US researchers have designed a 2D solar cell based on TMDC that can clearly exceed the efficiency of this device typology, which usually does not exceed 6%. The novelty of this cell consists of its superlattice structure, which, according to the research team, allows the layers of 2D TMDCs to be separated by a spacer, which improves light absorption.
TMDCs are two-dimensional materials with remarkable semiconducting properties and high optical absorption coefficientfithey are suitable for the fabrication of semi-transparent and flexible solar cells that can be used in aerospace, architecture, electric vehicles and wearable electronics, where light weight, high power-to-weight ratio and flexibility are highly desirable. .
“I think people are slowly realizing that 2D TMDCs are excellent photovoltaic materials, although not for terrestrial applications, but for applications that are mobile – more flexible, such as space-based applications,” said lead author Deep Jariwala. “The weight of 2D TMDC solar cells is 100 times less than silicon or gallium arsenide solar cells, so suddenly these cells become a very attractive technology.”
The scientists built the cell with a single-layer absorber made of molybdenum disulfide (MoS2), a 3 nm insulator based on aluminum oxide (Al2O3) placed on a substrate made of Al2O3 and gold (Au), the latter acting as a reflector. “Thickness of Al2O3 layer is optimized to enhance photocarrier production,” they explained. “The active layer of the device is native and 0.98 μm long, and the silver and gold cathode and anode electrodes are 0.01 μm long.”
According to the researchers, the novelty of this cell consists of its superlattice structure, which they say can separate layers of 2D TMDCs with a spacer or non-semiconductor layer. “With the partition of the layers, you can bounce light many, many times inside the cell structure, even if the cell structure is very thin,” Jariwala said, noting that the cell has large exciton binding energies.
When tested in a series of simulations, the proposed cell structure with separate contacts was able to achieve a power conversion efficiency of 12.87%. By comparison, real 2D TMDC solar cells have so far been able to achieve an efficiency of up to 6%.
“We didn’t expect to see a value of 12% for such thin cells. Given that current efficiencies are below 5%, I hope that in the next 4-5 years people can actually demonstrate cells with 10% efficiency and above,” the researchers stated.
They described the new cell technology in the paper “How good can 2D excitonic solar cells be?” published device. “Our results demonstrate that 2D TMDC-based solar glasses, when optimized for both optical and electronic design, offer superior performance compared to other thin-film materials in terms of power density, which is vital for many applications such as aerospace, remote sensing, and wearable technology,” they concluded.