Abstract
Indium tin oxide (ITO) is a transparent conductive material which is extensively used in organic solar cells (OSCs) as electrodes. In inverted OSCs, ITO is usually employed as a cathode, which should be modified by cathode buffer layers (CBLs) to achieve better contact with the active layers. In this paper, an amine group functionalized fullerene derivative (DMAPA-C60) is used as a CBL to modify the transparent cathode ITO in inverted OSCs based on PTB7 as a donor and PC71BM as an acceptor. Compared with traditional ZnO CBL, DMAPA-C60 exhibited comparable transmittance. OSCs based on DMAPA-C60 show much better device performance compared with their ZnO counterparts (power conversion efficiencies (PCEs) improved from 6.24 to 7.43%). This is mainly because a better contact between the DMAPA-C60 modified ITO and the active layer is formed, which leads to better electron transport and collection. Nanoscale morphologies also demonstrate that the surface of DMAPA-C60-modified ITO is plainer than the ZnO counterparts, which also leads to the better device performance.
Highlights
Bulk-heterojunction (BHJ) organic solar cells (OSCs) have been regarded as one of the most advanced photovoltaic technologies because of their advantages over traditional silicon solar cells, which include low cost, light weight, and flexibility [1,2,3,4]
We demonstrate that DMAPA-C60 can be independently used as a cathode buffer layers (CBLs) to modify the transparent conductive cathode Indium tin oxide (ITO) in inverted OSCs based on poly{4,8-bis[(2-ethylhexyl)oxy]benzo dithiophene-2,6-diyl-alt-3-fluoro-2-[(2-ethylhexyl)carbonyl]thieno[3,4,[3,4-b]thiophene-4,6-diyl} (PTB7)
An easy-accessible fullerene derivative, DMAPA-C60, was developed as a CBL to modify the transparent conducting cathode ITO in inverted OSCs based on a PTB7:PC71 BM system
Summary
Bulk-heterojunction (BHJ) organic solar cells (OSCs) have been regarded as one of the most advanced photovoltaic technologies because of their advantages over traditional silicon solar cells, which include low cost, light weight, and flexibility [1,2,3,4]. Inverted OSCs, which are mostly based on conductive indium tin oxides (ITO) as cathodes and silver (Ag) as anodes, possess major advantages of enhanced device performance as well as increased stability compared with conventional OSCs [10,11]. Electrode-semiconducting active layer contacts in organic electronics are plagued by interfacial barriers for charge transfer due to poor alignment between the electrode work function and the Fermi level of the semiconductor [13]. The cathode buffer layer (CBL) between the active layer and conductive ITO cathode plays an important role in the performance of inverted OSCs because it can decorate the ITO cathode and promote the electron transfer and extraction process [14,15]
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