Photovoltaic devices made from the antimony sulfiodide:sulfide composite. Photo: Ryosuke Nishikubo.
Photovoltaic devices made from the antimony sulfiodide:sulfide composite. Photo: Ryosuke Nishikubo.

Researchers from the Institute for Open and Transdisciplinary Research Initiatives at Osaka University in Japan have discovered a new feature of solar cells made from an antimony sulfiodide:sulfide composite, which they term the wavelength-dependent photovoltaic effect (WDPE).

The researchers found that changing the color of incident light from visible to ultraviolet induced a reversible change in the output voltage of solar cells made from the composite, while leaving the current generated unchanged. This work, which is reported in a paper in Advanced Functional Materials, may lead to new functional light-sensing and imaging devices.

Photovoltaic (PV) devices – such as solar cells and photodiodes –convert light energy into electronic power, and are important as renewable energy sources and light/image sensors. Recent progress in thin film PV devices has attracted much attention, due to their low cost, flexibility and light weight.

Although many PV devices have been reported so far, reversible and fast wavelength-dependent responses have not previously been observed. To distinguish between different color light using a single photodiode, a liquid crystal filter must be used that can electronically switch the absorption color range, but these filters are bulky. Being able to perform color detection without requiring such filters would be useful for minimizing the size of PV devices.

Now, a team of researchers at Osaka University has built new photovoltaic devices made from an antimony sulfiodide:sulfide composite and found a novel effect. The voltage generated can be changed by switching the color of the light, with ultraviolet light reducing the output voltage. In other words, a reversible change in the current versus voltage curves can be obtained simply by shining light of different colors on the device.

“Such a dramatic shift in voltage is not observed in silicon, perovskites or organic solar cells,” says first author Ryosuke Nishikubo.

To better understand the mechanism behind this effect, the researchers 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 exposure to ultraviolet radiation.

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, allowing light of certain energies to be distinguished based on the voltage. This change could be enhanced by the presence of 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 senior author Akinori Saeki.

The newly discovered phenomenon could be applied to light sensing in everything from mobile phones to cars to security to horticultural systems. It could also form part of imaging applications in medical and other scientific pursuits, such as space satellites and microphotography. In addition, the composite solar cell is potentially desirable as a renewable energy source, because of its low toxicity and low production cost.

This story is adapted from material from Osaka University, with editorial changes made by Materials Today. The views expressed in this article do not necessarily represent those of Elsevier. Link to original source.