Kelvin Probe Force Microscopic Imaging of the Energy Barrier and Energetically Favorable Offset of Interfaces in Double-Junction Organic Solar Cells
详细信息 查看全文
- 作者：Mahbube K. Siddiki ; Swaminathan Venkatesan ; David Galipeau ; Qiquan Qiao
- 刊名：ACS Applied Materials & Interfaces
- 出版年：2013
- 出版时间：February 27, 2013
- 年：2013
- 卷：5
- 期：4
- 页码：1279-1286
- 全文大小：589K
- 年卷期：v.5,no.4(February 27, 2013)
- ISSN：1944-8252
文摘
A double-junction polymer solar cell (PSC) has attracted extensive attention as a promising approach to increasing efficiency. Tunneling/recombination interlayers between subcells play a critical role in double-junction PSCs. Interlayers include electron-transport layers (ETLs) such as Nb2O5, ZnO, and TiOx and hole-transport layers (HTLs) including PEDOT:PSS. These materials have all been used as interlayer materials, but it remains unclear which one is better than the other. Kelvin probe force microscopy (KFM) was used to identify the energy barrier and energetically favorable energy offset at the interfaces of acceptor鈥揈TL (e.g., PCBM鈥揘b2O5, PCBM鈥揨nO, and PCBM鈥揟iOx) and donor鈥揌TL (e.g., MDMO-PPV/PEDOT:PSS). Here the interface refers to the junction of two materials, formed by drop-casting one on top of other. The interface is buried and is therefore not accessible to the KFM probe. The energy barrier for electron transport from PCBM to ETL was found at 0.20, 0.12, and 0.012 eV at the PCBM鈥揘b2O5, PCBM鈥揨nO, and PCBM鈥揟iOx interfaces, respectively. Hole transport from the donor polymer to PEDOT:PSS was found to be energetically favorable with an energy offset of 0.14 eV to facilitate hole transport. The thickness independences of the energy barrier and energetically favorable energy offset at the interfaces of acceptor鈥揈TL and donor鈥揌TL were also observed. This work will provide guidance for researchers to identify and select appropriate materials as interlayers in double-junction PSCs.