Recently, there are growing interests in ternary organic solar cells due to their expected broader absorption in comparison to their counterpart binary systems. It is found that open-circuit voltage in a ternary system can be largely tuned by varying the composition ratio of two donors or two acceptors integrated in. However, there is no detailed analysis for such an interesting observation. In this paper, we fabricated ternary solar cells with one p-type polymer as donor and two mixed n-type fullerenes as acceptor, and investigated the open-circuit voltage by varying the weight ratio of the two fullerenes. A three-diode model is developed to analyze the tunable behavior of open-circuit voltage displayed in our ternary system in terms of energy loss and dark current suppression. We also discussed the tunable open-circuit voltage based on electron and hole quasi-Fermi levels.

selection, [13,14] thermal annealing, [15,16] and solvent annealing. [13,17] In recent work, a variety of liquid additives, including 1,8-octanedithiol, [18] 1,8-diiodooctane (DIO), [19,20] nitrobenzene, [21] N-methylpyrrolidone, [22,23] chloronapthalene, [24] etc. have been introduced into the D/A blend. These additives successfully manipulated the nanomorphology of the active layer and markedly increased the efficiency of OSCs. Among these additives, DIO was the most used and also very effective one, power conversion efficiencies (PCEs) of over 10% have already been realized with the help of DIO in single-layer OSCs. [2][3][4][5][6][7][8] However, optimizing the ratio of additive in the parent solvent is a tedious process, and the additive also deteriorates the reproducibility of the device performance (PCE of the device is very sensitive to DIO ratio variation; the slow drying process of the residual high-boiling-point additive in the active layer could induce undesirable morphological change). [25] What's worse, residual DIO also greatly accelerates the photo-oxidative degradation by acting as a radial initiator and dramatically decreases the lifetime of the device. [26,27] To remove DIO in the film, several methods have been tried such as putting the film in high-vacuum environment, annealing the film at high temperature [26] and washing the film with methanol. [25] However, all these cannot root out the problem that DIO brings in: the high vacuum technique is not amenable to large scale manufacturing process, such as roll-to-roll. The high temperature annealing deteriorates the performance of most high-efficiency OSCs, such as PTB7-Th based ones, [28,29] and may be incompatible with the flexible substrates as well, such as poly(ethylene terephthalate). [30] Thereby, materials that can be processed with simple and reliable procedures which do not require additive addition and active layer post treatments (thermal annealing, solvent annealing, and surface modification) are urgently required. In this regard, several donor and acceptor materials have been tried. For example, Lin et al. employed a new acceptor ITIC-Th in fullerene-free solar cells and got a PCE of 7.5%, [31] Yue et al. designed a novel polymer donor TBTIT-h in OSCs and gained a PCE of 9.1%, [32] Zhang et al. applied a new polymer PBDT-TS1 in OSCs and realized a PCE of 9.67%. [33] In this paper, we utilized a D-A copolymer PThBDTP (consisting of a thiophene as the donor and BDTP as the acceptor unit), [34] and achieved a PCE of 10.06% based on the PThBDTP:PC 71 BM blend. As far as we know, such efficiency is the highest for those additive-free and post treatment free OSCs. Nowadays, solvent additives are widely used in organic solar cells (OSCs) to tune the nano-morphology of the active blend film and enhance the device performance. With their help, power conversion efficiencies (PCEs) of OSCs have recently stepped over 10%. However, residual additive in the device can induce undesirable morphological change and also accelerate photo-oxidation de...

Here, we put forward an effective strategy to regulate the interface structure of carbon nanotubes/polyaniline (CNTs/PANI) composite films and improve their thermoelectric (TE) properties by sequential dedoping-redoping treatment. Dedoping induces conductive resistance-undoped PANI to enhance the energy barrier between CNTs and PANI, leading to a greatly increased Seebeck coefficient and deteriorated conductivity. Subsequently, upon the redoping process, the electrical conductivity is dramatically improved owing to the generated conductive PANI chains, while Seebeck coefficient is maintained at 90% of the dedoped composites. This yields a significantly improved power factor of 407 μW m −1 K −2 from the as-prepared composites (234 μW m −1 K −2 ), which is the highest value among those of all the reported CNTs/ PANI composites. The outstanding TE performanceis probably ascribed to the multiple interface structure of the PANI composite generated from incomplete dedoping and redoping processes, contributing to the enhanced carrier-filtering effect to retain a relatively high Seebeck coefficient and efficient charge transport to improve conductivity. Furthermore, the flexible TE device generates a high power of 1.5 μW at ΔT = 50 K, demonstrating the applicability of this composite for energy-harvesting electronic devices.

