Scientists from the Institute for Open and Trans­disciplinary Research Initiatives at Osaka University discovered a new feature of solar cells made from antimony sulfiodide:­sulfide composite they termed the wavelength-dependent photo­voltaic effect (WDPE). The team determined that changing the color of incident light from visible to ultra­violet induced a reversible change in the output voltage, while leaving the current generated unchanged. This work may lead to new func­tional light-sensing and imaging devices.

Recent progress in thin film PV devices has attracted much attention owing to their low-cost process, flexi­bility, and light weight. However, although various PV devices have been reported so far, reversible and fast wavelength-dependent responses have not been previously observed. To distinguish between irra­diation colors using a single photodiode, a liquid crystal filter must be used that can electroni­cally switch the absorption color range. However, these filters are bulky; being able to perform color detection without requiring such filters would be useful for minimizing the size of photo­voltaic devices.

Now, the team of researchers at Osaka University have built new photovoltaic devices made from antimony sulfiodide:­sulfide composite and found a novel effect. The voltage generated could be changed by switching the light color, in which ultra­violet reduced the output voltage. That is, a reversible change in the current versus voltage curves could be obtained simply by shining different colors of light on the device. “Such a dramatic shift in voltage is not observed in silicon, perovskites, or organic solar cells,” explains Ryosuke Nishikubo.

To better understand the mechanism behind this effect, the scientists then performed transient photo­voltage (TPV) and photo-induced charge extrac­tion by linearly increasing voltage (photo-CELIV). These experiments helped clarify the dramatic and reversible change in charge carrier lifetime induced by ultraviolet irra­diation. The team concluded that WDPE was caused by metastable trap states at the heterojunction interface, generated by high energy charges. These inter­facial energy traps significantly reduced output voltage, and as a result, light of certain energies could be distin­guished based on the voltage. This change could be enhanced by the presence of the vapor from a polar solvent. “While our work helps advance basic science by explaining this novel effect, the research also has many potential appli­cations, including as a vapor detector,” says Akinori Saeki.

The newly discovered pheno­menon may be applied to light sensing used in everything from mobile phones to cars, to security or horti­cultural systems. It can also be a part of imaging appli­cations in medical and other scientific pursuits, such as space satellites and micro­photography. In addition, it is also poten­tially desirable as a renewable energy source, because of its low toxicity and low production cost. (Source: Osaka U.)

Reference: R. Nishikubo et al.: Unprecedented Wavelength Dependence of an Antimony Chalcohalide Photovoltaic Device, Adv. Func. Mat., online 28 June 2022; DOI: 10.1002/adfm.202201577

Link: Dept. of Applied Chemistry, Graduate School of Engineering, Osaka University, Osaka, Japan