Background

Thin film photovoltaics, specifically those based on polycrystalline CuIn(1‑x)Ga(x)Se2 (CIGS), have great potential as low‑cost, high‑throughput solar energy harvesting devices. However, current state of the art CIGS devices demonstrate power conversion efficiencies of 15‑18%, whereas the theoretical maximum is 28%. This lack efficiency is mainly due to the quality of the non‑active top layers responsible for charge‑collection, electric‑field formation, and passivation. Although the materials that make up these layers have high optical transmission with longer wavelengths, they tend to have unwanted optical absorption with shorter wavelengths, which reduces the amount of light transmitted onto the CIGS active layer. In order to realize the potential of this technology, there is a need to improve the performance of these top layers to increase the overall power conversion efficiency while maintaining or decreasing the material and production cost.

Technology

Researchers at Stony Brook University (SBU) propose a solution which replaces the multiple top layers with a single optically transparent and highly conductive graphene layer. The graphene Fermi level can be tuned via doping, allowing optimization of the CIGS active layer composition and eliminating unwanted optical absorption in the top layers. This new discovery of n‑doping graphene that has been transferred onto CIGS has allowed control over doping strength and thus control over graphene work function.

Advantages

Reduced parasitic optical absorption of top layers - Tunable doping of graphene

Application

Semiconductor devices - Solar cells - Photovoltaic cells - Solar energy harvesting