. Although the double-graded profile is usually adopted for Cu(In, Ga)Se-2 solar cells grown at around 600 degrees C, the single-graded profile is more suitable for low-temperature-grown solar cells owing to the higher controllability of band profiling. We also analyzed the role of the Cu(In, Ga)(3)Se-5 layer by transmission electron microscopy energy-dispersive X-ray spectrometry (TEM-EDX) and scanning electron microscopy electron-beam-induced current (SEM-EBIC), and found that Cd diffuses to the Cu(In, Ga)(3)Se-5 layer, resulting in a shift of the pn-junction electrical interface from the highly defective structural interface. Finally, by applying this new band profile, VOC and FF increased, resulting in an efficiency improvement from 13.4 to 14.5% at a substrate temperature of 450 degrees C. (C) 2017 The Japan Society of Applied Physics