Characterization of the Interfacial Defect Layer in Chalcopyrite Solar Cells by Depth-Resolved Muon Spin Spectroscopy

As devices become smaller and more complex, the interfaces between adjacent materials become increasingly important and are often critical to device performance. An important research goal is to improve the interface between the absorber and the window layer by inserting buffer layers to adjust the transition. Depth-resolved studies are key for a fundamental understanding of the interface. In the present experiment, the interface between the chalcopyrite Cu(In,Ga)Se-2 absorber and various buffer layers are investigated using low-energy muon spin rotation (mu SR) spectroscopy. Depth resolution in the nm range is achieved by implanting the muons with different energies so that they stop at different depths in the sample. Near the interface, a region about 50 nm wide is detected where the lattice is more distorted than further inside the absorber. The distortion is attributed to the long-range strain field caused by defects. These measurements allow a quantification of the corresponding passivation effect of the buffer layer. Bath-deposited cadmium sulfide provides the best defect passivation in the near interface region, in contrast to the dry-deposited oxides, which have a much smaller effect. The experiment demonstrates the great potential of low energy mu SR spectroscopy for microscopic interfacial studies of multilayer systems.

Automated summary

As devices become smaller and more complex, the interfaces between materials become more important in determining device performance. In this study, low-energy muon spin rotation (mu SR) spectroscopy was used to investigate the interface between the chalcopyrite Cu(In,Ga)Se-2 absorber and various buffer layers. Depth resolution in the nm range was achieved by implanting the muons at different energies. The study revealed a region near the interface where the lattice was more distorted than within the absorber, attributed to a long-range strain field caused by defects. The measurements allowed quantification of the passivation effect of the buffer layers, with cadmium sulfide providing the best defect passivation in the near interface region. The experiment demonstrated the potential of low energy mu SR spectroscopy for studying interfaces in multilayer systems.