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   The impact of Kelvin probe force microscopy operation modes and environment on grain boundary band bending in perovskite and Cu(In,Ga)Se2 solar cellsMartin Lanzoni, Evandro  ; Gallet, Thibaut ; Spindler, Conrad et alin Nano Energy (2021), 88 An in-depth understanding of the electronic properties of grain boundaries (GBs) in polycrystalline semiconductor absorbers is of high importance since their charge carrier recombination rates may be very ... [more ▼] An in-depth understanding of the electronic properties of grain boundaries (GBs) in polycrystalline semiconductor absorbers is of high importance since their charge carrier recombination rates may be very high and hence limit the solar cell device performance. Kelvin Probe Force Microscopy (KPFM) is the method of choice to investigate GB band bending on the nanometer scale and thereby helps to develop passivation strategies. Here, it is shown that the workfunction, measured with amplitude modulation (AM)-KPFM, which is by far the most common KPFM measurement mode, is prone to exhibit measurement artifacts at grain boundaries on typical solar cell absorbers such as Cu(In,Ga)Se2 and CH3NH3PbI3. This is a direct consequence of a change in the cantilever–sample distance that varies on rough samples. Furthermore, we critically discuss the impact of different environments (air versus vacuum) and show that air exposure alters the GB and facet contrast, which leads to erroneous interpretations of the GB physics. Frequency modulation (FM)-KPFM measurements on non-air-exposed CIGSe and perovskite absorbers show that the amount of band bending measured at the GB is negligible and that the electronic landscape of the semiconductor surface is dominated by facet-related contrast due to the polycrystalline nature of the absorbers. [less ▲] Detailed reference viewed: 39 (2 UL)Electronic and compositional properties of the rear-side of stoichiometric CuInSe2 absorbersKameni Boumenou, Christian ; ; et alin Progress in Photovoltaics (2020) In-depth understanding and subsequent optimization of the contact layers in thin film solar cells are of high importance in order to reduce the amount of nonradiative recombination and thereby improve ... [more ▼] In-depth understanding and subsequent optimization of the contact layers in thin film solar cells are of high importance in order to reduce the amount of nonradiative recombination and thereby improve device performance. In this work, the buried MoSe2/CuInSe2 interface of stoichiometric absorbers is investigated with scanning tunneling spectroscopy and Kelvin probe force microscopy combined with compositional measurements acquired via photo-electron spectroscopy after a mechanical lift-off process. We find that the local density of states, as measured with scanning tunneling spectroscopy, is similar to the front-side of ultra-high vacuum annealed CISe absorbers. The grain boundaries exhibit a weak upward band bending, opposite to Cu-poor CuGaSe2, and we measure an increased Cu accumulation at the rear CISe surface compared to the bulk composition and a non-zero concentration of Cu on the Mo-side. Grazing incidence X-ray diffraction measurements corroborate that a small amount of a CuxSe secondary phase is present at the MoSe2/CuInSe2 interface in contrast to reports on Cu-poor material. Our findings shed new light into the complex interface formation of CuInSe2-based thin film solar cells grown under Cu-rich conditions. [less ▲] Detailed reference viewed: 53 (9 UL)Passivation of the CuInSe2 surface via cadmium pre-electrolyte treatmentKameni Boumenou, Christian ; ; et alin Physical Review Materials (2020) Detailed reference viewed: 179 (16 UL) |
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