Side-chain engineering has been considered as one of the most promising strategies to optimize non-fullerene small-molecule acceptors (NFSMAs). Previous efforts were focused on the optimization of alkyl-chain length, shape, and branching sites. In this work, we propose that asymmetric side-chain engineering can effectively tune the properties of NFSMAs and improve the power conversion efficiency (PCE) for binary non-fullerene polymer solar cells (NFPSCs). Specifically, by introducing asymmetric side chains into the central core, both of the absorption spectra and molecule orientation of NFSMAs are efficiently tuned. When blended with polymer donor PM6, NFPSCs with EH-HD-4F (2-ethylhexyl and 2-hexyldecyl side chains) demonstrate a champion PCE of 18.38% with a short-circuit current density (J SC ) of 27.48 mA cm −2 , an open circuit voltage (V OC ) of 0.84 V, and a fill factor (FF) of 0.79. Further studies manifest that the proper asymmetric side chains in NFSMAs could induce more favorable face-on molecule orientation, enhance carrier mobilities, balance charge transport, and reduce recombination losses.

A new series of pyrenyl-capped benzofiurene derivatives (PFP-1, PFP-2, PFP-3, and PFP-4) were designed, synthesized, and investigated as model compounds for understanding the effects of flexible side chains on modulating the functional properties of organic semiconductors for optoelectronics. The resulting compounds exhibited high fluorescence yields (changing from 28% for PFP-1 to 46% for PFP-3), good thermal stability (increasing from 439 °C for PFP-4 to 510 °C for PFP-1), and fair glass-transition temperatures (ranging from 84 °C for PFP-4 to 175 °C for PFP-1). According to ultraviolet absorption (UV) and photoluminescence (PL) spectra, the long flexible side chains on diaryl substituents have played an important role on influencing the intermolecular interactions and radiative deactivation decays. Moreover, the flexible side chains on diaryl substituents also influence the process of exciton migration and exciton quenching, further resulting in different photoluminescence quantum yield (PLQY) and transient lifetimes for PFP-X. As evidenced by atomic force microscopy (AFM) images and X-ray diffraction (XRD) patterns, an increase in the lengths of flexible chain substituents can effectively depress the crystalline nature of the rigid conjugated molecular backbone, which can endow the corresponding materials with improved morphology properties. The solution-processed nondoped organic light-emitting diodes (OLEDs) based on PFP-3 showed high efficiency (up to 2.56 cd/A and 8372 cd/m2) and bright blue-light emission with Commission Intermationale de L’Eclairage (CIE) coordinates of (0.15, 0.15). It is worthwhile to mention that the performance of these solution-processed OLEDs is comparable to and even better than that of vacuum-deposited OLEDs. One-dimensional (1D) distributed feedback lasers using PFP-3 as gain media were constructed with a tunable wavelength ranging from 456.0 to 471.4 nm and low pump energy thresholds (0.28 KW/cm2), which is among the best results achieved from small molecular gain media. This study emphasizes that subtle structural alteration even for flexible side chains can significantly affect the corresponding characteristics, which are vital for rational design of the molecular structures for optoelectronic applications.

In the field of organic solar cells (OSCs), the interfacial layer plays the role of enhancing carrier extraction/ transportation, inhibiting their recombination, etc. In contrast to the wide variety of cathode interfacial materials with good modification ability, much less effort has been reported for anode interfacial materials. In this study, we report a polyoxometalatebased inorganic molecular cluster, zinc phosphotungstate (Zn 3 P 2 W 24 O 80 , denoted ZnPW), as an anode interfacial layer. Based on the PM6/EH-HD-4F/L8-BO-F ternary system, the device with ZnPW modification achieved a high power conversion efficiency (PCE) and a fill factor of up to 18.67 and 80.29%, respectively, which are higher than the counterpart device (PCE of 18.01%) with PEDOT/PSS as the anode interfacial layer. Detailed studies revealed that under the modification of ZnPW, the devices obtained promoted light absorption and suitable energy level matching between the active layer and the electrode, reduced contact resistance, and suppressed charge recombination. In addition, the ZnPW-modified devices had improved photostability and storage stability compared to PEDOT/PSS-modified devices. Our work shows that the polyoxometalate-based inorganic nanocluster ZnPW has great advantages in enhancing the device performance and stability of OSCs.

Five carbazole and diketopyrrolopyrrole-based donor-acceptor (D-A) new π-conjugated oligomers (π-COs) with gradually elongated lengths are facilely synthesized via a single pot of direct C–H arylation with merits of atom- and step-economy. The structure-property-performance correlations of these π-COs and their parent polymer are studied in detail by opto-electronic characterizations and bulk heterojunction (BHJ) organic photovoltaic (OPV) devices. It is found that the π-COs having longer lengths enable better performance in OPVs owing to the enhanced intermolecular interaction with the elongation of the conjugations. The above results not only highlight the powerful synthetic strategy here provided, but also reveal that π-COs with unique properties might find promising application in OPVs.