Vince Lordi, Joel Varley, Kyoung Kweon

Collaborators:  Angus Rockett, Xiaoqing He (UIUC), Neil Mackie, Atiye Bayman, Geordie Zapalac, Tim Suen, Robert Tas (MiaSolé Hi-Tech), Peter Ercius (LBNL/NCEM), Robert Klie (Univ. of Illinois, Chicago), Aoki Toshihiro (Arizona State Univ.)

Thin-film solar cells using direct band gap active layer materials such as CuInGaSe₂ (CIGS) or CdTe can achieve high theoretical efficiencies with a small volume of material, but manufactured devices fall short with efficiencies below about 20%. One of the key efficiency bottlenecks is related to the use of CdS as a buffer layer—a layer deposited on top of the active material to protect the surface, but that should be transparent to sunlight. While CdS is currently found empirically to be the highest performance buffer layer material, its band gap is too small and absorbs a fraction of the solar spectrum without contributing useful photocurrent, thus imposing an efficiency penalty. We are working to understand the fundamental properties of CdS and other potential buffer layer materials, in terms of defects in the materials and properties of the interface with the active layer material, to enable the design of high performance wide band gap buffer layer materials. This collaborative project involves ab initio materials simulations to understand the atomic-scale nature of defects in the materials and their interfaces and the associated electronic properties, and also state-of-the-art aberration-corrected transmission electron microscopy to characterize the defects at the interface.

Funding from the DOE EERE BRIDGE/SunShot program is acknowledged.

Contact:  Vince Lordi