Electronic structure of polythieno[3,4-b]-thiophene-co-benzodithiophene (PTB7) derivatives for organic solar cell applications

• Prediction of new PTB7 derivatives properties for bulk-heterojunction solar cells.
• Chlorinated PTB7 shows frontier electronic levels energy very close to those reported as ideal to employ with PCBM.
• Chemical substitution in PTB7 apparently does not bring problems with exciton dissociation and recombination.

Among the new materials currently employed as electron donor element in active layers of organic solar cells (OSCs), PTB7 holds the best results. It has been extensively studied and now there is a search for new derivatives to improve its properties. In this work, a set of 24 polymers derived from polythieno[3,4-b]-thiophene-co-benzodithiophene (PTB7) was studied theoretically, using chemical modifications in the benzodithiophene (BDT) moiety of the PTB7 monomeric units. After evaluations of the electronic and optical properties, including the open circuit voltage and exciton dissociation and recombination conditions, the results indicate that employing chlorine as substituent yields the most promising material for application in active layers together with Phenyl-C61-Butyric-Acid-Methyl-Ester (PCBM) as electron acceptor material.

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