Understanding the Role of CdTe in Polycrystalline CdSexTe1–x/CdTe-Graded Bilayer Photovoltaic Devices

• Published in: Solar RRL Vol. 5; no. 11
• Main Authors: Shah, Akash, Pandey, Ramesh, Nicholson, Anthony, Lustig, Zach, Abbas, Ali, Danielson, Adam, Walls, John, Munshi, Amit, Sampath, Walajabad
• Format: Journal Article
• Language: English
• Published: United States Wiley 01.11.2021
• Subjects: CdTe; density functional theory; electron reflector; energy band alignment; ENERGY CONSERVATION, CONSUMPTION, AND UTILIZATION; MATERIALS SCIENCE; thin film solar cells; x-ray photoelectron spectroscopy
• ISSN: 2367-198X; 2367-198X
• DOI: 10.1002/solr.202100523

Grading of bandgap by alloying CdTe with selenium to form a CdSe x Te 1– x /CdTe‐graded bilayer device has led to a device efficiency over 19%. A CdSe x Te 1– x absorber would increase the short‐circuit current due to its lower bandgap but at the expense of open‐circuit voltage. It has been demonstrated that adding a CdTe layer at the back of such a CdSe x Te 1– x film reduces the voltage deficit caused by the lower bandgap of absorber from selenium alloying while maintaining the higher short‐circuit current. This leads to a photovoltaic device that draws advantage from both materials with an efficiency greater than either of them. Herein, a detailed account using device data, ultraviolet photoelectron spectroscopy, electron microscopy, and first‐principles density functional theory modeling is provided, which shows that CdTe acts as an electron reflector for CdSe x Te 1– x .