Current solar cells are able to convert into electricity around 20% of the energy received from the Sun, but a new technique has the potential to convert around 60% of it by funneling the energy more efficiently.
UK researchers can now ‘funnel’ electrical charge onto a chip. Using the atomically thin semiconductor hafnium disulphide (HfS2), which is oxidized with a high-intensity UV laser, the team were able to engineer an electric field that funnels electrical charges to a specific area of the chip, where they can be more easily extracted.
This method has the potential to harvest three times the energy compared with traditional systems. The researchers believe their breakthrough could result in solar panels, no bigger than a book, producing enough energy to power a family-sized house.
Previously the group created the best transparent conducting material.
Abstract – Strain-engineered inverse charge-funnelling in layered semiconductors
The control of charges in a circuit due to an external electric field is ubiquitous to the exchange, storage and manipulation of information in a wide range of applications. Conversely, the ability to grow clean interfaces between materials has been a stepping stone for engineering built-in electric fields largely exploited in modern photovoltaics and opto-electronics. The emergence of atomically thin semiconductors is now enabling new ways to attain electric fields and unveil novel charge transport mechanisms. Here, we report the first direct electrical observation of the inverse charge-funnel effect enabled by deterministic and spatially resolved strain-induced electric fields in a thin sheet of HfS2. We demonstrate that charges driven by these spatially varying electric fields in the channel of a phototransistor lead to a 350% enhancement in the responsivity. These findings could enable the informed design of highly efficient photovoltaic cells.
This is the first experimental observation of the inverse charge funneling effect, that is a novel microscopic charge transport mechanism enabled by strain-induced electric fields. By developing a unique technique of photo-oxidation, we are able to engineer deterministic and spatially resolved strain patterns in ultra-thin films of HfS2 which in return generate built-in electric fields. Such strain gradient is responsible for the enhancement of the responsivity of a phototransistor of up to 350%, which was attributed to the inverse charge funnel effect. A simple analytical model was derived to simulate the SPCM experiments, which demonstrated the charge funnelling effect and allowed the determination of a long carrier recombination lifetime of 10−6 s in the strain-engineered region of the device. These results open the route towards the exploitation of strain-engineered devices for high-efficiency energy harvesting and sensing applications, with the potential to overcome the intrinsic limitations of current solar cells by exploiting both hot-carriers extraction and lossless transport, to achieve efficiencies approaching the thermodynamic limit in photovoltaic devices. The use of atomically thin materials could open the door to the incorporation of such devices in emerging wearable electronics technologies and smart buildings, creating a new paradigm in energy harvesting.