Researchers have explored the bulk photovoltaic effect in a promising material for next-generation solar harvesting technologies.
The bulk photovoltaic (BPV) effect is an uncommon phenomenon that may enable certain materials to outperform the conventional p–n junctions used in solar cells.
In a new study, researchers from Japan have experimentally demonstrated the BPV effect in alpha-phase indium selenide (α-In2Se3) for the first time along the out-of-plane direction, validating previous theoretical predictions.
The remarkable conversion efficiency recorded in their α-In2Se3 device signals a promising advancement for future solar cell technologies and photosensors.
Understanding the bulk photovoltaic effect in solar cells
A firm understanding of the photovoltaic effect, by which light can be converted into useful electrical energy, lies at the core of solar design and development.
Today, most solar cells employ p–n junctions, leveraging the photovoltaic effect at different materials’ interfaces.
However, these designs are constrained by the Shockley–Queisser limit, which hard-caps their theoretical maximum solar conversion efficiency and imposes a trade-off between the voltage and current that can be produced via the photovoltaic effect.
Despite this, certain crystalline materials exhibit an intriguing phenomenon known as the bulk photovoltaic (BPV) effect. In materials lacking internal symmetry, electrons excited by light can move coherently in a specific direction instead of returning to their original positions.
This results in what are known as ‘shift currents,’ which generate the BPV effect.
Although experts have predicted that alpha-phase indium selenide could demonstrate this phenomenon, it hasn’t yet been experimentally investigated.
Exploring the BPV effect on alpha-phase indium selenide
First, the researchers produced a layered device comprising a thin α-In2Se3 layer sandwiched between two transparent graphite layers.
These graphite layers were electrodes and connected to a voltage source and an ammeter to measure any generated currents upon light irradiation.
Notably, the team employed this specific arrangement of layers because they focused on the shift currents occurring in the out-of-plane direction in the α-In2Se3 layer.
After testing with different external voltages and incident light of various frequencies, the researchers verified the existence of shift currents in the out-of-plane direction, confirming the abovementioned predictions. The BPV effect occurred throughout a wide range of light frequencies.
Most importantly, the researchers gauged the potential of the BPV effect in α-In2Se3 and compared it to that in other materials.
“Our α-In2Se3 device demonstrated a quantum efficiency several orders of magnitude higher than other ferroelectric materials and a comparable one to that of low-dimensional materials with enhanced electric polarisation,” explained Professor Noriyuki Urakami, who led the research.
Future environmental impact of the research
The research team is hopeful that their efforts will eventually have a positive environmental impact by contributing to the field of renewable energy generation.
This discovery will guide material selection for the development of functional photovoltaic devices in the near future.
Professor Urakami concluded: “Our findings have the potential to further accelerate the spread of solar cells, one of the key technologies for environmental energy harvesting and a promising avenue towards a carbon-neutral society.”
