title: Strong and reversible modulation of carbon nanotube-silicon heterojunction solar cells by an interfacial oxide layer.
abstract: Deposition of nanostructures such as carbon nanotubes on Si wafers to make heterojunction structures is a promising route toward high efficiency solar cells with reduced cost. Here, we show a significant enhancement in the cell characteristics and power conversion efficiency by growing a silicon oxide layer at the interface between the nanotube film and Si substrate. The cell efficiency increases steadily from 0.5% without interfacial oxide to 8.8% with an optimal oxide thickness of about 1 nm. This systematic study reveals that formation of an oxide layer switches charge transport from thermionic emission to a mixture of thermionic emission and tunneling and improves overall diode properties, which are critical factors for tailoring the cell behavior. By controlled formation and removal of interfacial oxide, we demonstrate oscillation of the cell parameters between two extreme states, where the cell efficiency can be reversibly altered by a factor of 500. Our results suggest that the oxide layer plays an important role in Si-based photovoltaics, and it might be utilized to tune the cell performance in various nanostructure-Si heterojunction structures.
authors.affiliation: Graduate School at Shenzhen, Tsinghua University, Shenzhen, Guangdong Province, 518055, PR China.
authors.forename: Yi
authors.initials: Y
authors.lastname: Jia
authors.forename: Anyuan
authors.initials: A
authors.lastname: Cao
authors.forename: Feiyu
authors.initials: F
authors.lastname: Kang
authors.forename: Peixu
authors.initials: P
authors.lastname: Li
authors.forename: Xuchun
authors.initials: X
authors.lastname: Gui
authors.forename: Luhui
authors.initials: L
authors.lastname: Zhang
authors.forename: Enzheng
authors.initials: E
authors.lastname: Shi
authors.forename: Jinquan
authors.initials: J
authors.lastname: Wei
authors.forename: Kunlin
authors.initials: K
authors.lastname: Wang
authors.forename: Hongwei
authors.initials: H
authors.lastname: Zhu
authors.forename: Dehai
authors.initials: D
authors.lastname: Wu