P3HT为空穴传输层的碳基钙钛矿太阳电池

碳电极具有成本低、印刷方便、可有效隔离水氧等优点,因此有望利用碳电极材料实现低成本、高稳定性的钙钛矿太阳电池。无空穴传输层的传统碳基钙钛矿太阳电池面临着空穴提取率低、电子逆向传输,钙钛矿和碳电极界面的载流子复合等问题。文章引入聚(3-己基噻吩)(P3HT)作为器件的空穴传输层,使碳基钙钛矿太阳电池ITO/SnO₂/MAPbI₃/P3HT/Carbon的光伏性能得到了显著改善:器件的光电转化效率从11.16% 提高到13.37%。在氮气环境下,连续光照1000h,太阳电池的光电转化效率可保持初始值的87%,而传统器件在光照500h后,其光电转化效率已下降至初始值的60%。     

Temperature‐Resolved Local and Macroscopic Charge Carrier Transport in Thin P3HT Layers

Previous investigations of the field‐effect mobility in poly(3‐hexylthiophene) (P3HT) layers revealed a strong dependence on molecular weight (MW), which was shown to be closely related to layer morphology. Here, charge carrier mobilities of two P3HT MW fractions (medium‐MW: M_n = 7 200 g mol^?1; high‐MW: M_n = 27 000 g mol^?1) are probed as a function of temperature at a local and a macroscopic length scale, using pulse‐radiolysis time‐resolved microwave conductivity (PR‐TRMC) and organic field‐effect transistor measurements, respectively. In contrast to the macroscopic transport properties, the local intra‐grain mobility depends only weakly on MW (being in the order of 10^?2 cm² V^?1 s^?1) and being thermally activated below the melting temperature for both fractions. The striking differences of charge transport at both length scales are related to the heterogeneity of the layer morphology. The quantitative analysis of temperature‐dependent UV/Vis absorption spectra according to a model of F. C. Spano reveals that a substantial amount of disordered material is present in these P3HT layers. Moreover, the analysis predicts that aggregates in medium‐MW P3HT undergo a “pre‐melting” significantly below the actual melting temperature. The results suggest that macroscopic charge transport in samples of short‐chain P3HT is strongly inhibited by the presence of disordered domains, while in high‐MW P3HT the low‐mobility disordered zones are bridged via inter‐crystalline molecular connections.     

The Impact of Polymer Regioregularity on Charge Transport and Efficiency of P3HT:PCBM Photovoltaic Devices

The charge transport in pristine poly(3‐hexylthiophene) (P3HT) films and in photovoltaic blends of P3HT with [6,6]‐phenyl C61 butyric acid methyl ester (PCBM) is investigated to study the influence of charge‐carrier transport on photovoltaic efficiency. The field‐ and temperature dependence of the charge‐carrier mobility in P3HT of three different regioregularities, namely, regiorandom, regioregular with medium regioregularity, and regioregular with very high regioregularity are investigated by the time‐of‐flight technique. While medium and very high regioregularity polymers show the typical absorption features of ordered lamellar structures of P3HT in the solid state even without previous annealing, films of regiorandom P3HT are very disordered as indicated by their broad and featureless absorption. This structural difference in the solid state coincides with partially non‐dispersive transport and hole mobilities µ_h of around 10^?4 and 10^?5 cm² V^?1 s^?1 for the high and medium regioregularity P3HT, respectively, and a slow and dispersive charge transport for the regiorandom P3HT. Upon blending the regioregular polymers with PCBM, the hole mobilities are typically reduced by one order of magnitude, but they do not significantly change upon additional post‐spincasting annealing. Only in the case of P3HT with high regioregularity are the electron mobilities similar to the hole mobilities and the charge transport is, thus, balanced. Nonetheless, devices prepared from both materials exhibit similar power conversion efficiencies of 2.5%, indicating that very high regioregularity may not substantially improve order and charge‐carrier transport in P3HT:PCBM and does not lead to significant improvements in the power‐conversion efficiency of photovoltaic devices.     

