Organic solar cells (OSCs) have experienced rapid development and achieved significant breakthroughs in power conversion efficiencies owing to the emergence of non-fullerene acceptors (NFAs) with ladder-type multiple fused ring structures. However, the high synthetic complexity and production cost of multiple fused ring NFAs hinder the commercial prospects of OSCs. In this context, the development of non-fused ring acceptors (NFRAs) with simple structures and facile synthesis has been proposed. In this mini review, we summarize the important progress in this field spanning from molecular design strategies to structure-performance relationships. Ultimately, with the aim of realizing the practical application of NFRAs in OSCs, we discuss the current challenges and future directions in terms of achieving high performance and low synthetic complexity simultaneously. These discussions provide valuable insights into the development of new NFRAs.

The development of polymer acceptors is critical to promote the power conversion efficiencies (PCEs) of all‐polymer solar cells (all‐PSCs). Herein, two novel polymer acceptors (PBTz–TT and PFBTz–TT) derived from non‐fused small molecules, which possess synthetic simplicity, narrow optical bandgap, and high absorption coefficients, are reported for the first time. The all‐PSCs are fabricated by a layer‐by‐layer deposition technique with PBDB‐T as donor, and the device performance is improved by the synergistic effect of solvent additive and thermal annealing. As a result, the all‐PSCs offer PCEs of 10.14% and 6.85% for PFBTz‐TT and PBTz‐TT, respectively. Further morphological and electrical characterizations unveil that the higher device performance of PFBTz‐TT originates from more efficient exciton separation and charge transport as a result of more ordered polymer packing in solid state. Herein, it is demonstrated that polymerizing non‐fused small molecular acceptors is an effective strategy to develop polymer acceptors for high‐performance all‐PSCs.

BNTT2F, an electron acceptor featuring B−N covalent bond and singlet-triplet gap as low as 0.20 eV via multiple resonance effect is developed for organic solar cells. The optimized device based...

It is known that the perovskite/hole transport layer (HTL) interface is a great limit to achieving high-performance perovskite solar cells (PSCs). Aiming to solve this problem, we introduce a naphthalene diimide (NDI)-based conjugated polymer bearing 3,4-difluorothiophene (PTzNDI-2FT) at the perovskite/HTL interface. We find that the PTzNDI-2FT interlayer combines multifunctions to passivate surface defects on the perovskite film, improve charge transport at the perovskite/HTL interface, and prevent penetration of the moisture and organic ion volatilization in the perovskite film. The champion device exhibits a power conversion efficiency of 23.2% under standard AM 1.5 G one sun illumination and offers excellent environmental, heat, and light stabilities.

Bulk heterojunction (BHJ) organic solar cells (OSCs) with p-type conjugated polymer as electron donor and n-type organic semiconductor as electron acceptor have attracted significant attention, on account of their advantages including low cost, flexibility, and semitransparency. [1] Stimulated by the development of non-fullerene acceptors (NFAs) and innovation of device engineering, the power conversion efficiencies (PCEs) of OSCs have exceeded 19%. [2] Highperformance polymer donors possessing complementary light absorption, matched energy levels, and appropriate thermodynamic miscibility with the prevailing NFAs have also played a critical role to this success. [3] To date, high-performance polymer donors are predominated by benzo[1,2-b:4,5-b′]dithiophene (BDT) polymers (Scheme S1a, Supporting Information), [4] such as PCE10, [5] PM6, [6] D18, [7] and PBCT-2F. [8] However, the raw chemical of BDT unit originates from petrochemical production (Scheme S1b, Supporting Information), [9] which still relies on nonrenewable resources. Compared with BDT, benzo[1,difuran (BDF) is more sustainable as it can be built from furfural, which is available from trees and vegetables (Scheme S1b, Supporting Information). [10] The biodegradable and biorenewable properties make BDF a more promising building block for polymer donors. [11] Moreover, the oxygen atom in BDF has smaller radius than the sulfur atom in BDT, which will endow the resultant polymers with more coplanar conjugated skeleton and more compact packing in solid state, [12] thus leading to improved film crystallinity and enhanced charge carrier mobility. [13] These merits suggest the promising prospect of BDF-based polymers for constructing high-performance OSCs. However, BDF-based polymers were much less developed in OSCs with respect to BDT-based polymers up to date. [12a,14] Compared with BDT-based polymers, BDF-based polymers usually exhibit too strong π-π interchain interaction and selfaggregation characteristics. This can be also ascribed to the smaller radius of oxygen atom in BDF with respect to sulfur atom in BDT unit. First, the twist angle between the peripheral The realization of high-efficiency organic solar cells (OSCs) from renewable sources will bring a real green energy technology. Benzo[1,2-b:4,5-b′]difuran (BDF) is such a building block for photovoltaic polymers as it can be built from furfural, which is available from trees and vegetables. However, the device performance of BDF-based polymers is limited by aggregation properties and unfavorable active layer morphology. Herein, two new BDF-based wide bandgap-conjugated polymers, PFCT-2F and PFCT-2Cl, are developed by copolymerizing the fluorinated or chlorinated BDF units with the 3-cyanothiophene unit for use as electron donors in OSCs. Benefitting from the more rotatable nature of the side-chain thiophene rings on the BDF unit, PFCT-2Cl exhibits more adjustable aggregation, higher π-π stacking ordering, and appropriate miscibility with the electron acceptor. As a result, a high power con...