Wenkai Zhong's research while affiliated with Shanghai Jiao Tong University and other places

Non-fused ring electron acceptors (NFREAs) potentially have lower synthetic costs than their fused counterparts. However, the low backbone planarity and the presence of bulky substituents adversely affect the crystallinity of NFREAs, impeding charge transport and the formation of bicontinuous morphology in organic solar cells. Here we show that a binary solvent system can individually control the crystallization and phase separation of the donor polymer (for example, D18) and the NFREA (for example, 2BTh-2F-C2). We select solvents such as chloroform and o-xylene that evaporate at different temperatures and rates and have different solubility for D18. Upon evaporation of chloroform, D18 starts to assemble into fibrils. Then, the evaporation of o-xylene induces the rapid formation of a fibril network that phase segregates 2BTh-2F-C2 into pure domains and leads to a bicontinuous morphology. The well-defined interpenetrating network morphology affords an efficiency of 19.02% on small-area cells and 17.28% on 1 cm² devices.

Semitransparent organic photodetectors (ST‐OPDs) show immense promise for integration into optoelectronic devices, offering adjustable absorption and see‐through functionalities. However, achieving high‐performance ST‐OPDs remains challenging, necessitating a delicate balance of low dark current density, high external quantum efficiency, and optimal visible light transmission. Here, a strategy is presented using anode interfacial materials (AIMs) as the donor and narrow bandgap non‐fullerene acceptors (NFAs) to formulate the donor: acceptor light‐sensitive layer. Critical to the approach is the incorporation of 1,8‐diiodooctane during film processing, enabling the formation of morphology with an NFA molecular crystal network embedded within the donor polymer matrix. This optimized morphology substantially boosted device external quantum efficiency and reduced dark current under reverse bias, yielding a remarkable special detectivity of over 10¹³ Jones at 840 nm under a bias of −0.1 V. ST‐OPDs are achieved with detectivity surpassing 10¹² Jones and notable average visible transmittance of over 50%. These findings highlight the potential of AIM:NFA combinations for high‐efficiency ST‐OPDs by finely controlling morphology through multiple length scales, opening doors for various applications in transparent electronics and beyond.

Se‐functionalized small molecule acceptors (SMAs) exhibit unique advantages in constructing materials with near‐infrared absorption, but their photovoltaic performance lags behind that of S‐containing analogs in organic solar cells (OSCs). Herein, two new Se‐containing SMAs, namely Se‐EH and Se‐EHp, are designed and synthesized by regulating bifurcation site of outer alkyl chain, which enables Se‐EH and Se‐EHp to form different 3D crystal frameworks from CH1007. Se‐EH displays tighter π–π stacking and denser packing framework with smaller‐sized pore structure induced by larger steric hindrance effect of outer alkyl chain branched at 2‐position, and a higher dielectric constant of PM6:Se‐EH active layer can be obtained. OSCs based on PM6:Se‐EH achieved very high PCEs of 18.58% in binary and 19.03% in ternary devices with a high FF approaching 80% for Se‐containing SMAs. A more significant alkyl chain steric hindrance effect in Se‐EH adjusts the molecular crystallization to form a favorable nanofiber interpenetrating network with an appropriate domain size to reduce rate of sub‐ns recombination and promote balanced transport of carriers. This work provides references for further design and development of highly efficient Se‐functionalized SMAs.

Controlling the phase separation and domain purity of organic semiconductors to form well‐developed nanoscale morphology optimization in the bulk‐heterojunction active layer is critical yet challenging for building high‐performance organic photodetectors. Herein, an effective morphology controlling method by applying a small molecule IC‐Br as the solid additive is demonstrated, which can effectively restrict the overmix of the PTzBI‐Si:IEICO‐4F in the process of film formation. The film processed with IC‐Br formed well‐developed nanoscale phase separation with bi‐continuous interpenetrating networks, which exhibited enhanced π–π stacking and the improved domain purity of the IEICO‐4F phase, resulting in a significant decrease in the density of the trap state compared to the pristine film. Consequently, the device processed with IC‐Br additive enabled a high specific detectivity of 3.8 × 10¹³ Jones at 860 nm under −0.1 V associated with the improved linear dynamic range and response speed, indicating the strong visible‐to‐near infrared detecting capability and potential for practical applications. The morphology optimization strategy established in this work may offer unprecedented opportunities to build state‐of‐the‐art OPDs.

Organic photodetectors have attracted increasing attention in the scenario of low-cost imaging, health monitoring, and near-infrared sensing. However, relatively high dark current and trap density block the sensitivity for organic photodetectors. In this manuscript, a simple yet effective strategy is proposed to enhance the detectivity of organic photodetectors by incorporating a non-conjugated polymer additive of polystyrene into the functional layers. Systematic morphological investigation reveals that this strategy can not only enable suppressed amorphous phase but also effectively tune the phase separation in the bulk heterojunction blends. Electrical results suggest the suppressed trap density in optimized organic photodetectors. Consequently, a dark current density of 5.06 × 10−10 A cm−2 is achieved for PM6:Y6-BO-based organic photodetectors, showing a peak detectivity of 6.38 × 1013 cm Hz1/2 W−1 at 850 nm. This strategy is also applicable in various representative organic-semiconductor systems, including PTB7-Th:PC71BM and P3HT:PC61BM blends, superior to other optimization techniques.

With the rapid development of organic photovoltaics, device stability has become a crucial obstacle hindering their transition from laboratory to industrial applications. However, it remains still unclear how light differs...

Distributed photovoltaics in living environment harvest the sunlight in different incident angles throughout the day. The development of planer solar cells with large light-receiving angle can reduce the requirements in installation form factor and is therefore urgently required. Here, thin film organic photovoltaics with nano-sized phase separation integrated in micro-sized surface topology is demonstrated as an ideal solution to proposed applications. All-polymer solar cells, by means of a newly developed sequential processing, show large magnitude hierarchical morphology with facilitated exciton-to-carrier conversion. The nano fibrilar donor-acceptor network and micron-scale optical field trapping structure in combination contributes to an efficiency of 19.06% (certified 18.59%), which is the highest value to date for all-polymer solar cells. Furthermore, the micron-sized surface topology also contributes to a large light-receiving angle. A 30% improvement of power gain is achieved for the hierarchical morphology comparing to the flat-morphology devices. These inspiring results show that all-polymer solar cell with hierarchical features are particularly suitable for the commercial applications of distributed photovoltaics due to its low installation requirement.