Surface photovoltage characterisation of metal halide perovskite on crystalline silicon using Kelvin probe force microscopy and metal-insulator-semiconductor configuration

Abstract

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.

Surface Photovoltage Study of Metal Halide Perovskites Deposited Directly on Crystalline Silicon

“…With further increasing hν, the absorption is more and more concentrated near the PVK surface. KPFM transients under 488 nm (2.54 eV) excitation have shown a downward energy band bending at the surface 18 (see also below), which agree with other reports. 2 The downward band bending induces a second component of the SPV signal with a phase in the II nd quadrant (negative SPV, phase between 90 and 180°).…”

“…For detection of the cantilever deflection, a laser diode emitting at 1310 nm is used, thus avoiding unwanted band-to-band light excitation of any of the sample components. 18 The contact potential difference (CPD) between the tip and the sample was measured scanning over an area of 2 × 2 μm 2 and the results were averaged for each horizontal line. CPD transients were recorded over time scales of minutes after switching on and off the illumination from three laser diodes with wavelengths of 980, 785, and 488 nm, respectively, and a photon flux density of approximately 5 × 10 17 cm −2 s −1 .…”

“…The SPV was then obtained by subtracting the CPD measured in the dark from the one measured under illumination. 18 A schematic of the sample during SPV measurements with the KPFM setup is shown in Figure 2.…”

“…The film thickness was between 400 and 500 nm. X-ray diffraction measurements revealed the highly crystalline nature of the PVK films exhibiting the dominant PVK phase and small amounts of a foreign phase originating from PbI 2 …”

“…KPFM measurements were performed in ambient conditions by a HORIBA/AIST-NT (TRIOS platform) scanning probe microscopy system using a conductive Pt/Ir AFM tip. For detection of the cantilever deflection, a laser diode emitting at 1310 nm is used, thus avoiding unwanted band-to-band light excitation of any of the sample components . The contact potential difference (CPD) between the tip and the sample was measured scanning over an area of 2 × 2 μm 2 and the results were averaged for each horizontal line.…”