Passivating electron‐transporting layers (ETLs) with alkali salts have demonstrated a facial approach that is essential in healing defective surfaces, consequently improving the functionality and stability of perovskite‐based solar cells (PSCs). Herein, the pseudohalide salt of sodium tetrafluoroborate, whose anions have a higher electronegativity than other halide salts (i.e., iodide and chloride), with the potential to passivate the surface of tin oxide while enhancing the optoelectronic properties of a perovskite film, is presented. Meanwhile, the density functional theory calculations show that BF4−/F− ions exhibit a robust ionic interaction with an uncoordinated Sn4+ site. In contrast, the Na ion is bound to an oxygen atom of the OH− group, which helps reduce surface defect states and improves charge transfer properties. Thus, the best PSC exhibits a current density of 23.51 mA cm−2, an open‐circuit voltage of 1.10 V, and an excellent fill factor of 80.48, providing an efficiency of 20.82%, which exceeds that of a control device (18.38%). Importantly, the retention of the power conversion efficiency on NaBF4‐based PSCs without encapsulation is 18.44% after 1000 h of aging under ambient conditions, whereas the retention of a control device is only 16.08%.
The most fundamental properties of a photovoltaic material are its photoinduced charge generation and charge separation behavior, which are related to the spectral absorption properties of the material. For instance, upon illumination by one sun (AM1.5G), microcrystalline silicon (Si)-, gallium arsenide (GaAs)-, and gallium indium phosphide (GaInP)-based solar cells exhibit the following current densities: 29.72 mA cm À2 (for Si), 23.20 mA cm À2 (for GaAs), and 16.63 mA cm À2 (for GaInP). [1] These relative current densities are largely in line with their spectral absorption properties. Recently, organicinorganic metal halide perovskite solar cells (PSCs) have become the best candidates for photovoltaic (PV) applications, where rapid development in power conversion efficiencies (PCEs) of up to 25.2% for a single junction and 28.2% for a tandem configuration of silicon-based devices has recently been achieved. [2][3][4][5] Even though efficiencies have been An understanding of the spectrum-property relationship of perovskite solar cells when illuminated by light-emitting diodes that are used for indoor applications is necessary. Herein, it is aimed to explore the influences of correlated-color temperatures on a MAPbI 3 -based device under low-light conditions. Given an irradiance of approximately 3 W m À2 (or %1000 lx), a maximum free carrier generation rate of 1.0 Â 10 21 m À3 s À1 was found. Additionally, power conversion efficiencies (PCEs) up to 31.97%, 30.36%, and 28.98% with maximum power outputs of 13.66, 13.02, and 16.09 μW could be reached at 3000, 4000, and 6500 K, respectively. Additional increases in the PCEs were observed when highenergy blue light (in a range of 400-550 nm) was excluded during the currentvoltage sweeps. In combination with the surface photovoltage measurements, intense blue light (under 6500 K) had a minimal influence on the photoinduced charge separation signals when compared to those caused by 3000 and 4000 K light. As a solar cell, the PCE reached as high as 34.52%, which corresponded to 73.08% of the thermodynamic limit of its bandgap at 3000 K.
Posttreatment of titanium oxide (TiO 2 ) using lithium (Li) and cobalt (Co) precursors is widely adopted to modify the charge quenching property in perovskite solar cells (PSCs); however, the fundamental understanding of the effect of the modification layer on the material itself and, consequently, the photovoltaic performance stability is not complete. In this work, in situ X-ray diffraction measurements show that the Li and Co ions can diffuse into TiO 2 and consequently accelerate the rutile phase transformation. X-ray photoelectron spectroscopy results reveal the appearance of a Ti 3+ feature in both the Li-and Co-treated samples, suggesting that the treatment ions are partially located at the subsurface/surface of the spin-cast TiO 2 layer. The Li-treated TiO 2 exhibits greatly upshifted conduction band edges, which benefits charge extraction properties and improves the average device parameters in a complete PSC. To complement the experiments, density functional theory calculations are performed. While Li treatment initially results in enhanced electronic properties, Li-treated TiO 2 tends to have more surface vacancies over time and is more susceptible to adsorption and accumulation of iodide ions compared to the Co-treated sample, which is experimentally supported by surface photovoltage spectroscopy and timeresolved photoluminescence results.
Tin‐Oxide Perovskites
In article number http://doi.wiley.com/10.1002/solr.202200964, Non Thongprong, Thidarat Supasai, Nopporn Rujisamphan, and co‐workers presented the pseudohalide salt of sodium tetrafluoroborate, whose anions have a higher electronegativity than other halide salts, with the potential to passivate the surface of tin oxide while enhancing the optoelectronic properties of a perovskite film. The current study presents a facile and effective method for enhancing the moderate thermal stability and performance of solar cell devices.
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