Morphological Origin of Charge Transport Anisotropy in Aligned Polythiophene Thin Films

The morphological origin of anisotropic charge transport in uniaxially strain aligned poly(3‐hexylthiophene) (P3HT) films is investigated. The macroscale field effect mobility anisotropy is measured in an organic thin film transistor (OTFT) configuration and compared to the local aggregate P3HT mobility anisotropy determined using time‐resolved microwave conductivity (TRMC) measurements. The field effect mobility anisotropy in highly aligned P3HT films is substantially higher than the local mobility anisotropy in the aggregate P3HT. This difference is attributed to preferentially aligned polymer tie‐chains at grain boundaries that contribute to macroscale charge transport anisotropy but not the local anisotropy. The formation of sharp grains between oriented crystalline P3HT, through tie chain removal by thermal annealing the strained aligned films, results in an order of magnitude drop in the measured field effect mobility for charge transport parallel to the strain direction. The field effect mobility anisotropy is cut in half while the local mobility anisotropy remains relatively constant. The local mobility anisotropy is found to be surprisingly low in the aligned films, suggesting that the π?π stacking direction supports charge carrier mobility on the same order of magnitude as that in the intrachain direction, possibly due to poor intrachain mobility through chain torsion.     

Coulomb Enhanced Charge Transport in Semicrystalline Polymer Semiconductors

Polymer semiconductors provide unique possibilities and flexibility in tailoring their optoelectronic properties to match specific application demands. The recent development of semicrystalline polymers with strongly improved charge transport properties forces a review of the current understanding of the charge transport mechanisms and how they relate to the polymer's chemical and structural properties. Here, the charge density dependence of field effect mobility in semicrystalline polymer semiconductors is studied. A simultaneous increase in mobility and its charge density dependence, directly correlated to the increase in average crystallite size of the polymer film, is observed. Further evidence from charge accumulation spectroscopy shows that charges accumulate in the crystalline regions of the polymer film and that the increase in crystallite size affects the average electronic orbitals delocalization. These results clearly point to an effect that is not caused by energetic disorder. It is instead shown that the inclusion of short range coulomb repulsion between charge carriers on nanoscale crystalline domains allows describing the observed mobility dependence in agreement with the structural and optical characterization. The conclusions that are extracted extend beyond pure transistor characterization and can provide new insights into charge carrier transport for regimes and timescales that are relevant to other optoelectronic devices.     

Controllable Molecular Doping and Charge Transport in Solution‐Processed Polymer Semiconducting Layers

Here, controlled p‐type doping of poly(2‐methoxy‐5‐(2′‐ethylhexyloxy)‐p‐phenylene vinylene) (MEH‐PPV) deposited from solution using tetrafluoro‐tetracyanoquinodimethane (F4‐TCNQ) as a dopant is presented. By using a co‐solvent, aggregation in solution can be prevented and doped films can be deposited. Upon doping the current–voltage characteristics of MEH‐PPV‐based hole‐only devices are increased by several orders of magnitude and a clear Ohmic behavior is observed at low bias. Taking the density dependence of the hole mobility into account the free hole concentration due to doping can be derived. It is found that a molar doping ratio of 1 F4‐TCNQ dopant per 600 repeat units of MEH‐PPV leads to a free carrier density of 4 × 10²² m^?3. Neglecting the density‐dependent mobility would lead to an overestimation of the free hole density by an order of magnitude. The free hole densities are further confirmed by impedance measurements on Schottky diodes based on F4‐TCNQ doped MEH‐PPV and a silver electrode.     

Graphene/Strontium Titanate: Approaching Single Crystal–Like Charge Transport in Polycrystalline Oxide Perovskite Nanocomposites through Grain Boundary Engineering

Grain boundaries critically limit the electronic performance of oxide perovskites. These interfaces lower the carrier mobilities of polycrystalline materials by several orders of magnitude compared to single crystals. Despite extensive effort, improving the mobility of polycrystalline materials (to meet the performance of single crystals) is still a severe challenge. In this work, the grain boundary effect is eliminated in perovskite strontium titanate (STO) by incorporating graphene into the polycrystalline microstructure. An effective mass model provides strong evidence that polycrystalline graphene/strontium titanate (G/STO) nanocomposites approach single crystal‐like charge transport. This phenomenological model reduces the complexity of analyzing charge transport properties so that a quantitative comparison can be made between the nanocomposites and STO single crystals. In other related works, graphene composites also optimize the thermal transport properties of thermoelectric materials. Therefore, decorating grain boundaries with graphene appears to be a robust strategy to achieve “phonon glass–electron crystal” behavior in oxide perovskites.     

