EAGER: Novel high bandgap inorganic solar cell for tandem junction cells with CdTe

Photovoltaic (PV) technology is now the fastest growing energy technology in the world, with over 1600 GW being installed worldwide. Photovoltaic energy technology lasts 30+ years with little maintenance. This project is focused on improving its efficiency at converting solar energy into electricity.

Two concerns with PV technology are that the conversion efficiency remains low in commercial panels, at about 20%, and that 90% of the panels are made from Si, where China has a stranglehold on raw Si, with 98% of raw Si coming from China. This is a national security concern. PV Technology based on CdTe is a promising alternative to Si, but it needs a higher efficiency to reduce costs.

In this project, we propose investigating a new material system, an alloys of CdSe and CdS, and a novel device structure to make high efficiency tandem cells. Simulations show that the new device, in a tandem cell arrangement with the currently produced CdTe solar cells, is capable of making 35% efficiency cells without using Si, thereby increasing the efficiency of CdTe solar cells by about 40%.

The new PV material system is an alloy of CdS and CdSe [Cd(S, Se)] whose bandgap can be varied by changing the S:Se ratio. We are aiming to develop a PV material with a bandgap of ~2-2.1 eV which will act as the appropriate material for the higher gap cell with the existing Cd(Se,Te) cell acting as the lower gap cell in a 4-terminal tandem cell arrangement.

Simulations show that when combined with Cd(Se,Te) as the bottom cell, the new PV device, when optimized, can produce devices with 35+% conversion efficiency in production, a potential efficiency breakthrough for the Cd(Se,Te) technology which is currently the major thin film PV technology. The proposed technology does not use Si and is manufacturable using a technology (CSVT) similar to the currently used technology for Cd (Se,Te) cells.

The research will focus on developing PV devices in the new material system [Cd(S,Se)]. The new material is a direct bandgap material with high absorption coefficient and thus, we can make thin film PV devices in a manner similar to devices in CdSe or CdTe. In the project, we will use appropriate p-type heterojunction materials such as p-a(Si,C):H and NiO to make p-n junction devices.

Fundamental measurements of material and device properties will be an integral part of the project. The project will provide opportunities for education and research training of both graduate students and a post-doctoral researcher. The results will be disseminated in open literature and at scientific conferences.

This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.