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See detailCoevaporation Stabilizes Tin-Based Perovskites in a Single Sn-Oxidation State
Singh, Ajay UL; Hieulle, Jeremy UL; Ferreira Machado, Joana Andreia UL et al

in Nano Letters (2022)

Chemically processed methylammonium tin-triiodide (CH3NH3SnI3) films include Sn in different oxidation states, leading to poor stability and low power conversion efficiency of the resulting solar cells ... [more ▼]

Chemically processed methylammonium tin-triiodide (CH3NH3SnI3) films include Sn in different oxidation states, leading to poor stability and low power conversion efficiency of the resulting solar cells (PSCs). The development of absorbers with Sn [2+] only has been identified as one of the critical steps to develop all Sn-based devices. Here, we report on coevaporation of CH3NH3I and SnI2 to obtain absorbers with Sn being only in the preferred oxidation state [+2] as confirmed by X-ray photoelectron spectroscopy. The Sn [4+]-free absorbers exhibit smooth highly crystalline surfaces and photoluminescence measurements corroborating their excellent optoelectronic properties. The films show very good stability under heat and light. Photoluminescence quantum yields up to 4 × 10^-3 translate in a quasi Fermi-level splittings exceeding 850 meV under one sun equivalent conditions showing high promise in developing lead-free, high efficiency, and stable PSCs. [less ▲]

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See detailInhomogeneities in lead halide perovskite absorbers revealed by quantitative Photoluminescence Imaging
Phirke, Himanshu UL; Singh, Ajay UL; Hieulle, Jeremy UL et al

in Phirke, Himanshu; Singh, Ajay; Hieulle, Jeremy (Eds.) et al Inhomogeneities in lead halide perovskite absorbers revealed by quantitative Photoluminescence Imaging (2022, April 20)

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See detailImpact of metallic potassium post-deposition treatment on epitaxial Cu(In, Ga)Se2
Martin Lanzoni, Evandro UL; Ramirez Sanchez, Omar UL; Phirke, Himanshu UL et al

in Thin Solid Films (2021)

Alkali post-deposition treatments (PDTs) of Cu(In, Ga)Se2 (CIGSe) absorbers are known to improve the power conversion efficiency of the thin-film solar cell devices. The PDTs are usually carried out via ... [more ▼]

Alkali post-deposition treatments (PDTs) of Cu(In, Ga)Se2 (CIGSe) absorbers are known to improve the power conversion efficiency of the thin-film solar cell devices. The PDTs are usually carried out via evaporation of alkali fluorides in a selenium atmosphere onto a hot substrate. In this work, an alkali metal dispenser was used to evaporate pure metallic potassium onto epitaxial CIGSe absorbers. Subsequently, the absorber layers were heated in-situ to monitor chemical reactions and diffusion into the bulk. Due to the absence of grain boundaries, fluorine, and selenium, the effect of K on CIGSe absorber properties can be directly monitored. We find that potassium effectively diffuses into the bulk of epitaxial CIGSe absorber layers. The diffusion depends on the Cucontent of the CIGSe absorbers, in which Cu-depleted films present higher diffusion rates of K. Photoluminescence (PL) imaging corroborates that K in the bulk of the CIGSe absorber increases the PL yield, suggesting a passivation of defects or an increase in doping. This work highlights that alkali PDTs are not limited by interface and grain boundary modifications but also changes the absorber bulk properties, which needs to be taken into account. [less ▲]

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