Observation of Space Charge Dynamics Inside an All Oxide Based Solar Cell

Abstract

The charge transfer dynamics at interfaces are fundamental to know the mechanism of photovoltaic processes. The internal potential in solar cell devices depends on the basic processes of photovoltaic effect such as charge carrier generation, separation, transport, recombination, etc. Here we report the direct observation of the surface potential depth profile over the cross-section of the ZnO nanorods/Cu2O based solar cell for two different layer thicknesses at different wavelengths of light using Kelvin probe force microscopy. The topography and phase images across the cross-section of the solar cell are also observed, where the interfaces are well-defined on the nanoscale. The potential profiling results demonstrate that under white light illumination, the photoinduced electrons in Cu2O inject into ZnO due to the interfacial electric field, which results in the large difference in surface potential between two active layers. However, under a single wavelength illumination, the charge carrier generation, separation, and transport processes between two active layers are limited, which affect the surface potential images and corresponding potential depth profile. Because of changes in the active layer thicknesses, small variations have been observed in the charge carrier transport mechanism inside the device. These results provide the clear idea about the charge carrier distribution inside the solar cell in different conditions and show the perfect illumination condition for large carrier transport in a high performance solar cell.

Imaging the Anomalous Charge Distribution Inside CsPbBr3 Perovskite Quantum Dots Sensitized Solar Cells

“…However, Kelvin probe force microscopy (KPFM), a modified version of atomic force microscopy (AFM), is a noncontact surface technique used to measure the local contact potential difference (CPD) between a conducting AFM tip and the sample. − The spatial resolution of this microscopy is higher than the other techniques, such as EBIC and PES, and it allows simultaneous imaging of the topography and surface potential with nanoscale resolution . In recent times, KPFM has been employed to observe the surface potential distribution across the layers of solar cell devices like inorganic, organic heterojunction, and bulk perovskite sensitized solar cells. − …”

Enhanced UV Flexible Photodetectors and Photocatalysts Based on TiO2 Nanoplatforms

“…The KPFM experiments were carried out in a double pass mode, and the second pass was performed at an optimized height of 50 nm above the topographic trace [37]. During UV irradiation, the materials were illuminated with UV (λ = 365 nm) [38] collimated LEDs from Thorlabs. The root mean square (RMS) roughness of each substrate was obtained from atomic force microscopy (AFM) topography images.…”

Polarization Effects in Graded AlGaN Nanolayers Revealed by Current-Sensing and Kelvin Probe Microscopy

“…In this regard, an in-depth study of polarization-induced effects resulting from changes in both the spontaneous and piezoelectric polarizations in graded Al x Ga 1– x N layers in comparison to local electrical properties is currently relevant. Kelvin probe force microscopy (KPFM) and conductive atomic force microscopy (C-AFM) have recently shown to be effective in the characterization of semiconductor electrical parameters at the nanoscale. − Here, we can use these unique techniques to measure cross sections of a specially grown composite structure that consists of different groups of graded Al x Ga 1– x N layers separated by GaN spacers. This approach allows to compare polarization-doped materials with different parameters and avoid possible errors related to different background doping levels and the surface properties resulting from separate samples.…”