Z Xin

Alternative low-temperature solution-processed hole-transporting materials (HTMs) without dopant are critical for highly efficient perovskite solar cells (PSCs). Here, two novel small molecule HTMs with linear π-conjugated structure, 4,4′-bis(4-(di-p-toyl)aminostyryl)biphenyl (TPASBP) and 1,4′-bis(4-(di-p-toyl)aminostyryl)benzene (TPASB), are applied as hole-transporting layer (HTL) by low-temperature (sub-100 °C) solution-processed method in p-i-n PSCs. Compared with standard poly(3,4-ethylenedioxythiophene): poly(styrenesulfonic acid) (PEDOT:PSS) HTL, both TPASBP and TPASB HTLs can promote the growth of perovskite (CH₃NH₃PbI₃) film consisting of large grains and less grain boundaries. Furthermore, the hole extraction at HTL/CH₃NH₃PbI₃ interface and the hole transport in HTL are also more efficient under the conditions of using TPASBP or TPASB as HTL. Hence, the photovoltaic performance of the PSCs is dramatically enhanced, leading to the high efficiencies of 17.4% and 17.6% for the PSCs using TPASBP and TPASB as HTL, respectively, which are ≈40% higher than that of the standard PSC using PEDOT:PSS HTL.

Two novel small molecular materials are explored as the hole-transporting layer in p-i-n perovskite solar cells (PSCs), yielding high efficiencies of 17.4% and 17.6%, respectively, which are ≈40% higher than the standard PSCs.

A nonfullerene polymer solar cell with a high efficiency of 9.26% is realized by using benzodithiophene–alt–fluorobenzotriazole copolymer J51 as a medium-bandgap polymer donor and the low-bandgap organic semiconductor ITIC with high extinction coefficients as the acceptor.

A novel non-fullerene acceptor, possessing a very low bandgap of 1.34 eV and a high-lying lowest unoccupied molecular orbital level of −3.95 eV, is designed and synthesized by introducing electron-donating alkoxy groups to the backbone of a conjugated small molecule. Impressive power conversion efficiencies of 8.4% and 10.7% are obtained for fabricated single and tandem polymer solar cells.

P(BDT-TCNT) and P(DTBDAT-TCNT), which has an extended conjugation length, were designed and synthesized for applications in organic solar cell (OSCs). The solution absorption maxima of P(DTBDAT-TCNT) with the extended conjugation were red-shifted by 5–15 nm compared with those of P(BDT-TCNT). The optical band gaps and highest occupied molecular orbital (HOMO) energy levels of both P(BDT-TCNT) and P(DTBDAT-TCNT) were similar. The structure properties of thin films of these materials were characterized using grazing-incidence wide-angle X-ray scattering and tapping-mode atomic force microscopy, and charge carrier mobilities were characterized using the space-charge limited current method. OSCs were formed using [6,6]-phenyl-C₇₁-butyric acid methyl ester (PC₇₁BM) as the electron acceptor and 3% diphenylether as additive suppress aggregation. OSCs with P(BDT-TCNT) as the electron donor exhibited a power conversion efficiency (PCE) of 4.10% with a short-circuit current density of J_SC = 9.06 mA/cm², an open-circuit voltage of V_OC = 0.77 V, and a fill factor of FF = 0.58. OSCs formed using P(DTBDAT-TCNT) as the electron donor layer exhibited a PCE of 5.83% with J_SC = 12.2 mA/cm², V_OC = 0.77 V, and FF = 0.62. © 2016 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2016, 54, 3182–3192

Newly designed and synthesized P(BDT-TCNT) and P(DTBDAT-TCNT) materials were discussed, the latter of which exhibits an extended conjugation length, for application in OSCs. The optical band gaps and HOMO energy levels were similar, OSCs formed with P(BDT-TCNT) exhibited a PCE of 4.10% with J_SC = 9.06 mA/cm², with V_OC = 0.77 V, and FF = 0.58. OSCs formed using P(DTBDAT-TCNT) exhibited a PCE of 5.83% with J_SC = 12.2 mA/cm², V_OC = 0.77 V, and FF = 0.62. The improved performance of the P(DTBDAT-TCNT)-based devices may be explained by considering the larger current due to shorter inter-lamella interaction, as a more balanced ratio μ_hole/μ_electron, resulting from extended conjugation of P(DTBDAT-TCNT).