Microstructural Control of Charge Transport in Organic Blend Thin‐Film Transistors

The charge‐transport processes in organic p‐channel transistors based on the small‐molecule 2,8‐difluoro‐5,11‐bis(triethylsilylethynyl)anthradithiophene (diF‐TES ADT), the polymer poly(triarylamine)(PTAA) and blends thereof are investigated. In the case of blend films, lateral conductive atomic force microscopy in combination with energy filtered transmission electron microscopy are used to study the evolution of charge transport as a function of blends composition, allowing direct correlation of the film's elemental composition and morphology with hole transport. Low‐temperature transport measurements reveal that optimized blend devices exhibit lower temperature dependence of hole mobility than pristine PTAA devices while also providing a narrower bandgap trap distribution than pristine diF‐TES ADT devices. These combined effects increase the mean hole mobility in optimized blends to 2.4 cm²/Vs – double the value measured for best diF‐TES ADT‐only devices. The bandgap trap distribution in transistors based on different diF‐TES ADT:PTAA blend ratios are compared and the act of blending these semiconductors is seen to reduce the trap distribution width yet increase the average trap energy compared to pristine diF‐TES ADT‐based devices. Our measurements suggest that an average trap energy of <75 meV and a trap distribution of <100 meV is needed to achieve optimum hole mobility in transistors based on diF‐TES ADT:PTAA blends.     

Effect of ZnSe quantum dot concentration on the fluorescence enhancement of polymer P3HT film

The effects of ZnSe quantum dot (Qd) concentration on the fluorescence in Poly(3-hexylthiophene-2,5-diyl) matrix (P3HT) are investigated. The fluorescence spectra were found to be very dependant on the Qd concentration and light emission is significantly enhanced by incorporation of ZnSe Qd in the polymer matrix. Using a theoretical model for hybrid (organic–inorganic) system, interesting numerical results for the light emission and relative quantum efficiency as a function of ZnSe Qd concentration were obtained. The theoretical results were found to be in good agreement with experimental data.     

Polymer Photovoltaic Cells Based on Solution‐Processable Graphene and P3HT

A soluble graphene, which has a one‐atom thickness and a two‐dimensional structure, is blended with poly(3‐hexylthiophene) (P3HT) and used as the active layer in bulk heterojunction (BHJ) polymer photovoltaic cells. Adding graphene to the P3HT induces a great quenching of the photoluminescence of the P3HT, indicating a strong electron/energy transfer from the P3HT to the graphene. In the photovoltaic devices with an ITO/PEDOT:PSS/P3HT:graphene/LiF/Al structure, the device efficiency increases first and then decreases with the increase in the graphene content. The device containing only 10 wt % of graphene shows the best performance with a power conversion efficiency of 1.1%, an open‐circuit voltage of 0.72 V, a short‐circuit current density of 4.0 mA cm⁻², and a fill factor of 0.38 under simulated AM1.5G conditions at 100 mW cm⁻² after an annealing treatment at 160 °C for 10 min. The annealing treatment at the appropriate temperature (160 °C, for example) greatly improves the device performance; however, an annealing at overgenerous conditions such as at 210 °C results in a decrease in the device efficiency (0.57%). The morphology investigation shows that better performance can be obtained with a moderate content of graphene, which keeps good dispersion and interconnection. The functionalized graphene, which is cheap, easily prepared, stable, and inert against the ambient conditions, is expected to be a competitive candidate for the acceptor material in organic photovoltaic applications.     

