Imperial College London


Faculty of Natural SciencesDepartment of Physics

Visiting Professor



+44 (0)20 7594 6669thomas.anthopoulos Website




Mrs Carolyn Dale +44 (0)20 7594 7579




1111Blackett LaboratorySouth Kensington Campus






BibTex format

author = {Casey, A and Dimitrov, SD and Shakya-Tuladhar, P and Fei, Z and Nguyen, M and Han, Y and Anthopoulos, TD and Durrant, JR and Heeney, M},
doi = {10.1021/acs.chemmater.6b02030},
journal = {Chemistry of Materials},
pages = {5110--5120},
title = {Effect of Systematically Tuning Conjugated Donor Polymer Lowest Unoccupied Molecular Orbital Levels via Cyano Substitution on Organic Photovoltaic Device Performance},
url = {},
volume = {28},
year = {2016}

RIS format (EndNote, RefMan)

AB - We report a systematic study into the effects of cyano substitution on the electron accepting ability of the common acceptor 4,7-bis(thiophen-2-yl)-2,1,3-benzothiadiazole (DTBT). We describe the synthesis of DTBT monomers with either 0, 1, or 2 cyano groups on the BT unit and their corresponding copolymers with the electron rich donor dithienogermole (DTG). The presence of the cyano group is found to have a strong influence on the optoelectronic properties of the resulting donor–acceptor polymers, with the optical band gap red-shifting by approximately 0.15 eV per cyano substituent. We find that the polymer electron affinity is significantly increased by ∼0.25 eV upon addition of each cyano group, while the ionization potential is less strongly affected, increasing by less than 0.1 eV per cyano substituent. In organic photovoltaic (OPV) devices power conversion efficiencies (PCE) are almost doubled from around 3.5% for the unsubstituted BT polymer to over 6.5% for the monocyano substituted BT polymer. However, the PCE drops to less than 1% for the dicyano substituted BT polymer. These differences are mainly related to differences in the photocurrent, which varies by 1 order of magnitude between the best (1CN) and worst devices (2CN). The origin of this variation in the photocurrent was investigated by studying the charge generation properties of the photoactive polymer–fullerene blends using fluorescence and transient absorption spectroscopic techniques. These measurements revealed that the improved photocurrent of 1CN in comparison to 0CN was due to improved light harvesting properties while maintaining a high exciton dissociation yield. The addition of one cyano group to the BT unit optimized the position of the polymer LUMO level closer to that of the electron acceptor PC71BM, such that the polymer’s light harvesting properties were improved without sacrificing either the exciton dissociation yield or device VOC. We also identify that the dr
AU - Casey,A
AU - Dimitrov,SD
AU - Shakya-Tuladhar,P
AU - Fei,Z
AU - Nguyen,M
AU - Han,Y
AU - Anthopoulos,TD
AU - Durrant,JR
AU - Heeney,M
DO - 10.1021/acs.chemmater.6b02030
EP - 5120
PY - 2016///
SN - 0897-4756
SP - 5110
TI - Effect of Systematically Tuning Conjugated Donor Polymer Lowest Unoccupied Molecular Orbital Levels via Cyano Substitution on Organic Photovoltaic Device Performance
T2 - Chemistry of Materials
UR -
UR -
VL - 28
ER -