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On the Relationship Between Donor/Acceptor Interface Energy Levels and Open‐Circuit Voltages
Author(s) -
Li Peicheng,
Hong Weiji,
Li Yiying,
Ingram Grayson,
Lu ZhengHong
Publication year - 2017
Publication title -
advanced electronic materials
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 2.25
H-Index - 56
ISSN - 2199-160X
DOI - 10.1002/aelm.201700115
Subject(s) - heterojunction , open circuit voltage , materials science , acceptor , planar , optoelectronics , photovoltaic system , offset (computer science) , voltage , photoemission spectroscopy , work function , nanotechnology , spectral line , electrical engineering , computer science , physics , condensed matter physics , computer graphics (images) , layer (electronics) , programming language , engineering , astronomy
Energy offset ( E DA ) from a number of donor/acceptor heterojunctions is measured using ultraviolet photoemission spectroscopy. It is found that substrate work functions have little impact on the energy level alignments at donor/acceptor heterojunctions. Planar‐heterojunction organic photovoltaic cells are made to test the relationship between energy offset and open‐circuit voltage ( V OC ). V OC is found to increase linearly as a function of E DA . The V OC , however, takes a surprising turn at E DA = 1.5 eV and starts to decrease as a function of donor–acceptor energy levels. To explain this experimental observation, a theoretical model to quantify the relationship between V OC and E DA is developed. The proposed model well explains the experimental data and, in particular, the reverse trend of V OC on E DA . By grouping several material constants into one variable, a simple universal plot that well describes the experimental data for both planar‐heterojunction and bulk‐heterojunction cells is generated.