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Abstract In this paper, we use Polyethylene Oxide (PEO) particles to control the morphology of Formamidinium (FA)-rich perovskite films and achieve large grains with improved optoelectronic properties. Consequently, a planar perovskite solar cell (PSC) is fabricated with additions of 5 wt% of PEO, and the highest PCE of 18.03% was obtained. This solar cell is also shown to retain up to 80% of its initial PCE after about 140 h of storage under the ambient conditions (average relative humidity of 62.5 ± 3.25%) in an unencapsulated state. Furthermore, the steady-state PCE of the PEO-modified PSC device remained stable for long (over 2500 s) under continuous illumination. This addition of PEO particles is shown to enable the tuning of the optoelectronic properties of perovskite films, improvements in the overall photophysical properties of PSCs, and an increase in resistance to the degradation of PSCs. 

We use transient optical absorption and time-resolved terahertz THz spectroscopy to investigate photoexcitations in Ti₃C₂, Mo₂Ti₂C₃, and Nb₂C. Measurements reveal pronounced plasmonic effects. Monitoring them provides insights into thermal relaxation processes and low thermal conductivity. 

CuBiW 2 O 8 (CBTO), with a band gap of 1.9–2.0 eV, responds to a wide region of the electromagnetic spectrum, which makes it a good candidate for solar-driven photocatalytic energy conversion and water treatment. We have previously demonstrated a Cu-rich solid state approach that enables the synthesis of CBTO accompanied by thermodynamically stable Bi 2 WO 6 impurity. Here, we describe an improved synthesis protocol with decreased impurity and synthesis time, and the first demonstration of CBTO as a functional material using photocatalytic Cr( vi ) photoreduction as a probe reaction. Transient absorption spectroscopy (TAS) was performed to investigate the ultrafast dynamics of the charge carriers after photoexcitation. The presence of two populations of photoexcited carriers was found, including short-lived free carriers with ∼10 ps lifetime and long-lived shallowly-trapped carriers with ∼1 ns lifetime. Together with carrier mobilities measured in our previous study, the new TAS results indicate that the long-lived charges have diffusion lengths similar to the CBTO particle size and were likely responsible for the majority of the photocatalytic activity. High activity of CBTO for Cr( vi ) photoreduction (∼100% reduction of 5 mg L −1 of Cr( vi ) in 15 minutes) was demonstrated, which clearly establishes the promise of this novel oxide for visible light-driven photocatalytic applications. Radical quenching experiments indicate that both ˙OH radicals and O 2 ˙ − radicals are produced by CBTO and are involved in the photoreduction of Cr( vi ). Repeated photocatalysis tests and analysis of the surface after the reaction show that CBTO is a stable and potentially reusable catalyst. Insights gained from correlating the synthesis conditions, carrier dynamics, and reactive species suggests that CBTO prepared with the improved protocol would be a favorable choice for photocatalytic reactions such as water decontamination from organic pollutants, water splitting, and solar fuel generation using visible light.