Researchers discover a voltage that depends on the wavelength of incident light

Scientists at the Institute for Open and Transdisciplinary Research Initiatives at Osaka University discovered a new property of solar cells made from antimony sulfiodide:sulfide composite, which 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 light energy in electronic power are important as: renewable energysources 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 organics solar panels’ explains lead 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 cost. Significantly reduced these interfacial energy traps output voltageand as a result, light of certain energies could be distinguished on the basis of the Tension† 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.

Their research has been published in Advanced functional materials†