[특별 세미나 안내]
□ Topic : Improving Kesterite photovoltaics through Ag-alloying
□ Speaker : Dr. Talia Gershon (IBM)
□ Date : 2016년 4월 8일(금) 10:30 ~
□ Venue : 응용공학동 #2427 (Edu3.0 강의실)
□ Host : 신병하 교수
□ Abstract :
The photovoltaic absorber Cu2ZnSn(SxSe1-x)4 (CZTSSe) has attracted interest in recent years due to the earth-abundance of its constituents and the realization of high performance (12.6% efficiency). However, efficiency improvements in CZTSSe devices have been limited by the inability to increase the open-circuit voltage (Voc) beyond present values. In this talk, I will present evidence indicating that this shortfall in Voc is likely caused by band tailing in the absorber due to exceptionally high densities of Cu/Zn antisites. By replacing Cu in CZTSSe with Ag, whose covalent radius is ~15% larger than that of Cu and Zn, the density of I-II antisite defects is predicted to drop. I will discuss the fundamental properties of the mixed Ag-Cu kesterite compound as a function of Ag/(Ag+Cu) ratio. The extent of band tailing is shown to decrease with increasing Ag. Additionally, the pinning of the Fermi level in CZTSSe, attributed to heavy defect compensation and band tailing is not observed in the pure-Ag compound, offering further evidence of improved electronic structure. A device efficiency of 10.2% is presented for a device containing 10% Ag (no anti-reflection coating); this compares to ~ 9% (avg) efficiency for our baseline pure-Cu CZTSe.