Quantum of solar: new material's efficiency promise

C&I Issue 5, 2024

Read time: 2 mins


A new material made computationally could spark a leap forward in solar energy harvesting.

It taps into the concept of intermediate band solar cells – a technology that could revolutionise clean energy by boosting the conversion of sunlight to electrical energy.

Today, single-gap solar cells can reach around 32% conversion efficiency, whereas these new materials might vault to around 60% efficiency.

This could be achieved using intermediate band states, which are specific energy levels that are placed within the material’s electronic structure in a way that makes them suitable for energy conversion. ‘The most exciting result in our paper is the electronic structure of the material, which shows intermediate bands,’ notes Srihari Kastuar at Lehigh University in Pennsylvania, US.

These can capture some of the photon energy lost by traditional solar cells, including via reflection and heat. To develop their material, the physicists positioned atoms of zerovalent copper between layers of a two-dimensional material made of germanium selenide and tin sulfide (Science Advances, DOI: 10.1126/sciadv.adl6752).

‘Existing commercial solar cell materials have a single energy gap. Electrons are excited across this gap by light which has an equal or greater energy,’ explains Lucy Whalley, a materials physicist at Northumbria University, UK. Here, the researchers ‘use computational modelling to investigate an earth-abundant and low toxicity material which has effectively two energy gaps, allowing lower energy light in the sun’s spectrum to also be absorbed’.

Something called external quantum efficiency (EQE) is an important indicator for photovoltaic performance. It denotes the ratio of electrons generated to photons shining on a material. An EQE of 100% would mean that one electron is generated for each photon reaching a material.

The EQE predicted for the material reported by the Lehigh computational physicists was 190%, and ‘is possible through the relatively exotic process of multiple exciton generation, where one photon in can produce multiple electrons out,’ notes Whalley.

Nevertheless, she adds an important proviso: ‘This study is based on computational simulations, which always present an idealised version of real-life materials in the lab or in working devices.’ For example, we do not know the impact temperature might have on it.

‘The next step will be for experimentalists to synthesise the material,’ adds Whalley, and then use a range of techniques to verify the predictions.