• Energy Research

AbstractThree novel copolymers based on zigzag naphthodithiophene (zNDT) with different aromatic rings as π bridges and different core side substitutions are designed and synthesized (PzNDT‐T‐1,3‐bis(4‐(2‐ethylhexyl)‐thiophen‐2‐yl)‐5,7‐bis(2‐ethylhexyl)benzo[1,2‐c:4,5‐c′]‐dithiophene‐4,8‐dione (BDD), PzNDT‐TT‐BDD, and PzNDTP‐T‐BDD, respectively). The 2D conjugation structure and molecular planarity of the polymers can be effectively altered through the modification of conjugated side chains and π‐bridges. These alterations contribute to the variation in energy levels, light absorption capacity, and morphology compatibility of the polymers. When blended with the nonfullerene acceptor (2,2′‐[(4,4,9,9‐tetrahexyl‐4,9‐dihydro‐sindaceno[1,2‐b:5,6‐b′]dithiophene‐2,7‐diyl)bis[methylidyne(3‐oxo‐1H‐indene‐2,1(3H)‐diylidene)]]bis‐propanedinitrile) (IDIC), PzNDT‐T‐BDD exhibits the highest power conversion efficiency (PCE) of 9.72% among the three polymers. This result can be attributed to its superior crystallinity and more obvious face‐on orientation in blending film. PzNDT‐TT‐BDD and PzNDTP‐T‐BDD present PCE values of 8.20% and 4.62%, respectively. The alteration of polymer structure, particularly the modification of conjugated side chains and π‐bridges, is an effective strategy for designing NDT‐based polymers with high photovoltaic performance and potential applications in fullerene‐free solar cells.

AbstractOrganic solar cells based on semiconducting polymers and small molecules have attracted considerable attention in the last two decades. Moreover, the power conversion efficiencies for solution‐processed solar cells containing A–π–D–π–A‐type small molecules and fullerenes have reached 11%. However, the method for designing high‐performance, photovoltaic small molecules still remains unclear. In this review, recent studies on A–π–D–π–A electron‐donating small molecules for organic solar cells are introduced. Moreover, the relationships between molecular properties and device performances are summarized, from which inspiration for the future design of high performance organic solar cells may be obtained.

A 2D–3D perovskite, in which 3D perovskite phase is bridged by 2D perovskite having periodically repeated vertical orientation is reported. It's PCE and stability is better than 3D MAPbI3 and it is an excellent structural strategy to improve stability of perovskite solar cells.

Y-type acceptors exhibiting faster migration (shorter τ) of local excitons (LEs) in disordered regions of aggregates to intermolecular charge-transfer (ICT) excitons in ordered regions can achieve higher efficiencies in organic solar cells.

AbstractTwo novel benzo[1,2‐b:4,5‐b′ ]difuran (BDF)‐based wide‐bandgap polymers, PBDFT‐FBz and PBDFF‐FBz, featuring a difluorobenzotriazole (FBz) acceptor unit, are designed and synthesized. The first attempt through main‐chain engineering to alter thiophene units to furan units in the main chain of PBDFT‐FBz, and further side‐chain engineering eliminate the 2‐ethylthiophenyl side chains of PBDFT‐FBz by 2‐ethylfuryl side chains to generate the “all‐furan” polymer PBDFF‐FBz. By taking the benefit of the oxygen atom in furan, both PBDFT‐FBz and PBDFF‐FBz exhibit lower HOMO energy levels and enhanced polymer chain interactions compared to their benzo[1,2‐b:4,5‐b′ ]dithiophene (BDT)‐based counterparts. As a result, while applying both polymers in non‐fullerene polymer solar cells with non‐fullerene acceptor m‐ITIC, both devices exhibit highly promising photovoltaic performance. The power conversion efficiency (PCE) in the PBDFT‐FBz device reaches 7.57% with increased open circuit voltage (Voc) and fill factor (FF) compared to the PCE of 5.98% in its BDT counterpart (J52). A further increased PCE is obtained (8.79%) in the PBDFF‐FBz:m‐ITIC device, which shows ≈47% enhancement in device performance compared to that of J52. The large increase in photovoltaic performance is attributed to the lower‐lying HOMO energy levels and better chain interactions in these BDF‐based polymers.