Mechanism of Crystallization and Implications for Charge Transport in Poly(3‐ethylhexylthiophene) Thin Films

In this work, crystallization kinetics and aggregate growth of poly(3‐ethylhexylthiophene) (P3EHT) thin films are studied as a function of film thickness. X‐ray diffraction and optical absorption show that individual aggregates and crystallites grow anisotropically and mostly along only two packing directions: the alkyl stacking and the polymer chain backbone direction. Further, it is also determined that crystallization kinetics is limited by the reorganization of polymer chains and depends strongly on the film thickness and average molecular weight. Time‐dependent, field‐effect hole mobilities in thin films reveal a percolation threshold for both low and high molecular weight P3EHT. Structural analysis reveals that charge percolation requires bridged aggregates separated by a distance of ≈2–3 nm, which is on the order of the polymer persistence length. These results thus highlight the importance of tie molecules and inter‐aggregate distance in supporting charge percolation in semiconducting polymer thin films. The study as a whole also demonstrates that P3EHT is an ideal model system for polythiophenes and should prove to be useful for future investigations into crystallization kinetics.     

Taming Charge Transport in Semiconducting Polymers with Branched Alkyl Side Chains

The solid‐state packing and polymer orientation relative to the substrate are key properties to control in order to achieve high charge carrier mobilities in organic field effect transistors (OFET). Intuitively, shorter side chains are expected to yield higher charge carrier mobilities because of a denser solid state packing motif and a higher ratio of charge transport moieties. However our findings suggest that the polymer chain orientation plays a crucial role in high‐performing diketopyrrolopyrrole‐based polymers. By synthesizing a series of DPP‐based polymers with different branched alkyl side chain lengths, it is shown that the polymer orientation depends on the branched alkyl chain lengths and that the highest carrier mobilities are obtained only if the polymer adopts a mixed face‐on/edge‐on orientation, which allows the formation of 3D carrier channels in an otherwise edge‐on‐oriented polymer chain network. Time‐of‐flight measurements performed on the various polymer films support this hypothesis by showing higher out‐of‐plane carrier mobilities for the partially face‐on‐oriented polymers. Additionally, a favorable morphology is mimicked by blending a face‐on polymer into an exclusively edge‐on oriented polymer, resulting in higher charge carrier mobilities and opening up a new avenue for the fabrication of high performing OFET devices.     

Nature of Charge Carriers in a High Electron Mobility Naphthalenediimide Based Semiconducting Copolymer

The nature of charge carriers in recently developed high mobility semiconducting donor‐acceptor polymers is debated. Here, localization due to charge relaxation is investigated in a prototypal system, a good electron transporting naphthalenediimide based copolymer, by means of current‐voltage I‐V electrical characteristics and charge modulation spectroscopy (CMS) in top‐gate field‐effect transistors (FETs), combined with density functional theory (DFT) and time dependent DFT (TDDFT) calculations. In particular, pristine copolymer films are compared with films that underwent a melt‐annealing process, the latter leading to a drastic change of the microstructure. Despite the packing modification, which involves also the channel region, both the electron mobility and the energy of polaronic transitions are substantially unchanged upon melt‐annealing. The polaron absorption features can be rationalized and reproduced by TDDFT calculations for isolated charged oligomers. Therefore, it is concluded that in such a high electron mobility copolymer the charge transport process involves polaronic species which are intramolecular in nature and, from a more general point of view, that interchain delocalization of the polaron is not necessary to sustain charge mobilities in the 0.1 to 1 cm² V^{– 1} s^–1 range. These findings contribute to the rationalization of the charge transport process in the recently developed class of donor‐acceptor π‐conjugated copolymers featuring high charge mobilities and complex morphologies.     

