By the introduction of different building blocks and side‐chains, a series of donor–acceptor type polymer acceptors containing naphthalene diimide have been successfully prepared. The theoretical and experimental results show that the molecular design effectively tunes the energy levels, solubility, and coplanarity of the acceptor polymers. The intermolecular packing, which has been considered as a key factor in the bulk heterojunction morphology, has been adjusted by changing the coplanarity. As a result of improved morphology and fine‐tuned energy levels, a power conversion efficiency of 6.0% has been demonstrated for the optimized devices, which is among the highest‐efficiencies for reported all‐polymer solar cells. The improved device performance may be attributed to the resemble crystallinity of the donor/acceptor polymers, which can lead to the optimal phase separation morphology balancing both charge transfer and transport.

No abstract

Schematic illustration of the dual function of C60–N on the perovskite layer: first, to reduce the work function of the Al electrode and second, to passivate the perovskite surface.

Ultrafast transient absorption (TA) spectroscopy was employed to investigate the thermal annealing effect on the charge transfer (CT) in bulk heterojunction (BHJ) all-polymer solar cells (all-PSCs) utilizing an n-type polymer P­(NDI2OD-T2) (Polyera, N2200) as acceptor and a low bandgap polymer PBPT as donor. The CT generates hole polarons residing in the PBPT and electron polarons belonging to N2200, manifested in the TA spectra of the BHJ films as the long-lived absorption peak centered at ∼850 nm. The CT is most efficient in the film annealed at 160 °C and its efficiency declines monotonically when enhancing or reducing the annealing temperature, displaying a positive correlation with the power conversion efficiency (PCE) of the corresponding solar cell devices. This correlation is analyzed in terms of the crystallinity and phase separation, which are the key factors determining the performance of all-PSCs. Our results can provide valuable guidance for the fabrication of BHJ all-PSCs to improve their PCE.

We have investigated a series of commercially available alkenyl carboxylic acids with different alkenyl chain lengths (trans-2-hexenoic acid (CA-6), trans-2-decenoic acid (CA-10), 9-tetradecenoic acid (CA-14)) for use as solvent additives in polymer-polymer non-fullerene solar cells. We systematically investigated their effect on the film absorption, morphology, carrier generation, transport, and recombination in all-polymer solar cells. We revealed that these additives have a significant impact on the aggregation of polymer acceptor, leading to improved phase segregation in the blend film. This in-depth understanding of the additives effect on the nanomorphology in all-polymer solar cell can help further boost the device performance. By using CA-10 with the optimal alkenyl chain length, we achieved fine phase separation, balanced charge transport, and suppressed recombination in all-polymer solar cells. As a result, an optimal power conversion efficiency (PCE) of 5.71% was demonstrated which is over 50% higher than that of the as-cast device (PCE = 3.71%) and slightly higher than that of devices with DIO treatment (PCE = 5.68%). Compared with widely used DIO, these halogen-free alkenyl carboxylic acids have a more sustainable processing as well as better performance, which may make them more promising candidates for use as processing additives in organic non-fullerene solar cells.