High Tg Cyclic Olefin Copolymer Gate Dielectrics for N,N′‐Ditridecyl Perylene Diimide Based Field‐Effect Transistors: Improving Performance and Stability with Thermal Treatment

A novel application of ethylene‐norbornene cyclic olefin copolymers (COC) as gate dielectric layers in organic field‐effect transistors (OFETs) that require thermal annealing as a strategy for improving the OFET performance and stability is reported. The thermally‐treated N,N′‐ditridecyl perylene diimide (PTCDI‐C13)‐based n‐type FETs using a COC/SiO₂ gate dielectric show remarkably enhanced atmospheric performance and stability. The COC gate dielectric layer displays a hydrophobic surface (water contact angle = 95° ± 1°) and high thermal stability (glass transition temperature = 181 °C) without producing crosslinking. After thermal annealing, the crystallinity improves and the grain size of PTCDI‐C13 domains grown on the COC/SiO₂ gate dielectric increases significantly. The resulting n‐type FETs exhibit high atmospheric field‐effect mobilities, up to 0.90 cm² V^?1 s^?1 in the 20 V saturation regime and long‐term stability with respect to H₂O/O₂ degradation, hysteresis, or sweep‐stress over 110 days. By integrating the n‐type FETs with p‐type pentacene‐based FETs in a single device, high performance organic complementary inverters that exhibit high gain (exceeding 45 in ambient air) are realized.     

Organic Electronics: High Tg Cyclic Olefin Copolymer Gate Dielectrics for N,N′‐Ditridecyl Perylene Diimide Based Field‐Effect Transistors: Improving Performance and Stability with Thermal Treatment (Adv. Funct. Mater. 16/2010)

A novel application of ethylene‐norbornene cyclic olefin copolymers (COC) as gate dielectric layers in organic field‐effect transistors (OFETs) that require thermal annealing as a strategy for improving the OFET performance and stability is reported. The thermally‐treated N,N′‐ditridecyl perylene diimide (PTCDI‐C13)‐based n‐type FETs using a COC/SiO₂ gate dielectric show remarkably enhanced atmospheric performance and stability. The COC gate dielectric layer displays a hydrophobic surface (water contact angle = 95° ± 1°) and high thermal stability (glass transition temperature = 181 °C) without producing crosslinking. After thermal annealing, the crystallinity improves and the grain size of PTCDI‐C13 domains grown on the COC/SiO₂ gate dielectric increases significantly. The resulting n‐type FETs exhibit high atmospheric field‐effect mobilities, up to 0.90 cm² V^?1 s^?1 in the 20 V saturation regime and long‐term stability with respect to H₂O/O₂ degradation, hysteresis, or sweep‐stress over 110 days. By integrating the n‐type FETs with p‐type pentacene‐based FETs in a single device, high performance organic complementary inverters that exhibit high gain (exceeding 45 in ambient air) are realized.     

Measuring Domain Sizes and Compositional Heterogeneities in P3HT‐PCBM Bulk Heterojunction Thin Films with 1H Spin Diffusion NMR Spectroscopy

The application of ¹H spin diffusion nuclear magnetic resonance (NMR) is expanded to polymer‐fullerene blends for bulk heterojunction (BHJ) organic photovoltaics (OPV) by developing a new experimental methodology for measuring the thin films used in poly‐3‐hexylthiophene–phenyl C61‐butyric acid methyl ester (P3HT‐PCBM) OPV devices and by creating an analysis framework for estimating domain size distributions. It is shown that variations in common P3HT‐PCBM BHJ processing parameters such as spin‐coating speed and thermal annealing can significantly affect domain size distributions, which in turn affect power conversion efficiency. ¹H spin diffusion NMR analysis reveals that films spin‐cast at fast speeds in dichlorobenzene are primarily composed of small (<10 nm) domains of each component; these devices exhibit low power conversion efficiencies (η = 0.4%). Fast‐cast films improve substantially by thermal annealing, which causes nanometer‐scale coarsening leading to higher efficiency (η = 2.2%). Films spin‐cast at slow speeds and then slowly dried exhibit larger domains and even higher efficiencies (η = 2.6%), but do not benefit from thermal annealing. The ¹H spin diffusion NMR results show that a significant population of domains tens of nanometers in size is a common characteristic of samples with higher efficiencies.     

