PHOTOCONDUCTIVITY STUDY OF NEW POLYACETYLENE DERIVATIVES WITH DIFFERENT SUBSTITUENTS

The photoconductivities of a series of novel polyacetylene derivatives （PAs） serving as charge generation materials in the single-layered photoreceptors were investigated using photoinduced xerographic discharge technique. It was found that the substitution can improve the photosensitivity of PAs by increasing the conjugation of π electrons. When the substituent is itself photoconductive, the photoconductivity becomes even higher. It can be concluded from cyclic voltammetry that when the HOMO level of the polymer is closer to that of the charge transport material, the photoconduction performance will be better.

Non-fullerene Acceptors with a Thieno[3,4-c]pyrrole-4,6-dione(TPD) Core for Efficient Organic Solar Cells

To achieve the red-shifted absorptions and appropriate energy levels of A-D-A type non-fullerene acceptors(NFAs), in this work, we design and synthesize two new NFAs, named TPDCIC and TPDCNC, whose electron-donating(D) unit is constructed by a thieno[3,4-c]pyrrole-4,6-dione(TPD) core attached to two cyclopentadithiophene(CPDT) moieties at both sides, and the electronaccepting(A) end-groups are 2-(3-oxo-2,3-dihydroinden-1-ylidene)malononitrile(IC) and 2-(3-oxo-2,3-dihydro-1 H-cyclopenta[b]naphthalen-1-ylidene)malononitrile(NC), respectively. Benefiting from TPD core, which easily forms quinoid structure and O···H or O···S intramolecular noncovalent interactions, TPDCIC and TPDCNC show more delocalization of π-electrons and perfect planar molecular geometries, giving the absorption ranges extended to 822 and 852 nm, respectively. Furthermore, the highest occupied molecular orbital(HOMO) levels of TPDCIC and TPDCNC remain relatively low-lying due to the electronegativity of the carbonyl groups on TPD core. Considering that the absorptions and energy levels of the two NFAs match well with those of a widely used polymer donor, PBDB-T, we fabricate two kinds of organic solar cells(OSCs) based on the PBDB-T:TPDCIC and PBDB-T:TPDCNC blended films, respectively. Through a series of optimizations, the TPDCIC-based devices yield an impressing power conversion efficiency(PCE)of 10.12% with a large short-circuit current density(JSC) of 18.16 mA·cm-2, and the TPDCNC-based ones exhibit a comparable PCE of9.80% with a JSC of 17.40 mA·cm-2. Our work is the first report of the TPD-core-based A-D-A type NFAs, providing a good reference for the molecular design of high-performance NFAs.

Large-scale fabrication of field-effect transistors based on solution-grown organic single crystals

处理方法的一个简单答案被开发包括 6,13 二度(triisopropylsilylethynyl ) 种大规模排列得好的单个晶体 pentacene (TIPS-pentacene ) ，蒽， tetracene， perylene， C 60 和 tetracyanoquinodimethane。是由一根稳固的针卡住，半导体答案的微滴弄干进单个水晶的数组在上一 1 ? 厘米 ?瑡潩 n 飘 ? 飘？？

Solution-grown aligned crystals of diketopyrrolopyrroles(DPP)-based small molecules:Rough surfaces and relatively low charge mobility

Field-effect transistors（FETs） of three diketopyrrolopyrroles（DPP）-based small molecules, 3,6-bis（5-phenylthiophene-2-yl）-2,5-bis（2-ethylhexyl）pyrrolopyrrole-1,4-dione（PDPPP）, 3,6-bis（5-（4-fluorophenyl）thiophene-2-yl）-2,5-bis（2-ethylhexyl）pyrrolo pyrrole-1,4-dione（FPDPPPF） and 3,6-bis（5-（4-n-butylphenyl）thiophene-2-yl）-2,5-bis（2-ethylhexyl）pyrrolo pyrrole-1,4-dione（Bu PDPPPBu）, have been studied in this work. Well aligned crystals of the three molecules were grown from para-xylene by droplet-pinned crystallization method. FETs based on these aligned crystals exhibit a hole mobility up to0.19 cm^2 V 1s 1and electron mobility up to 0.008 cm^2 V 1s 1. The achieved hole mobility is of the same order of magnitude as reported highest hole mobility for DPP-based small molecules, but it is much lower than that of the high-performance DPP-based polymers. The relative low mobility is mainly attributed to the rough crystal surfaces with steps and, thus, non-smooth charge transport channels at the interfaces between the crystals and the dielectrics. This work has implications for understanding the low charge mobility of DPP-based small molecules.

