TY - JOUR

T1 - Cyclopentadithiophene-benzothiadiazole copolymers with permutations of repeating unit length and ratios; synthesis, optical and electrochemical properties and photovoltaic characteristics

AU - Chang, S.W.

AU - Kettle, J.P.

AU - Waters, R.H.

AU - Horie, M.

N1 - Funding : National Science Council of Taiwan, 125 Scholarship from Bangor University.

PY - 2015/12/11

Y1 - 2015/12/11

N2 - Conjugated copolymers with varying ratios and lengths of cyclopentadithiophene (CPDT) to benzothiadiazole (BT) repeating units, -[(CPDT)(x)-(BT)(y)](n)-, have been synthesized by palladium complex catalysed Suzuki coupling polymerisation, direct arylation polymerisation or oxidative polymerisation using iron(III) chloride. The different permutations of the co-polymers allow for tuning of the optical and electrical properties. To our knowledge, this is one of the first studies of its kind for conjugated polymers for use in OPVs. The optical band gaps were measured between 1.7 and 2.0 eV in film, in which the polymer with ratios of CPDT : BT (x : y = 1 : 1) units showed the lowest bandgap followed by x : y = 1 : 2, 2 : 1, 2 : 2 and 3 : 3. Hole mobility and solar cell performance of these polymers with PC61BM as the electron acceptor were measured. A relatively small variation in hole mobility was observed between polymers. However, the best reported power conversion efficiency (PCE) was measured at 2.5% when processed in the absence of any additives using the polymer with ratios of CPDT : BT (x : y = 2 : 2), which was followed by the ratios of x : y = 2 : 1, 1 : 1, 1 : 2 and 3 : 3, indicating that variation of the ratios and length of donor and acceptor units affect OPV performance and better performance is achievable by careful consideration of the donor-to-acceptor ratio.

AB - Conjugated copolymers with varying ratios and lengths of cyclopentadithiophene (CPDT) to benzothiadiazole (BT) repeating units, -[(CPDT)(x)-(BT)(y)](n)-, have been synthesized by palladium complex catalysed Suzuki coupling polymerisation, direct arylation polymerisation or oxidative polymerisation using iron(III) chloride. The different permutations of the co-polymers allow for tuning of the optical and electrical properties. To our knowledge, this is one of the first studies of its kind for conjugated polymers for use in OPVs. The optical band gaps were measured between 1.7 and 2.0 eV in film, in which the polymer with ratios of CPDT : BT (x : y = 1 : 1) units showed the lowest bandgap followed by x : y = 1 : 2, 2 : 1, 2 : 2 and 3 : 3. Hole mobility and solar cell performance of these polymers with PC61BM as the electron acceptor were measured. A relatively small variation in hole mobility was observed between polymers. However, the best reported power conversion efficiency (PCE) was measured at 2.5% when processed in the absence of any additives using the polymer with ratios of CPDT : BT (x : y = 2 : 2), which was followed by the ratios of x : y = 2 : 1, 1 : 1, 1 : 2 and 3 : 3, indicating that variation of the ratios and length of donor and acceptor units affect OPV performance and better performance is achievable by careful consideration of the donor-to-acceptor ratio.

U2 - 10.1039/c5ra22946d

DO - 10.1039/c5ra22946d

M3 - Article

VL - 5

SP - 107276

EP - 107284

JO - RSC Advances

JF - RSC Advances

SN - 2046-2069

IS - 130

ER -