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The power conversion efficiencies (PCEs) of flexible organic solar cells (OSCs) still lag behind those of rigid devices and their mechanical stability is unable to meet the needs of flexible electronics at present due to the lack of a high‐performance flexible transparent electrode (FTE). Here, a so‐called “welding” concept is proposed to design an FTE with tight binding of the upper electrode and the underlying substrate. The upper electrode consisting of solution‐processed Al‐doped ZnO (AZO) and silver nanowire (AgNW) network is well welded by utilizing the capillary force effect and secondary growth of AZO, leading to a reduction of the AgNWs junction site resistance. Meanwhile, the poly(ethylene terephthalate) is modified by embedding the AgNWs, which are then used to link with the AgNWs in the upper hybrid electrode, thus enhancing the adhesion of the electrode to the substrate. By this welding strategy, critical bottleneck issues relating to the FTEs in terms of optoelectronic and mechanical properties are comprehensively addressed. The single‐junction flexible OSCs based on this welded FTE show a high performance, achieving a record high PCE of 15.21%. In addition, the PCEs of the flexible OSCs are less influenced by the device area and display robust bending durability even under extreme test conditions.

of semitransparent organic solar cells (ST-OSCs) with transparent facilities, such as building windows, automobile glass, and greenhouse rooftops, is of particular interest, since it opens up the prospect of employing the facade for solar-power generation rather than simply employing shadowing and visual functions. [7][8][9][10][11][12] Toward this purpose, ST-OSCs need to generate significant power while still maintaining good transparency and neutral-color perception, which can display a vivid picture when looking through ST-OSCs. [13,14] However, the current performance of ST-OSCs is much lower than their opaque counterparts due to their inherent trade-off between photocurrent and average visible transmittance (AVT) in the range of 380-780 nm. Even worse, these ST-OSCs generally display various colors, making it more difficult to realize high-performance ST-OSCs with promising AVT and neutral color simultaneously. To address the above issues, many efforts have been devoted to the following aspects: (1) developing high-conductivity and high-transparency electrodes to reduce the visible-light reflectance/absorption and contact resistance [15,16] ; (2) synthesizing a nonfullerene acceptor-based photoactive layer with low energy losses and strong near-infrared (NIR) absorption but weak visible absorption to simultaneously increase AVT and power conversion efficiency (PCE) [17][18][19][20][21] ; and (3) incorporating optical engineering to enhance absorption and tuning color conception. [22][23][24][25][26] Based on the above strategies, as shown in Figure 1a, ST-OSCs with promising PCEs of 8%-10% and AVT of over 20% were successfully constructed. [19,[27][28][29] However, the transmitted light still showed strong color bias because of the inhomogeneous device transmittance spectra.To achieve high color-fidelity ST-OSCs for building-integrated photovoltaics application, the light passing through ST-OSCs should maintain the initial component and relative intensity. In other words, the transmittance spectra with flattened, high-transparency, and horizontal characteristics in the visible region can enable neutral-color ST-OSCs. Generally, the color conception of ST-OSCs can be quantified by a color-rendering index (CRI) ranging from 0 to 100 and the color coordinates (x, y) on the Commission Internationale de L'Eclairage (CIE, in French) 1931 color space, where a high CRI value and color coordinates close to AM1.5G (0.35, 0.34) represent neutral-color ST-OSCs. [22,30] Colsmann and co-workers [31] added a red absorbing dye into a top transparent polymeric electrode to compensate for the missing Neutral-colored semitransparent organic solar cells (ST-OSCs) have attracted considerable attention owing to their unique application in no-visual-obstacle building-integrated photovoltaics. Toward this promising potential application, a synergistic effect is first proposed by employing a dielectric mirror and ternary photoactive layer with near-infrared absorption to tune the color perception as well as ST-OSC performance preci...

