A low band gap, solution processable oligothiophene with a dialkylated diketopyrrolopyrrole chromophore for use in bulk heterojunction solar cells

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Abstract
Bulk heterojunction solar cells are fabricated from blends of oligothiophene with a dialkylated diketopyrrolopyrrole chromophore:[6,6]-phenyl C 71 butyric acid methyl ester. Absorption and photocurrent of the films extend to 800 nm. A power conversion efficiency (PCE) of 3.0% is obtained under simulated 100 mW / cm 2 AM1.5 illumination with a 9.2 mA / cm 2 short-circuit current density and an open-circuit voltage of 0.75 V. The hole and electron mobilities in the 50:50 blend are fairly balanced, 1.0 × 10 − 4 and 4.8 × 10 − 4 cm 2 / V s , respectively. This is the highest PCE reported to date for solar cells using solution processable small molecules.