Project Name: 15%-Efficiency (Mg,Zn)CdTe Solar Cells with 1.7 eV Bandgap for Tandem Applications
Funding Opportunity: PVRD
SunShot Subprogram: Photovoltaics
Location: Tempe, AZ
SunShot Award Amount: $400,000
Awardee Cost Share: $44,455
Project Investigator: Zachary Holman

This project aims to demonstrate solar cells based on wide bandgap cadmium telluride (CdTe) alloys that will eventually enable the fabrication of high efficiency tandem photovoltaic (PV) cells in combination with a silicon bottom cell. The PV market is dominated by silicon and CdTe technologies, which have become low-cost and reliable in the last decade but are nearing their individual efficiency limits. This project works to boost the eventual efficiency of PV systems by 35% by beginning the process of allowing CdTe and silicon to function together to efficiently harvest the solar spectrum.


The overall objective of this project is to demonstrate a 15%-efficient (Mg,Zn)CdTe solar cell with a bandgap of 1.7–1.9 eV. This cell will be a critical first step toward market-competitive flat-plate modules with efficiencies significantly higher than single-junction silicon or thin-film modules. (Mg,Zn)CdTe promises to be the optimum top cell for pairing with silicon in a tandem due to the projected low cost and long-term stability that other top-cell candidates don’t have. To reach 15% efficiency, this project specifically aims to develop high-quality (Mg,Zn)CdTe absorbers with minimized non-radiative recombination, as well as effective heterojunction contacts. Absorber layers and heterojunction contacts will be developed in parallel using molecular beam epitaxy and close-space sublimation growth to target high performance devices in the lab and transfer project results to the solar industry.


By developing a robust and low cost top cell, this project will demonstrate the first step toward disrupting the residential PV industry with low-cost tandem modules. Pairing silicon and CdTe-based top cells to create tandem technology could result in 27% efficient cells enable a 20% decrease in the cost of installed systems, reducing the levelized cost of electricity to $0.03 per kilowatt hour by 2030.