砷化镓声电荷转移延迟线的设计与工艺研究

由于声电荷转移(ACT)这一新颖的高速缓冲抽样技术的发明,使得新一代高速高频信号处理器件的实现成为可能。本文研究了第二代平面结构的ACT器件转移沟道的电位分布特性,给出了平面结构ACT延迟线的设计,并研究了ACT器件的工艺实现。     

基于电荷传输层优化的量子点发光二极管

采用溶液法旋涂薄膜、真空蒸镀铝电极,制备了ITO/PEDOT∶PSS/空穴传输材料/量子点/纳米氧化锌(ZnO Nanoparticles)/Al结构的量子点发光二极管(QLED)器件。对比了不同纳米氧化锌分散剂对器件性能的影响。当用乙醇和乙醇胺分散氧化锌时,对量子点层破坏较小,器件的亮度最高达22 940cd/m2,电流效率达28.9cd/A。研究了在聚乙烯咔唑(PVK)中掺杂不同比例4,4′-环己基二[N,N-二(4-甲基苯基)苯胺](TAPC)器件的发光特性。在PVK中掺杂TAPC材料能够促进器件空穴传输以及电子空穴注入平衡,当PVK∶TAPC=3∶1时,器件的空穴传输层形貌较为平整,亮度较高;当PVK∶TAPC=1∶1时,器件的开启电压最低。通过对器件膜层表面形貌以及电学、光学性能的对比,分析了电荷传输层优化对器件特性改善的原因。     

Highly Conductive Few‐Layer Graphene/Al2O3 Nanocomposites with Tunable Charge Carrier Type

An ex situ strategy for fabrication of graphene oxide (GO)/metal oxide hybrids without assistance of surfactant is introduced. Guided by this strategy, GO/Al₂O₃ hybrids are fabricated by two kinds of titration methods in which GO and Al₂O₃ colloids are utilized as titrant for hybrids of low and high GO content respectively. After sintered by spark plasma sintering, few‐layer graphene (FG)/Al₂O₃ nanocomposites are obtained and GO is well reduced to FG simultaneously. A percolation threshold as low as 0.38 vol.% is achieved and the electrical conductivity surpasses 10³ Sm^?1 when FG content is only 2.35 vol.% in FG/Al₂O₃ composite, revealing the homogeneous dispersion and high quality of as‐prepared FG. Furthermore, it is found that the charge carrier type changes from p‐ to n‐type as graphene content becomes higher. It is deduced that this conversion is related to the doping effect induced by Al₂O₃ matrix and is thickness‐dependent with respect to FG.     

Band-Like Charge Transport in Phytic Acid-Doped Polyaniline Thin Films

We explore the charge transport properties of phytic acid (PA) doped polyaniline thin films prepared by the surfactant monolayer-assisted interfacial synthesis (SMAIS). Structural and elemental analysis confirms the inclusion of PA in the thin films and reveals a progressive loss of crystallinity with the increase of PA doping content. Charge transport properties are interrogated by time-resolved terahertz (THz) spectroscopy. Notably, independently of doping content and hence crystallinity, the frequency-resolved complex conductivity spectra in the THz region can be properly described by the Drude model, demonstrating band-like charge transport in the samples and state-of-the-art charge carrier mobilities of ≈1 cm²V⁻¹s⁻¹. A temperature-dependent analysis for the conductivity further supports band-like charge transport and suggest that charge carrier mobility is primarily limited by impurity scattering. This work highlights the potential of PA doped polyaniline for organic electronics.     

Hole-injection enhancement of top-emissive polymer light-emitting diodes by P3HT/FNAB modification of Ag anode

Based on the hole-transport characteristic of poly(3-hexylthiophene) (P3HT), self-assembled thin layer of P3HT was employed to modify the Ag anode of a top-emissive polymer light-emitting diodes (T-PLEDs) to enhance the hole-injection from the Ag anode. The experimental results show that introduction of a P3HT thin layer significantly decreases the threshold voltage of a T-PLED. However, only slightly increase of the work function was achieved due to this modification. To increase the work function of the P3HT modified Ag anode (Ag/P3HT), 1-fluoro-2-nitro-4-azidobenzene (FNAB) was introduced into the terminal tail (–C₆H₁₃) of P3HT thin layer, which leads to a work function increment of 0.23 eV and a further enhancement in the hole-injection. The luminous efficiency achieved by this modified anode (Ag/P3HT/FNAB) is about fourfold higher than the efficiency obtained from the base device.