Correlating Emissive Non‐Geminate Charge Recombination with Photocurrent Generation Efficiency in Polymer/Perylene Diimide Organic Photovoltaic Blend Films

Evidence for a correlation between the dynamics of emissive non‐geminate charge recombination within organic photovoltaic (OPV) blend films and the photocurrent generation efficiency of the corresponding blend‐based solar cells is presented. Two model OPV systems that consist of binary blends of electron acceptor N′‐bis(1‐ethylpropyl)‐3,4,9,10‐perylene tetracarboxy diimide (PDI) with either poly(9,9‐dioctylfluorene‐co‐benzothiadiazole) (F8BT) or poly(9,9‐dioctylindenofluorene‐co‐benzothiadiazole) (PIF8BT) as electron donor are studied. For the F8BT:PDI and PIF8BT:PDI devices photocurrent generation efficiency is shown to be related to the PDI crystallinity. In contrast to the F8BT:PDI system, thermal annealing of the PIF8BT:PDI layer at 90 °C has a positive impact on the photocurrent generation efficiency and yields a corresponding increase in PL quenching. The devices of both blends have a strongly reduced photocurrent on higher temperature annealing at 120 °C. Delayed luminescence spectroscopy suggests that the improved efficiency of photocurrent generation for the 90 °C annealed PIF8BT:PDI layer is a result of optimized transport of the photogenerated charge‐carriers as well as of enhanced PL quenching due to the maintenance of optimized polymer/PDI interfaces. The studies propose that charge transport in the blend films can be indirectly monitored from the recombination dynamics of free carriers that cause the delayed luminescence. For the F8BT:PDI and PIF8BT:PDI blend films these dynamics are best described by a power‐law decay function and are found to be temperature dependent.     

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.     

Effects of Thermal Annealing Upon the Morphology of Polymer–Fullerene Blends

Grazing incidence X‐ray scattering (GIXS) is used to characterize the morphology of poly(3‐hexylthiophene) (P3HT)–phenyl‐C61‐butyric acid methyl ester (PCBM) thin film bulk heterojunction (BHJ) blends as a function of thermal annealing temperature, from room temperature to 220 °C. A custom‐built heating chamber for in situ GIXS studies allows for the morphological characterization of thin films at elevated temperatures. Films annealed with a thermal gradient allow for the rapid investigation of the morphology over a range of temperatures that corroborate the results of the in situ experiments. Using these techniques the following are observed: the melting points of each component; an increase in the P3HT coherence length with annealing below the P3HT melting temperature; the formation of well‐oriented P3HT crystallites with the (100) plane parallel to the substrate, when cooled from the melt; and the cold crystallization of PCBM associated with the PCBM glass transition temperature. The incorporation of these materials into BHJ blends affects the nature of these transitions as a function of blend ratio. These results provide a deeper understanding of the physics of how thermal annealing affects the morphology of polymer–fullerene BHJ blends and provides tools to manipulate the blend morphology in order to develop high‐performance organic solar cell devices.     

Evolution of Structure,Optoelectronic Properties,and Device Performance of Polythiophene:Fullerene Solar Cells During Thermal Annealing

We use spectroscopic ellipsometry to study the evolution of structure and optoelectronic properties of poly(3‐hexylthiophene) (P3HT) and [6,6]‐phenyl C61‐butyric acid methyl ester (PCBM) photovoltaic thin film blends upon thermal annealing. Four distinct processes are identified: the evaporation of residual solvent above the glass transition temperature of the blend, the relaxation of non‐equilibrium molecular conformation formed through spin‐casting, the crystallization of both P3HT and PCBM components, and the phase separation of the P3HT and PCBM domains. Devices annealed at 150 °C for between 10 and 60 min exhibit an average power conversion efficiency of around 4.0%. We find that the rate at which the P3HT/PCBM is returned to room temperature is more important in determining device efficiency than the duration of the isothermal annealing process. We conclude that the rapid quenching of a film from the annealing temperature to room temperature hampers the crystallization of the P3HT and can trap non‐equilibrium morphological states. Such states apparently impact on device short circuit current, fill factor and, thus, operational efficiency.     

Tuning the Morphology and Performance of Low Bandgap Polymer:Fullerene Heterojunctions via Solvent Annealing in Selective Solvents

Low bandgap polymer (LBG):fullerene mixtures are some of the most promising organic photovoltaic active layers. Unfortunately, there are no post‐deposition treatments available to rationally improve the morphology and performance of as‐cast LBG:fullerene OPV active layers, where thermal annealing usually fails. Therefore, there is a glaring need to develop post‐deposition methods to guide the morphology of LBG:fullerene bulk heterojunctions towards targeted structures and performance. In this paper, the structural evolution of PCPDTBT:PCBM mixtures with solvent annealing (SA) is examined, focusing on the effect of solvent quality of the fullerene and polymer in the annealing vapor on morphological evolution and device performance. The results indicate that exposure of this active layer to the solvent vapor controls the ordering of PCPDTBT and PCBM phase separation very effectively, presumably by inducing component mobility as the solvent plasticizes the mixture. These results also unexpectedly indicate that solvent annealing in a selective solvent provides a method to invert the morphology of the LBG:fullerene mixture from a polymer aggregate dispersed in a polymer:fullerene matrix to fullerene aggregates dispersed in a polymer:fullerene matrix. The judicious choice of solvent vapor, therefore, provides a unique method to exquisitely control and optimize the morphology of LBG conjugated polymer/fullerene mixtures.     

