Researchers are investigating the bulk photovoltaic effect in a promising material for future solar energy harvesting technologies. The bulk photovoltaic effect (BPV) is a rare phenomenon that allows some materials to outperform traditional p-n junctions in solar cells. In a recent breakthrough, researchers from Japan have experimentally confirmed for the first time the effect of BPV on the alpha phase of indium selenide (α-In).₂look₃) along the out-of-plane direction, in agreement with previous theoretical predictions. Impressive conversion efficiencies achieved in α-In devices₂look_3, It is an important step forward for new generation solar cell and photosensor technologies.

A solid understanding of the photovoltaic effect, where light can be converted into useful electrical energy, is central to the design and development of solar cells. Most solar cells today use pn junctions, taking advantage of the photoelectric effect that occurs at the interface between different materials. However, such designs are limited by the Shockley-Queisser limit, which severely limits the theoretical maximum solar energy conversion efficiency and imposes a trade-off between voltage and current that can be produced by the photovoltaic effect.

Investigation of BPV effect in crystalline materials

However, some crystalline materials exhibit an intriguing phenomenon known as the bulk photovoltaic effect (BPV). In materials that do not have internal symmetry, electrons excited by light may move coherently in a particular direction rather than returning to their original position. This results in what are known as “cutting currents”, which leads to the BPV effect occurring. Although experts estimate that indium selenide is in the alpha phase (α-In₂look₃) is a possible candidate to demonstrate this phenomenon, but has not yet been investigated experimentally.

To fill this knowledge gap, a research team from Japan led by Associate Professor Noriyuki Urakami of Shinshu University decided to study the effect of BPV on α-In.₂look_3. Their findings were recently published in the journal Applied Physics Letters.

“This material has recently become a hot topic in condensed matter physics because it can produce a shear current. Our work is the first to demonstrate this prediction experimentally,” shares Professor Urakami.

Multilayer α-In2Se3 device

First, the researchers produced a multilayer device consisting of a thin layer of α-In.₂look_3, It is sandwiched between two layers of transparent graphite. These graphite layers served as electrodes and were connected to a voltage source and ammeter to measure the currents generated during light irradiation. The team specifically used this particular layer arrangement because they focused on out-of-plane shear currents in the direction of the α-In layer. ₂ look₃.

After testing with different external voltages and different frequencies of light, the researchers confirmed the above predictions by confirming the existence of bias currents in the out-of-plane direction. The BPV effect was observed over a wide range of light frequencies.

Most importantly, researchers evaluated the potential of the BPV effect on α-In.₂look₃ and compared this to the effect in other materials. “Our α-In device₂look₃ Professor Urakami noted that it exhibits a quantum efficiency several orders of magnitude higher than that of other ferroelectric materials and comparable to the efficiency of low-dimensional materials with enhanced electrical polarization. He further adds: “This discovery will guide material selection for the development of functional photovoltaic devices in the near future.”

The research team hopes their efforts will eventually have a positive impact on the environment by encouraging renewable energy production. “Our findings have the potential to further accelerate the deployment of solar cells, one of the fundamental technologies for harvesting energy from the environment and a promising route to a carbon-neutral society,” concludes hopeful Professor Urakami.

We hope that this work will lead to further research into improving the design of sensitive photodetectors as well as significantly increasing the performance of solar cells by exploiting the BVP effect.