Manipulating the donor:acceptor (D:A) energetics, e.g. the highest occupied molecular orbital (HOMO) offset, is the key to balancing the charge separation and charge recombination for high-performance organic solar cells (OSCs)....

We find that conjugated polymers can undergo reversible structural phase transitions during electrochemical oxidation and ion injection.We study poly[2,5-bis(thiophenyl)-1,4-bis(2-(2-(2methoxyethoxy)ethoxy)ethoxy)benzene] (PB2T-TEG), a conjugated polymer with glycolated side chains. Using grazing incidence wide angle X-ray scattering (GIWAXS), we show that, in contrast to previously known polymers, this polymer switches between two structurally distinct crystalline phases associated with electrochemical oxidation/reduction in an aqueous electrolyte. Importantly, we show that this unique phase change behavior has important physical consequences for ion transport. Notably, using moving front experiments visualized by both optical microscopy and super-resolution photoinduced force microscopy (PiFM), we show that a propagating ion front in PB2T-TEG exhibits non-Fickian transport, retaining a sharp step-edge profile, in stark contrast to the Fickian diffusion more commonly observed. This structural phase transition is reminiscent of those accompanying ion uptake in inorganic materials like LiFePO 4 . We propose that engineering similar properties in future conjugated polymers may enable the realization of new materials with superior performance in electrochemical energy storage or neuromorphic memory applications.

Organic electrochemical transistors (OECTs) are currently being developed for applications ranging from bioelectronics to neuromorphic computing. We show that fullerene derivatives with glycolated side chains can serve as n-type active layers for OECTs with figures of merit exceeding the best reported conjugatedpolymer-based n-type OECTs. By comparing two different fullerene derivatives, [6,6]phenyl-C 61 -butyric acid methyl ester (PCBM) and 2-(2,3,4-tris(methoxtriglycol) phenyl) [60]fulleropyrrolidine (C60-TEG), we find that the hydrophilic glycolated side chains in C60-TEG enable volumetric doping of C60-TEG films. In contrast, the hydrophobic nature of PCBM prevents ions from penetrating into the material. Our results demonstrate that small-molecule semiconductors follow many of the same design principles established for conjugated polymers and can function as highperforming mixed electronic/ionic conductors for efficient, fast OECTs.

Organic solar cells (OSCs) with visible transparency and vivid colors are promising for deployment in building-integrated photovoltaics (BIPVs), yet significant challenges remain to be addressed for not only balancing the trade-off between the photovoltaic and optical properties but also controlling the bandpass of visible transmittance for the coloration of semitransparent OSCs (ST-OSCs). Herein ST-OSCs with vivid colors are successfully developed by employing one fixed active blend in the rationally designed device layout with a high-quality Fabry−Peŕot electrode. With the assistance of optical simulation, vividly colorful ST-OSCs have been obtained with power conversion efficiency of >14% and maximum transmittance up to 31%. Overall, this study provides new access to OSCs with promising features as BIPVs.

An organic solar cell (OSCs) containing double bulk heterojunction (BHJ) layers, namely, double-BHJ OSCs is constructed via stamp transferring of low bandgap BHJ atop of mediate bandgap active layers. Such devices allow a large gain in photocurrent to be obtained due to enhanced photoharvest, without suffering much from the fill factor drop usually seen in thick-layer-based devices. Overall, double-BHJ OSC with optimal ≈50 nm near-infrared PDPP3T:PC BM layer atop of ≈200 nm PTB7-Th:PC BM BHJ results in high power conversion efficiencies over 12%.

High-performance organic solar cells (OSCs) at the current stage are majorly accomplished from the processing of halogenated solvents, such as chloroform, which will be constrained for upscale fabrication due to the adverse health and environmental impacts. Therefore, exploring the high-performance OSCs from non-halogenated solvent processing becomes highly necessary, yet largely lagged behind. Herein, it is demonstrated high-performance OSCs can be obtained from the hot spin processing of different non-halogenated solvents, and achieve the highest reported efficiency of OSCs from nonhalogenated solvent processing so far. It is revealed that the phase evolution of ternary blends during solution-to-solid transition has a correlation to the substrate temperature. With the elevated substrate temperature of hot spin coating, the optimal blend films can be secured in different kinds of non-halogenated solvents. As result, high-performance OSCs are obtained with excellent power conversion efficiencies of 18.25% in o-xylene, 18.20% in p-xylene, and 18.12% in toluene, respectively. To the author's best knowledge, these results represent the best-performed OSCs made from non-halogenated solvents so far.

Efficiently converting invisible light while allowing full visible light transmission is key to achieving high‐performance semitransparent organic photovoltaics (ST‐OPVs). Here, a detailed balance strategy is explored to optimize the ST‐OPV via taking both absorption and carrier dynamics into consideration. Based on this principle, comprehensive optimizations are carried out, including a ternary strategy, donor:acceptor blend ratio, thickness, antireflection, etc., to compromise the invisible energy conversion and visible transmission for high‐performance ST‐OPVs. As a result, the opaque OPV device exhibits a champion power conversion efficiency of 19.35% (certificated 19.07%), and most strikingly, the best ST‐OPV shows a remarkably high light‐utilization efficiency of 5.0%, where the efficiency and the average visible transmission are 12.95% and 38.67%, respectively. An efficiency of 12.09% is achieved on the upscaled device with an area of 1.05 cm2, demonstrating its promise for large‐area fabrication. These results are among the best values for ST‐OPVs. Besides, it is demonstrated that the ST‐OPV exhibits good infrared light‐reflection capability for thermal control. This work provides a rational design of balancing the absorbing selectivity and photon‐to‐electron conversion for high‐performance ST‐OPVs, and may pave the way toward the practical application of solar windows.

Solar energy conversion has nowadays attracted research interests of the community, wherein conjugated polymers (CPs) become a class of workhorses on photon-to-electron and photon-to-fuel conversion studies. In recent years, exciting breakthroughs have been made in these multi-interdisciplinary fields, with the assistance of the intrinsic flexibilities on tuning optoelectronic, mechanical and structural properties of CPs. In this review, we summarize the recent notable development of CPs in polymer solar cells, perovskite solar cells, and photocatalysts, wherein CPs function well as light-capture and conversion components for polymer solar cells and photocatalysts as well as charge extraction materials for perovskite solar cells. By analyzing the principles, status, and structural-properties of these areas, we outline the design strategies and perspectives of CPs for further advancing solar energy conversions.