Search

This study has proposed to use a well-defined oligomer F4TBT4 to replace its analogue polymer as electron acceptor toward tuning the phase separation behavior and enhancing the photovoltaic performance of all-polymer solar cells. It has been disclosed that the oligomer acceptor favors to construct pure and large-scale phase separation in the polymer:oligomer blend film in contrast to the polymer:polymer blend film. This gets benefit from the well-defined structure and short rigid conformation of the oligomer that endows it aggregation capability and avoids possible entanglement with the polymer donor chains. The charge recombination is to some extent suppressed and charge extraction is also improved. Finally, the P3HT:F4TBT4 solar cells not only output a high VOC above 1.2 V, but also achieve a power conversion efficiency of 4.12%, which is two times higher than the P3HT:PFTBT solar cells and is comparable to the P3HT:PCBM solar cells. The strategy of constructing optimum phase separation with oligomer to replace polymer opens up new prospect for the further improvement of the all-polymer solar cells. [ABSTRACT FROM AUTHOR]

For polymer solar cells (PSCs) with conventional configuration, the vertical composition profile of donor:acceptor in active layer is detrimental for charge carrier transporting/collection and leads to decreased device performance. A cross-linkable donor polymer as the underlying morphology-inducing layer (MIL) to tune the vertical composition distribution of donor:acceptor in the active layer for improved PSC device performance is reported. With poly(thieno[3,4- b]-thiophene/benzodithiophene):[6,6]-phenyl C71-butyric acid methyl ester (PTB7:PC71BM) as the active layer, the MIL material, PTB7-TV, is developed by attaching cross-linkable vinyl groups to the side chain of PTB7. PSC device with PTB7-TV layer exhibits a power conversion efficiency (PCE) of 8.55% and short-circuit current density ( JSC) of 15.75 mA cm−2, in comparison to PCE of 7.41% and JSC of 13.73 mA cm−2 of the controlled device. The enhanced device performance is ascribed to the much improved vertical composition profile and reduced phase separation domain size in the active layer. These results demonstrate that cross-linked MIL is an effective strategy to improve photovoltaic performance of conventional PSC devices. [ABSTRACT FROM AUTHOR]

The morphology with the interpenetrating network and optimized vertical phase separation plays a key role in determining the charge transport and collection in polymer:nonfullerene small molecular acceptors (SMAs) solar cells. However, the crystallization of polymer and SMAs usually occurs simultaneously during film‐forming, thus interfering with the crystallization process of each other, leading to amorphous film with undesirable lateral and vertical phase separation. The poly(3‐hexylthiophene) (P3HT):O‐IDTBR blend is selected as a model system, and controlling film‐forming kinetics to solve these problems is proposed. Herein, a cosolvent 1,2,4‐triclorobenzene (TCB) with selective solubility and a high boiling point is added to the solution, leading to prior crystallization of P3HT and extended film‐forming duration. As a result, the crystallinity of both components is enhanced significantly. Meanwhile, the prior crystallization of P3HT induces solid–liquid phase separation, hence rationalizing the formation of the nano‐interpenetrating network. Moreover, the surface energy drives O‐IDTBR to enrich near the cathode and P3HT to migrate to the anode. Consequently, a highly crystalline nano‐interpenetrating network with proper vertical phase separation is obtained. The optimal morphology improves charge transport and suppresses bimolecular recombination, boosting the power conversion efficiency from 4.45% to 7.18%, which is the highest performance in P3HT‐based binary nonfullerene solar cells. [ABSTRACT FROM AUTHOR]