No abstract

TiO 2 , as a benchmark in the field of ultraviolet photocatalysis, is one of the most widely used semiconductor photocatalysts. However, its inherent drawbacks, including wide bandgap and fast recombination of charge carriers, lead to the underutilization of solar light. Increasing the overall solar spectrum utilization of TiO 2 , especially in the near-infrared region (NIR, ≈52%), is the key to efficient solar energy conversion. In this review, the strategies to enhance NIR light capture of TiO 2 -based photocatalysts, including hybridization with narrow optical gap semiconductors, bandgap engineering, upconversion materials, plasmonic materials, and photosensitizers, are elaborated. The basic mechanisms for NIR light conversion employed by TiO 2 and the preparation methods of photoactive materials are summarized. Furthermore, their applications in photocatalytic pollutants purification, hydrogen and oxygen evolution, multifunctional smart windows, nitrogen photofixation, as well as carbon dioxide photoreduction and photocatalytic disinfection are discussed. Finally, this review presents the limitations and perspectives for the future development of efficient NIR solar photon conversion of TiO 2 -based materials.

Novel π-conjugated copolymers based on a soluble electroactive benzo[1,2-b:4,5-b 0 ]difuran (BDF) chromophore have been synthesized by the introduction of thiophene/benzo[c][1,2,5]thiadiazole/ 9-phenylcarbazole comonomer units. These copolymers cover broad absorption ranges from 250 to 700 nm with narrow optical band gaps of 1.71-2.01 eV. Moreover, their band gaps as well as their molecular electronic energy levels are readily tuned by copolymerizing the BDF core with different π-conjugated electron-donating or withdrawing units in different ratios. Bulk heterojunction solar cell devices are fabricated using the copolymers as the electron donor and PCBM ([6,6]-phenyl-C 61 -butyric acid methyl ester) as the electron acceptor. Preliminary research has revealed power conversion efficiencies of 0.17-0.59% under AM 1.5 illumination (100 mW/cm 2 ).

Interface engineering is an effective means to enhance the performance of thin‐film devices, such as perovskite solar cells (PSCs). Herein, a conjugated polyelectrolyte, poly[(9,9‐bis(3′‐((N,N‐dimethyl)‐N‐ethyl‐ammonium)‐propyl)‐2,7‐fluorene)‐alt‐2,7‐(9,9‐dioctylfluorene)]di‐iodide (PFN‐I), is used at the interfaces between the hole transport layer (HTL)/perovskite and perovskite/electron transport layer simultaneously, to enhance the device power conversion efficiency (PCE) and stability. The fabricated PSCs with an inverted planar heterojunction structure show improved open‐circuit voltage (Voc), short‐circuit current density (Jsc), and fill factor, resulting in PCEs up to 20.56%. The devices maintain over 80% of their initial PCEs after 800 h of exposure to a relative humidity 35–55% at room temperature. All of these improvements are attributed to the functional PFN‐I layers as they provide favorable interface contact and defect reduction.

One-step single-spinneret electrospinning synthesis of 1D fibrous hierarchical structure can not only prevent the agglomeration or restacking of fibers or particles and enlarge surface active area but also promote the directional migration of electrons in materials and achieve effective regulation of resistances. Herein, tunable SnO 2 and SnO 2 /ZnO fibrous hierarchical structures with in situ growth of monodisperse spherical-like particles on surface provide a new sight for adjusting component distribution, surface absorption and chemical reaction, electronic transmission path, and electron transfer efficiency. Compared with SnO 2 porous fibers and SnO 2 hierarchical structures, the optimal SnO 2 /ZnO sensors exhibit superior gas-sensing response value of 366−100 ppm ethanol at 260 °C as well as excellent gas selectivity and long-term stability, in which the enhanced gassensing mechanism is primarily derived from multilevel effective heterojunctions with unique interface electronic effects. Especially, these SnO 2 -based sensors can achieve favorable linear relationship of the response and gas concentration for sensitive trace detection in cosmetics for the first time, providing a new strategy to design composite materials for quantitative analysis of volatiles in the cosmetics evaluation process. KEYWORDS: SnO 2 and SnO 2 /ZnO fibrous hierarchical structures, multilevel effective heterojunctions, electrospinning, gas sensor, trace detection in cosmetics