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 use of sodium tetrafluoroborate as the surface passivator of tin oxide electron‐transporting layer to improve the performance and stability of perovskite‐based solar cells is demonstrated. With NaBF4 treatment, defects on the SnO2 surface are alleviated, resulting in a considerably lower trap density at the SnO2 perovskite interfaces; consequently, the charge extraction properties are enhanced.
Abstract
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 time‐resolved photoluminescence results.
Posttreatment of titanium oxide (TiO2) 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 TiO2 and consequently accelerate the rutile phase transformation. X‐ray photoelectron spectroscopy results reveal the appearance of a Ti3+ 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 TiO2 layer. The Li‐treated TiO2 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 TiO2 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 time‐resolved photoluminescence results.
Photovoltaic materials are impacted by the photoinduced charge separation behavior, which can be further improved by modifying the underlying layer that the perovskite is prepared on top of. The impacts of using alkali salts on porous TiO2 from experimental and computational points of view are investigated to understand such surface passivation of a solar cell device.
Tin‐Oxide Perovskites
In article number 2200964, 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.
Photovoltaic Performance Stability
The most fundamental properties of photovoltaic materials are impacted by the photoinduced charge separation behavior, which can be improved by modifying the ...underlying layer that the perovskite is prepared on top. In article number 2201632, Non Thongprong, Nopporn Rujisamphan, and colleagues investigate the impacts of using alkali salts on porous TiO2 from experimental and computational points of view to provide a better understanding of such surface passivation.