Alignment and patterning of organic single crystals for field-effect transistors

Organic field-effect transistors are of great importance to electronic devices.With the emergence of various preparation techniques for organic semiconductor materials,the device performance has been improved remarkably.Among all of the organic materials,single crystals are potentially promising for high performances due to high purity and well-ordered molecular arrangement.Based on organic single crystals,alignment and patterning techniques are essential for practical industrial application of electronic devices.In this review,recently developed methods for crystal alignment and patterning are described.

Solution-processed CuOx as an efficient hole-extraction layer for inverted planar heterojunction perovskite solar cells

A solution-processed CuOx film has been successfully integrated as the hole-transporting layer（HTL） for inverted planar heterojunction perovskite solar cells（PVSCs）. The CuOx layer is fabricated by simply spin-coating a copper acetylacetonate（Cu（acac）2） chloroform solution onto ITO glass with high transparency in the visible range. The compact and pinhole-free perovskite film with large grain domains is grown on the CuOx film. The inverted PVSCs with the structure of ITO/CuOx/MAPbI3/PC（61）BM/ZnO/Al are fabricated and show a best PCE of 17.43% under standard AM 1.5G simulated solar irradiation with a VOCof 1.03 V, aJ（SC） of 22.42 mA cm^（-2）, and a fill factor of 0.76, which is significantly higher and more stable than that fabricated from the often used hole-transporting material PEDOT：PSS（11.98%） under the same experimental conditions. The enhanced performance is attributed to the efficient hole extraction through the CuOx layer as well as the high-quality CH3NH3PbI3 films grown on the CuOx. Our results indicate that low-cost and solution-processed CuOx film is a promising HTL for high performance PVSCs with better stability.

Gel-incorporated PbS and PbI_2 single-crystals

Gel-incorporated single-crystals provide unique combinational properties of long-range order and composite structures, which is desired for semiconducting and conducting materials. However, the reported gel-incorporated single-crystals are limited to insulating crystals. Here, we examine crystals of two typical semiconductors, lead sulfide （PbS） and lead iodide （Pbl2）, grown from both silica gels and agarose gels. In all the four crystal-gel pairs, single-crystals of the cubic phase of PbS and the hexagonal phase of Phi2 were obtained according to the X-ray diffraction analysis. Dissolution of the gel-grown crystals exposed insoluble materials with the shape similar to the original crystals, indicative of gelincorporation inside the crystals. As such, this work creates a facile strategy to construct 3D heterostructures inside serniconducting single-crystals without destroying their long-range order.

Shape change of calcite single crystals to accommodate interfacial curvature:Crystallization in presence of Mg2+ions and agarose gel-networks

Synthetic calcite single crystals,due to their strong crystal habit,tend to grow into characteristic rhombohedra.In the nature,biogenic calcite crystals form composites together with biomacromolecular materials,spurring investigations of how the growing calcite single crystals change their habit to satisfy the curvature of the organic phase.In this work,we examine calcite crystallization on a flat surface of glass slide and a curved surface of polystyrene（PS） sphere.The crystals exhibit tiny contact area onto the glass substrate that is averagely only 15%of their projected area on the substrate.In sharp contrast,the contact area greatly increase to above 75%of the projected area,once magnesium ions or agarose gel networks are introduced into the crystallization media.Furthermore,the calcite crystals form rough and step-like interfaces with a curved surface.However,the interfaces become smooth and curved as the crystals grow in presence of magnesium ions or agarose gel networks.The discrepancy between the interfacial structures implies kinetic effects of the additives on the crystallization around the surfaces.This work may provide implications for understanding the formation mechanisms of single-crystal composite materials.

