Speaker: Behrang Bagheri, ECpE Graduate Student
Advisor: Vikram Dalal
Title: Addressing the fundamental electronic properties of cadmium selenide (CdSe) material and making heterojunction solar cells
Abstract:CdSe is an important material with the potential to be a very good high bandgap partner with c-Si in a tandem cell arrangement. In this seminar, we investigate the fundamental optical and electronic properties of CdSe material, then make proof-of-concept heterojunction solar cells. Its bandgap is almost (1.72 eV) for a current match with c-Si in a tandem cell arrangement. Theoretical calculations indicate that it is possible to attain a thermodynamic efficiency of > 40% when a CdSe cell is deposited on top of a c-Si cell. CdSe is thermally stable and not water soluble with high absorption coefficient ~ 1.5×104cm-1. We discuss the growth of CdSe films using physical vapor deposition, and also discuss how to increase the grain size significantly up to 2um by using a cadmium chloride (CdCl2) post-treatment. Electron mobility in these films was measured using space charge limited current techniques (SCLC) and show values of ~ 3.5 cm2/V.S after grain enhancement. The device was an ideal heterojunction structure consisting of Glass/FTO/CdS(n+-type)/CdSe(n-type)/Organic(p+-layer)/Top, where Top could be NiOx/ITO or Gold. The electron transport laser (ETL) acted to prevent hole recombination at the n+/n interface and hole transport layer (HTL) acted to prevent electron recombination at the p+/n interface. We show 0.8V of open circuit voltage for the superstrate device, also higher quantum efficiency current for substrate device.