• Energy Research

In this study we analysed halide perovskite films deposited directly on crystalline silicon by means of two set-ups using different operating modes of the surface photovoltage (SPV) methods, i.e., the Kelvin probe force microscopy (KPFM) and the metal-insulator-semiconductor (MIS) technique. The KPFM allowed to visualize surface potential distribution on a microscale while MIS technique allowed to study SPV spectral dependence. We studied wavelength dependent SPV of these samples, which allowed us to effectively vary the probe depth in the sample and discern the contribution from each interface to the overall effect measured under white light illumination. Depending on where the photocarriers are generated, different SPV signals are observed: at the perovskite/Si interface, the signal depends on Si doping type, while at the surface the SPV is always negative indicating downward surface band bending. This is confirmed by analysing SPV phase measured in the AC MIS mode. In addition, distinction between slow and fast processes contributing to measured SPV was possible. It has been observed, that with decreasing the illumination wavelength, the processes causing SPV become slower, which can indicate that high energy photons not only generate electronic photocarriers but can also induce chemical changes with creation of defects or ionic species that also modify the measured SPV.

The properties of GaAsSbN and GaAsSb layers grown by liquid-phase epitaxy on n-GaAs substrates were investigated in a comparative plan with a view of their possible application in multi-junction solar cells. To avoid non-uniformity effects in the composition of these compounds with two or three different group-V volatile elements, the crystallization was carried out from finite melt with a thickness of 0.5 mm at low (<560 °C) temperatures. X-ray microanalysis and X-ray diffraction were used to determine the composition, lattice mismatch, and crystalline quality of the epitaxial layers. The morphology and surface roughness were examined by atomic force microscopy. Surface photovoltage (SPV) spectroscopy at room temperature was applied to study the optical absorption properties and the photocarrier transport in the samples. The long-wavelength photosensitivity of the GaAsSbN and GaAsSb layers, determined from their SPV spectra, is extended down to 1.2 eV. Although GaAsSb has a slightly larger lattice mismatch with the GaAs substrate compared to GaAsSbN, it presents a higher photoresponse, since, in GaAsSbN, the incorporation of N induces additional recombination centres. Therefore, GaAsSb could be an alternative to GaAsSbN for solar cell applications.