Tailor-made synthesis of poly(3-hexylthiophene) with carboxylic end groups and its application as a polymer sensitizer in solid-state dye-sensitized solar cells

We report the first synthesis of regioregular poly(3-hexylthiophene) with carboxylic end groups (P3HT–COOH), show its potential to anchor onto mesoporous TiO2 and show its application as a polymer sensitizer in a solid-state dye-sensitized solar cell. The incorporation of COOH groups was done by a polymer analogous reaction on P3HT. The product is characterized in comparison with P3HT and low molecular weight model molecules of substituted thiophene. These model compounds are efficient tools to identify end groups in P3HT and P3HT–COOH. The solar cell with 2,2′,7,7′-tetrakis-(N,N-di-4-methoxyphenylamino)-9,9′-spiro-bifluorene (spiro-OMeTAD) as a hole conductor and P3HT–COOH as a polymer sensitizer on mesoporous TiO2 shows a short-circuit current of 3.7 mA cm−2, an open circuit voltage of 0.54 V and a power conversion efficiency of 0.9%.