Three-fold improvement in the performance of all-polymer photovoltaic devices with graphene

• A blend of conjugated polymers (P3HT & F8BT) was used to make solar cells.
• Addition of graphene to the active layer results in a maximum of 200% increase in efficiency.
• A non-monotonic dependence of performance on graphene concentration and cell thickness is demonstrated.
• A greater extent of bimolecular recombination is observed with increasing grapheme concentration.

Solar cells fabricated from a blend of the conjugated polymers poly(3-hexylthiophene) (P3HT) and poly(9,9-dioctylfluorene-co-benzothiadiazole) (F8BT) demonstrate a substantial improvement in power conversion efficiency (η) upon the addition of pristine graphene to the active layer. Cells display complex dependence on graphene concentration, and a maximum of three-fold enhancement in performance. This increase is entirely due to the higher short circuit current (Jsc), since the open circuit voltage and fill factor are not affected. Cells also show greater bimolecular recombination with increasing graphene concentration. Device efficiency is demonstrated to be not only related to graphene content, but also to active layer thickness.