Electron transport in solution-grown TIPS-pentacene single crystals:Effects of gate dielectrics and polar impurities

The n-channel behavior has been occasionally reported in the organic field-effect transistors （OFETs） that usually exhibit p-channel transport only. Reconfirmation and further examination of these unusual device performances should deepen the understanding on the electron transport in organic semiconductors. 6,13-bis（triisopropyl-silylethynyl） pentacene （TIPS-pentacene）, a widely examined p-channel material as Au is used for source-drain electrodes, has recently been reported to exhibit electron transport when grown from non-polar solvent on divinyltetramethyldisiloxanebis （benzocy- clobutene） （BCB） dielectric, spurring the study on this unusual electron transport. This paper describes FET characteristics of solution-grown TlPS-pentacene single crystals on five polymer gate dielectrics including polystyrene （PS）, poly（methyl methacrylate） （PMMA）, poly（4-vinyl phenol） （PVP）, poly（vinyl alcohol） （PVA） and poly（vinylidene fluoride-trifluoroethylene-chlorofluoroethylene） （P（VDF-TrFE-CFE））. In addition to the p-channel behavior, electron transport occurs in the crystals on PMMA, PS, thick PVA （40 nm） and a bilayer dielectric of PMMA on P（VDF-TrFE-CFE）, while does not on PVP and thin PVA （2 nm）. The two distinct FET characteristics are consistent with the previous reported trap effect of hydroxyl groups （in PVP and PVA） and reduced injection barrier by Na~ ions （as impurity in PVA）. The highest electron mobility of 0.48 cm2 V-1 s-1 has been achieved in the crystals on PMMA. Furthermore, the electron transport is greatly attenuated after the crystals are exposed to the vapor of a variety of polar solvents and the attenuated electron transport partially recovers if the crystals are heated, indicating the adverse effect of polar impurities on electron transport. By reconfirming the n-channel behavior in the OFETs based on TIPS-pentacene, this work has implications for the design of n-channel and ambipolar OFETs.

Unaxisymmetric Non-Fused Electron Acceptors for Efficient Polymer Solar Cells

To develop photovoltaics embracing the both features of high performance and low cost has drawn attentions of researchers,yet representing the significant challenges.In this work,two non-fused ring acceptors(NFRAs),namely p-PTIC4Cl and t-PTIC4Cl,were developed via a short synthetic route.By tethering unaxisymmetric aromatic chains to thienyl bridge of NFRAs,we revealed that the tuning of aromatic chains allows modulating the self-assembly and stacking of NFRAs in solid,hence influencing their optoelectronic and photovoltaic properties.As results,p-PTIC4Cl,consisting of 3-hexylbenzene with large axial angle to backbone,can achieve superior PCE of 11.30%than that of t-PTIC4Cl with 2-hexylthiophene chains(PCE of 6.49%),when pairing with polymer donor PBDB-TF.Despite of the only subtle structural difference,the p-PTIC4Cl based blend films possess better exciton dissociation and charge transfer rates,as well as photostability,to those of t-PTIC4Cl based blends.

Special Issue:Organic Photovoltaic Polymers

Organic photovoltaic devices(OPVs)show promise as the next-generation clean-energy technology with diverse applications,due to their unique merits of low-cost production with solution processability,light-weight,ultra-flexibility,good visible transparency for solar windows,aesthetic with vivid color,etc.Since the discovery of photovoltaic effect by sandwiching the Anthracene with electrodes,the OPVs has drawn more and more attention.In the most recent years,comprehensive research on materials design,interface modification,morphology control,device structure design,etc.,leads to the rapid progress in OPV.