Three acceptor–acceptor (A–A) type conjugated polymers based on isoindigo and naphthalene diimide/perylene diimide are designed and synthesized to study the effects of building blocks and alkyl chains on the polymer properties and performance of all-polymer photoresponse devices. Variation of the building blocks and alkyl chains can influence the thermal, optical, and electrochemical properties of the polymers, as indicated by thermogravimetric analysis, differential scanning calorimetry, UV–vis, cyclic voltammetry, and density functional theory calculations. Based on the A–A type conjugated polymers, the most efficient all-polymer photovoltaic cells are achieved with an efficiency of 2.68%, and the first all-polymer photodetectors are constructed with high responsivity (0.12 A W⁻¹) and detectivity (1.2 × 10¹² Jones), comparable to those of the best fullerene based organic photodetectors and inorganic photodetectors. Photoluminescence spectra, charge transport properties, and morphology of blend films are investigated to elucidate the influence of polymeric structures on device performances. This contribution demonstrates a strategy of systematically tuning the polymeric structures to achieve high performance all-polymer photoresponse devices.

Three n-type conjugated polymers are synthesized to achieve the most efficient acceptor–acceptor type polymer-based all-polymer photovoltaic cells with an efficiency of 2.68% and the first all-polymer photodetectors with high responsivity (0.12 A W⁻¹) and detectivity (1.2 × 10¹² Jones). This contribution provides a strategy of tuning the polymeric structures to achieve high performance all-polymer photoresponse devices.

Despite the emergence of direct arylation polymerization (DArP) as an alternative method to traditional cross-coupling routes like Stille polymerization, the exploration of DArP polymers in practical applications like polymer solar cells (PSCs) is limited. DArP polymers tend to have a reputation for being marginally inferior to Stille counterparts due to the increased presence of defects that result from unwanted side reactions in direct arylation, such as unselective C-H bond activation and homocoupling. We report ten DArP protocols across the three major classes of DArP to generate poly[(2,5-bis(2-hexyldecyloxy)phenylene)-alt-(4,7-di(thiophen-2-yl)benzo[c][1,2,5]thiadiazole)] (PPDTBT). Through evaluation of the method and resulting photophysical and electronic properties, we show not all DArP methods are suitable for generating device-quality alternating copolymers. When DArP PPDTBT was synthesized in superheated THF with Cs₂CO₃, neodecanoic acid, and P(o-anisyl)₃, it generated polymers of exceptional quality that performed comparably to Stille counterparts in both roll coated ITO-free and spin-coated ITO devices. © 2016 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2016, 54, 2907–2918

An effective OPV model compound, PPDTBT, has been utilized as a model system for the evaluation of ten DArP protocols derived from several classes of DArP on the OPV compatibility of DArP. The structural integrity of DArP PPDTBT has been investigated and compared with Stille counterparts. Flexible ITO-free and rigid ITO PSCs were prepared, showing—with precise reaction conditions—DArP can be a polymerization technique suitable for organic photovoltaics.

This study has proposed to use a well-defined oligomer F4TBT4 to replace its analogue polymer as electron acceptor toward tuning the phase separation behavior and enhancing the photovoltaic performance of all-polymer solar cells. It has been disclosed that the oligomer acceptor favors to construct pure and large-scale phase separation in the polymer:oligomer blend film in contrast to the polymer:polymer blend film. This gets benefit from the well-defined structure and short rigid conformation of the oligomer that endows it aggregation capability and avoids possible entanglement with the polymer donor chains. The charge recombination is to some extent suppressed and charge extraction is also improved. Finally, the P3HT:F4TBT4 solar cells not only output a high V_OC above 1.2 V, but also achieve a power conversion efficiency of 4.12%, which is two times higher than the P3HT:PFTBT solar cells and is comparable to the P3HT:PCBM solar cells. The strategy of constructing optimum phase separation with oligomer to replace polymer opens up new prospect for the further improvement of the all-polymer solar cells.

A well-defined oligomer F4TBT4 is proposed to replace its polymer PFTBT as electron acceptor to fabricate fullerene-free polymer solar cells. The oligomer acceptor favors to construct pure and large-scale phase separation in polymer blend film due to decreased chain entanglement. The resulted P3HT:F4TBT4 solar cells not only output a high V_OC above 1.2 V, but also achieve a PCE of 4.12%.

The structural and electronic properties of four isomers of didodecyl[1]-benzothieno[3,2-b][1]benzothiophene (C12-BTBT) have been investigated. Results show the strong impact of the molecular packing on charge carrier transport and electronic polarization properties. Field-induced time-resolved microwave conductivity measurements unravel an unprecedented high average interfacial mobility of 170 cm² V⁻¹ s⁻¹ for the 2,7-isomer, holding great promise for the field of organic electronics.

