This open access document is posted as a preprint in the Beilstein Archives at https://doi.org/10.3762/bxiv.2021.2.v1 and is considered to be an early communication for feedback before peer review. Before citing this document, please check if a final, peer-reviewed version has been published. This document is not formatted, has not undergone copyediting or typesetting, and may contain errors, unsubstantiated scientific claims or preliminary data.

In this work, we use pump-probe Kelvin Probe Force Microscopy (pp-KPFM) in combination with non-contact atomic force microscopy (nc-AFM) under ultrahigh vacuum, to investigate the nature of the light-induced surface potential dynamics in alumina-passivated crystalline silicon, and in an organic bulk heterojunction thin film based on the PTB7-PC71BM tandem. In both cases, we demonstrate that it is possible to identify and separate the contributions of two different kinds of photo-induced charge distributions that give rise to potential shifts with opposite polarities, each characterized by different dynamics. The data acquired on the passivated crystalline silicon are shown to be fully consistent with the band-bending at the silicon-oxide interface, and with electron trapping processes in acceptors states and in the passivation layer. The full sequence of events that follow the electron-hole generation can be observed on the pp-KPFM curves, i.e. the carriers spatial separation and hole accumulation in the space charge area, the electron trapping, the electron-hole recombination, and finally the electron trap-release. Two dimensional dynamical maps of the organic blend photo-response are obtained by recording the pump-probe KPFM curves in data cube mode, and by implementing a specific batch processing protocol. Sample areas displaying an extra positive SPV component characterized by decay time-constants of a few tens of microseconds are thus revealed, and are tentatively attributed to specific interfaces formed between a polymer-enriched skin layer and recessed acceptor aggregates. Decay time constant images of the negative SPV component confirm that the acceptor clusters act as electron-trapping centres. Whatever the photovoltaic technology, our results exemplify how some of the SPV components may remain completely hidden to conventional SPV imaging by KPFM, with possible consequences in terms of photo-response misinterpretation. This work furthermore highlight the need of implementing time-resolved techniques that can provide a quantitative measurement of the time-resolved potential.

We report a correlative analysis between corona oxide characterization of semiconductor (COCOS) and Kelvin probe force microscopy (KPFM) for the study of embedded silicon-oxide interfaces in the field of chemical and field-effect passivation. Analyzed parameters by these measurements are linked to different factors and specifically to defects density of embedded silicon-dielectric interfaces, surface band bending or the distribution of charges in the nearest surface volume. Furthermore, this COCOS-KPFM correlative analysis turns out to be a useful method to access to chemical and field-effect passivation. We confirm that it is possible to differentiate the influence of local band bending on sample passivation (i.e. field effect passivation) from the effects due to the local recombination rates (i.e. chemical passivation). The measurements were carried on five different passivation layers, precisely, 10.5 nm-thick SiO2, 50 nm-thick SiN, 7nm-thick Al2O3, 7 nm-thick HfO2 and double layer of 7 nm-thick Al2O3 below 53 nm-thick Ta2O5. This correlative analysis indicates that HfO2 present to be the best chemical passivation and SiN is the worst case in term of field effect passivation for p-type silicon. Additionally, we confirm that Ta2O5 layer on top of Al2O3 increase the defects density.

This paper presents the characterization of alumina passivation layers using second harmonic generation (SHG). Based on nonlinear optics, the technique has the advantage of being rapid and non-destructive, especially for thin oxide layers. For the materials under study, the SHG is sensitive to the electronic and structural properties of the interface, particularly to the interfacial electric field (Edc), and thus allowing to characterize fixed oxide charges (Qox) in the oxide and interface traps density (Dit). Time-dependent SHG (TD-SHG) is firstly used here to probe samples with various Dit and a total oxide charges (Qtot), previously extracted using corona oxide characterization of semiconductor (COCOS). The measurement conditions are adjusted to focus on the impact of the fixed charges on the SHG signal. A more detailed analysis of the SHG versus input polarization is conducted in both experiments and simulations and it shows coherent evolution tendencies with the oxide charge.