@article{Nielsen:2015:10.1021/acs.accounts.5b00199,
author = {Nielsen, CB and Holliday, S and Chen, H and Cryer, S and Mcculloch, I},
doi = {10.1021/acs.accounts.5b00199},
journal = {Accounts of Chemical Research},
pages = {2803--2812},
title = {Non-fullerene electron acceptors for use in organic solar cells},
url = {http://dx.doi.org/10.1021/acs.accounts.5b00199},
volume = {48},
year = {2015}
}

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TY  - JOUR
AB  - The active layer in a solution processed organic photovoltaic device comprises a light absorbing electron donor semiconductor, typically a polymer, and an electron accepting fullerene acceptor. Although there has been huge effort targeted to optimize the absorbing, energetic, and transport properties of the donor material, fullerenes remain as the exclusive electron acceptor in all high performance devices. Very recently, some new non-fullerene acceptors have been demonstrated to outperform fullerenes in comparative devices. This Account describes this progress, discussing molecular design considerations and the structure–property relationships that are emerging.The motivation to replace fullerene acceptors stems from their synthetic inflexibility, leading to constraints in manipulating frontier energy levels, as well as poor absorption in the solar spectrum range, and an inherent tendency to undergo postfabrication crystallization, resulting in device instability. New acceptors have to address these limitations, providing tunable absorption with high extinction coefficients, thus contributing to device photocurrent. The ability to vary and optimize the lowest unoccupied molecular orbital (LUMO) energy level for a specific donor polymer is also an important requirement, ensuring minimal energy loss on electron transfer and as high an internal voltage as possible. Initially perylene diimide acceptors were evaluated as promising acceptor materials. These electron deficient aromatic molecules can exhibit good electron transport, facilitated by close packed herringbone crystal motifs, and their energy levels can be synthetically tuned. The principal drawback of this class of materials, their tendency to crystallize on too large a length scale for an optimal heterojunction nanostructure, has been shown to be overcome through introduction of conformation twisting through steric effects. This has been primarily achieved by coupling two units together, forming dimers
AU  - Nielsen,CB
AU  - Holliday,S
AU  - Chen,H
AU  - Cryer,S
AU  - Mcculloch,I
DO  - 10.1021/acs.accounts.5b00199
EP  - 2812
PY  - 2015///
SN  - 1520-4898
SP  - 2803
TI  - Non-fullerene electron acceptors for use in organic solar cells
T2  - Accounts of Chemical Research
UR  - http://dx.doi.org/10.1021/acs.accounts.5b00199
UR  - http://hdl.handle.net/10044/1/27672
VL  - 48
ER  - 

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