Many high charge carrier mobility (μ) active layers within organic field-effect transistor (OFET) configurations exhibit non-linear current–voltage characteristics that may drift with time under applied bias and, when applying conventional equations for ideal FETs, may give inconsistent μ values. This study demonstrates that the introduction of electron deficient fullerene acceptors into thin films comprised of the high-mobility semiconducting polymer PCDTPT suppresses an undesirable “double-slope” in the current–voltage characteristics, improves operational stability, and changes ambipolar transport to unipolar transport. Examination of other high μ polymers shows general applicability. This study also shows that one can further reduce instability by tuning the relative electron affinity of the polymer and fullerene by creating blends containing different fullerene derivatives and semiconductor polymers. One can obtain hole μ values up to 5.6 cm² V^–1 s^–1 that are remarkably stable over multiple bias-sweeping cycles. The results provide a simple, solution-processable route to dictate transport properties and improve semiconductor durability in systems that display similar non-idealities.

By using fullerene derivatives as additives in ambipolar polymer semiconductor field-effect transistors, the suppression of an undesirable double-slope in the I_d^1/2 versus V_g plots, improved I_ON/I_OFF, and stable V_T and hole μ through bias stress are observed. These findings also provide a convenient route to fabricate p-type organic field-effect transistors from ambipolar semiconductors.

A three-color warm-white organic light-emitting diode employing an efficient phosphor–phosphor type host–guest emitting system achieves efficiencies of 27.3% for external quantum efficiency and 74.5 lm W^–1 for power efficiency at a luminance of 1000 cd m^–2, which maintained the high levels of 24.3% and 45.8 lm W⁻¹ at 10 000 cd m⁻², with a stable color-rendering index of 86–87.

Solution-processed n-channel organic thin-film transistors (OTFTs) that exhibit a field-effect mobility as high as 11 cm² V⁻¹ s⁻¹ at room temperature and a band-like temperature dependence of electron mobility are reported. By comparison of solution-processed OTFTs with vacuum-deposited OTFTs of the same organic semiconductor, it is found that grain boundaries are a key factor inhibiting band-like charge transport.

Using a single emitter of Cu−Ga−S/ZnS quantum dots, all-solution-processed white electroluminescent lighting device that not only exhibits the record quantities of 1007 cd m⁻² in luminance and 1.9% in external quantum efficiency but also possesses satisfactorily high color rendering indices of 83−88 is demonstrated.

Highly efficient polymer solar cells with tandem structure are fabricated by using two excellent photovoltaic polymers and a highly transparent intermediate recombination layer. Power conversion efficiencies over 11% can be realized featured by a low-band-gap polymer with fine-tuned properties.

Blue-phosphorescent organic light-emitting diodes (OLEDs) with 34.1% external quantum efficiency (EQE) and 79.6 lm W⁻¹ are demonstrated using a hole-transporting layer and electron-transporting layer with low refractive index values. Using optical simulations, it is predicted that outcoupling efficiencies with EQEs > 60% can be achieved if organic layers with a refractive index of 1.5 are used for OLEDs.

Organic dyes and pigments constitute a large class of industrial products. The utilization of these compounds in the field of organic electronics is reviewed with particular emphasis on organic field-effect transistors. It is shown that for most major classes of industrial dyes and pigments, i.e., phthalocyanines, perylene and naphthalene diimides, diketopyrrolopyrroles, indigos and isoindigos, squaraines, and merocyanines, charge-carrier mobilities exceeding 1 cm² V⁻¹ s⁻¹ have been achieved. The most widely investigated molecules due to their n-channel operation are perylene and naphthalene diimides, for which even values close to 10 cm² V⁻¹ s⁻¹ have been demonstrated. The fact that all of these π-conjugated colorants contain polar substituents leading to strongly quadrupolar or even dipolar molecules suggests that indeed a much larger structural space shows promise for the design of organic semiconductor molecules than was considered in this field traditionally. In particular, because many of these dye and pigment chromophores demonstrate excellent thermal and (photo-)chemical stability in their original applications in dyeing and printing, and are accessible by straightforward synthetic protocols, they bear a particularly high potential for commercial applications in the area of organic electronics.

Many π-scaffolds derived from organic colorants exhibit excellent properties in organic thin-film transistors, single-crystal transistors, and organic solar cells. These results are remarkable because most of these molecules are quadrupolar or even dipolar, and accordingly do not comply with conventional design principles for organic semiconductors.