A highly flexible and transparent conductive electrode based on consecutively stacked layers of conductive polymer (CP) and silver nanowires (AgNWs) fully embedded in a colorless polyimide (cPI) is achieved by utilizing an inverted layer‐by‐layer processing method. This CP‐AgNW composite electrode exhibits a high transparency of >92% at wavelengths of 450–700 nm and a low resistivity of 7.7 Ω ◻−1, while its ultrasmooth surface provides a large contact area for conductive pathways. Furthermore, it demonstrates an unprecedentedly high flexibility and good mechanical durability during both outward and inward bending to a radius of 40 μm. Subsequent application of this composite electrode in organic solar cells achieves power conversion efficiencies as high as 7.42%, which represents a significant improvement over simply embedding AgNWs in cPI. This is attributed to a reduction in bimolecular recombination and an increased charge collection efficiency, resulting in performance comparable to that of indium tin oxide‐based devices. More importantly, the high mechanical stability means that only a very slight reduction in efficiency is observed with bending (<5%) to a radius of 40 μm. This newly developed composite electrode is therefore expected to be directly applicable to a wide range of high‐performance, low‐cost flexible electronic devices.

Thiourea was used as an additive in the iodide/iodine redox electrolyte for dye-sensitized solar cell and its effect was investigated. Thiourea was found to have the simultaneous effect of a positive band edge shift and a decrease in charge recombination rate. Addition of 0.05 M thiourea in the electrolyte comprising 0.7 M 1-methyl-3-propylimidazolium iodide (MPII) and 0.05 M I2 in acetonitrile enhanced significantly photocurrent density from 7.7 to 10.8 mA/cm2, while voltage decreased from 0.78 to 0.71 V. As a result, overall conversion efficiency increased from 4.7% to 5.8%, corresponding to increment of 23%. The solution acidity was changed from pK a = 18.9 (thiourea in acetonitrile) to pK a = 4.9 (thiourea in iodide- and iodine-containing acetonitrile), corresponding to change in pH from 10.1 to 3.1, which was attributed to chemical reaction between thiourea and iodine. As a consequence of the reaction, protons were produced and triiodide concentration was slightly reduced. The generation of protons in the electrolyte, associated with a positive shift of conduction band edge, led to a significant increase in photocurrent density. The unexpectedly small voltage drop, however, was ascribed to a slow recombination rate due to the reduced triiodide concentration. A large increase in photocurrent density along with a small decrease in voltage was also demonstrated from the variation of thiourea concentration.

A new series of liquid crystal embedded in polymeric electrolytes was developed for obtaining high efficiency in quasi‐solid state dye‐sensitized solar cells (DSSCs). The polymeric electrolytes were composed of iodide and tri‐iodide redox species in polyacrylonitrile (PAN) as a polymer matrix and liquid crystals (E7 or ML‐0249) for increasing the order parameter of electrolyte components with easy transport of redox species. The highest efficiency (6.21 and 6.29% at 1 sun) was obtained for the quasi‐solid state DSSCs using E7 to PAN and ML‐0249 to PAN, respectively, under AM 1.5 G illumination and an aperture mask condition. The high efficiencies of the quasi‐solid state DSSCs are due to the effective formation of pathways through liquid crystal orientation for the transport of redox species.magnified image

We synthesized a series of push−pull-type copolymers by copolymerizing an electron-deficient diketopyrrolopyrrole with three electron-donating benzodithiophene (BDT) moieties. PDPPDTT, which incorporated a dithienothiophene (DTT), showed a higher power conversion efficiency (PCE) of 6.11% compared to 3.31% for the BDTbased polymer (PDPPBDT). PDPPDTBDT, which incorporated a dithienobenzodithiophene (DTBDT), also exhibited superior performance, with a PCE of 4.75% although this value was lower than that obtained for PDPPDTT. The presence of the DTT unit in the polymer backbone lowered the energy bandgap of the polymer and induced an optimal morphology in the polymer:PC 71 BM blend film, resulting in higher charge carrier generation. Furthermore, the effectively delocalized frontier orbitals of PDPPDTT enhanced intermolecular interactions between the polymer chains by favoring effective π−π stacking, which facilitated charge carrier transport. By contrast, PDPPDTBDT unexpectedly showed a low-crystallinity thin film despite its backbone planarity, which reduced the performance relative to that of PDPPDTT. Importantly, PDPPDTT exhibited significantly better device stability compared to the other polymers in a light soaking test due to the much higher photochemical stability of PDPPDTT. We demonstrated a systematic approach to simultaneously increasing the photovoltaic performances and device stability, and we explored the basis for the structure−property relationship that accompanied such improvements. ■ INTRODUCTIONOver the past decade, bulk heterojunction polymer solar cells (BHJ PSCs) prepared using conjugated polymers as an electron donor and fullerene derivatives (e.g., [6,6]-phenyl C 71 -butyric acid methyl ester, PC 71 BM) as an electron acceptor have been extensively studied, 1 and power conversion efficiencies (PCEs) have reached values of ∼9% for single cells 2 and ∼10% for tandem cells. 3 A lot of conjugated polymers have been developed to achieve high photovoltaic properties, and design strategies relevant to organic photovoltaic devices to achieve a high PCE in BHJ solar cells have been set. Further advancements in the efficiency of a PSC will require developments of new conjugated polymers that satisfy several important criteria, including 4,5 (i) efficient light harvesting to increase the short-circuit current (J sc ), (ii) a lowest unoccupied molecular orbital (LUMO) energy level in the polymer should be at least 0.3 eV higher than that of the acceptor to provide a driving force for efficient charge separation at the polymer/ acceptor interface, (iii) energy offsets between the highest occupied molecular orbital (HOMO) level of the conjugated polymer and the LUMO level of the fullerene derivative should be sufficient to support a high open-circuit voltage (V oc ), (iv) morphology in the BHJ polymer blend should be optimal and include a nanoscale interpenetrating network to achieve a high interfacial area and efficient charge separation and transport, and (v) charge carrier mobilities should be high to ...

The three different methods of click reaction has been used to synthesize fluorene‐based click polymers and compared its effect on polymer electro‐optical properties as well as photovoltaic performances in DSSCs. The DSSCs devices with configuration of SnO2:F/TiO2/N719 dye/quasi‐solid‐state electrolyte/Pt devices were fabricated using these click polymers as a quasi‐solid‐state electrolyte components. Among the devices, the catalyzed click polymer composed DSSCs device exhibited high power conversion efficiency (PCE) of 4.62% under AM 1.5G illumination. These click polymers are promising materials for device application and the CuI‐catalyst 1,3‐dipolar cycloaddition click reaction is an efficient synthetic methodology.magnified image