Seeing photovoltaic devices in a new light

Figure 1

image: Photo of SbSI and SbSI:Sb2s3 photovoltaic devices.
vision Lake

Credit: Ryosuke Nishikubo

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

Photovoltaic (PV) devices – such as solar cells and photodiodes – that convert light energy into electronic power are important as renewable energy sources or as light/image sensors. Recent advances in thin film PV devices have attracted much attention due to their low-cost process, flexibility and light weight. Although several PV devices have been reported to date, reversible and fast wavelength-dependent responses have not been observed before. To distinguish between irradiation colors using a single photodiode, a liquid crystal filter that can electronically switch the absorption color range must be used. However, these filters are bulky; being able to perform color detection without the need for such filters would be helpful in minimizing the size of photovoltaic devices.

Now, a team of researchers from Osaka University has built new photovoltaic devices made of antimony sulfiodide:sulfide composite and found a new effect. The generated voltage could be changed by changing the light color, with ultraviolet lowering the output voltage. That is, a reversible change in the current versus voltage curves can be obtained by simply 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 first author Ryosuke Nishikubo.

To better understand the mechanism behind this effect, the scientists next performed transient photovoltage (TPV) and photoinduced charge extraction by increasing the voltage linearly (photo-CELIV). These experiments helped elucidate the dramatic and reversible change in charge carrier life caused 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 the 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 of a polar solvent. “While our work advances basic science by explaining this new effect, the research also has many potential applications, including as a vapor detector,” said senior author Akinori Saeki.

The newly discovered phenomenon can be applied to light detection used in everything from cell phones to cars, to security or horticultural systems. It can also be part of imaging applications in medical and other scientific activities, such as space satellites and microphotography. In addition, it is also potentially desirable as a renewable energy source, due to its low toxicity and low production costs.

The article, “Unprecedented Wavelength Dependency of an Antimony Chalcohalide Photovoltaic Device”, was published in Advanced functional materials at DOI:

About Osaka University

Osaka University was founded in 1931 as one of Japan’s seven Imperial Universities and is now one of Japan’s leading comprehensive universities with a broad disciplinary spectrum. This strength is accompanied by a unique drive for innovation that spans the entire scientific process, from basic research to the creation of applied technology with positive economic effects. Its commitment to innovation has been recognized in Japan and around the world and was named Japan’s most innovative university in 2015 (Reuters 2015 Top 100) and one of the most innovative institutions in the world in 2017 (Innovative Universities and the Nature Index Innovation 2017). Now Osaka University is taking advantage of its role as Designated National University Corporation selected by the Ministry of Education, Culture, Sports, Science and Technology to contribute to innovation for human well-being, sustainable development of society and social transformation.


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