Solution processable flexible transparent electrodes (FTEs) are urgently needed to boost the efficiency and mechanical stability of flexible organic solar cells (OSCs) on a large scale. However, how to balance the optoelectronic properties and meanwhile achieve robust mechanical behavior of FTEs is still a huge challenge. Silver nanowire (AgNW) electrodes, exhibiting easily tuned optoelectronic/mechanical properties, are attracting considerable attention, but their poor contacts at the junction site of the AgNWs increase the sheet resistance and reduce mechanical stability. In this study, an ionic liquid (IL)-type reducing agent containing Cl − and a dihydroxyl group was employed to control the reduction process of silver (Ag) in AgNW-based FTEs precisely. The Cl − in the IL regulates the Ag + concentration through the formation and dissolution of AgCl, whereas the dihydroxyl group slowly reduces the released Ag + to form metal Ag. The reduced Ag grew in situ at the junction site of the AgNWs in a twin-crystal growth mode, facilitating an atomic-level contact between the AgNWs and the reduced Ag. This enforced atomic-level contact decreased the sheet resistance, and enhanced the mechanical stability of the FTEs. As a result, the single-junction flexible OSCs based on this chemically welded FTE achieved record power conversion efficiencies of 17.52% (active area: 0.062 cm 2 ) and 15.82% (active area: 1.0 cm 2 ). These flexible devices also displayed robust bending and peeling durability even under extreme test conditions.

Poly(vinyl alcohol) (PVOH)/clay aerogel composites were fabricated by an environmentally friendly freeze-drying of the aqueous precursor suspensions, followed by cross-linking induced by gamma irradiation without chemical additives. The influences of cross-linking conditions, i.e., absorbed dose and polymer loading as well as density on the aerogel structure and properties, were investigated. The absorbed dose of 30 kGy was found to be the optimum dose for fabricating strong PVOH composites; the compressive modulus of an aerogel prepared from an aqueous suspension containing 2 wt % PVOH/8 wt % clay increased 10-fold, and that containing 1 wt % PVOH/9 wt % clay increased 12 times upon cross-linking with a dose of 30 kGy. Increasing the solids concentration led to an increase in the mechanical strength, in accordance with the changes in microstructure from layered structure to network structure. The increase of absorbed dose also led to decreased porous size of the network structure. Cross-linking and the increase of the PVOH lead to decreased thermal stability. The strengthened PVOH/clay aerogels possess very low flammability, as measured by cone calorimetry, with heat, smoke, and volatile products release value decreasing as increasing clay content. The mechanism of flame retardation in these materials was investigated with weight loss, FTIR, WAXD, and SEM of the burned residues. The proposed mechanism is that with decreasing fuel content (increasing clay content), increased heat and mass transport barriers are developed; simultaneously low levels of thermal conductivity are maintained during the burning.

In this work, a new combination of a wide bandgap polymer poly[4,8‐bis(5‐(2‐ethylhexyl)thiophen‐2‐yl)benzo[1,2‐b:4,5‐b′]‐dithiophene‐alt‐N‐(2‐hexyldecyl)‐5′5‐bis[3‐(decylthio)thiophene‐2‐yl]‐2′2‐bithiophene‐3′3‐dicarboximide] (PBTIBDTT) and a non‐fullerene small molecule acceptor based on a bulky seven‐ring fused core (indacenodithieno[3,2‐b]thiophene) end‐capped with 2‐(3‐oxo‐2,3‐dihydroinden‐1‐ylidene)malononitrile groups with one fluorine substituent (ITIC‐F) is proposed, and as‐cast non‐fullerene organic solar cells (NFOSCs) with 11.2% efficiency are achieved. The device efficiencies are also insensitive to the variation of photoactive layer (PAL) thickness and can maintain over 9% efficiency as PAL thickness increases to 350 nm, which is one of the best results for as‐cast organic solar cells. More importantly, non‐fullerene organic photovoltaic (OPV) modules are demonstrated via laser ablation technique for the first time, which delivers a record efficiency of 8.6% (with active area of 3.48 cm2) among large‐area OPV modules. Furthermore, the morphology and performance evolutions of the as‐cast NFOSCs and the ones processed with solvent additive are systematically investigated. The results demonstrate the great advantage of as‐cast solar cells in achieving constant morphology and high performance with thick PALs. The NFOSCs fabricated with simple procedure, insensitive to film thickness and compatible with large‐area OPV modules, show significant potential for application the future.

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Two novel side-chain fluorinated n-SMAs were synthesized to study the effect of fluoro-side-chain engineering on the thermal stability of OSCs.