Single Component Organic Solar Cells Based on Oligothiophene‐Fullerene Conjugate

A new donor (D)–acceptor (A) conjugate, benzodithiophene‐rhodanine–[6,6]‐phenyl‐C₆₁ butyric acid methyl ester (BDTRh–PCBM) comprising three covalently linked blocks, one of p‐type oligothiophene containing BDTRh moieties and two of n‐type PCBM, is designed and synthesized. A single component organic solar cell (SCOSC) fabricated from BDTRh–PCBM exhibits the power conversion efficiency (PCE) of 2.44% and maximum external quantum efficiency of 46%, which are the highest among the reported efficiencies so far. The SCOSC device shows efficient charge transfer (CT, ≈300 fs) and smaller CT energy loss, resulting in the higher open‐circuit voltage of 0.97 V, compared to the binary blend (BDTRh:PCBM). Because of the integration of the donor and acceptor in a single molecule, BDTRh‐PCBM has a specific D–A arrangement with less energetic disorder and reorganization energy than blend systems. In addition, the SCOSC device shows excellent device and morphological stabilities, showing no degradation of PCE at 80 °C for 100 h. The SCOSC approach may suggest a great way to suppress the large phase segregation of donor and acceptor domains with better morphological stability compared to the blend device.     

Enhanced Thermal Stability and Efficiency of Polymer Bulk‐Heterojunction Solar Cells by Low‐Temperature Drying of the Active Layer

This study addresses two key issues, stability and efficiency, of polymer solar cells based on blended poly(3‐hexylthiophene) (P3HT) and [6,6]‐phenyl‐C61‐butyric acid methyl ester (PCBM) by demonstrating a film‐forming process that involves low‐temperature drying (?5 °C) and subsequent annealing of the active layer. The low‐temperature process achieves 4.70% power conversion efficiency (PCE) and ～1250 h storage half‐life at 65 °C, which are significant improvements over the 3.39% PCE and ～143 h half‐life of the regular room‐temperature process. The improvements are attributed to the enhanced nucleation of P3HT crystallites as well as the minimized separation of the P3HT and PCBM phases at the low drying temperature, which upon post‐drying annealing results in a morphology consisting of small PCBM‐rich domains interspersed within a densely interconnected P3HT crystal network. This morphology provides ample bulk‐heterojunction area for charge generation while allowing for facile charge transport; moreover, the P3HT crystal network serves as an immobile frame at heating temperatures less than the melting point (T_m) of P3HT, thus preventing PCBM/P3HT phase separation and the corresponding device degradation.     

Intraphase Microstructure–Understanding the Impact on Organic Solar Cell Performance

A comprehensive study of the effect of intraphase microstructure on organic photovoltaic (OPV) device performance is undertaken. Utilizing a bilayer device architecture, a small molecule donor (TIPS‐DBC) is deposited by both spin‐coating and by thermal evaporation in vacuum. The devices are then completed by thermal evaporation of C₆₀, an exciton blocking layer and the cathode. This bilayer approach enables a direct comparison of device performance for donor layers in which the same material exhibits subtle differences in microstructure. The electrical performance is shown to differ considerably for the two devices. The bulk and interfacial properties of the donor layers are compared by examination with photoelectron spectroscopy in air (PESA), optical absorption spectroscopy, charge extraction of photo‐generated charge carriers by linearly increasing voltage (photo‐CELIV), time‐resolved photoluminescence measurements, X‐ray reflectometry (XR), and analysis of dark current behavior. The observed differences in device performance are shown to be influenced by changes to energy levels and charge transport properties resulting from differences in the microstructure of the donor layers. Importantly, this work demonstrates that in addition to the donor/acceptor microstructure, the intraphase microstructure can influence critical parameters and can therefore have a significant impact on OPV performance.     

Lending Triarylphosphine Oxide to Phenanthroline: a Facile Approach to High‐Performance Organic Small‐Molecule Cathode Interfacial Material for Organic Photovoltaics utilizing Air‐Stable Cathodes

Cathode interfacial material (CIM) is critical to improving the power conversion efficiency (PCE) and long‐term stability of an organic photovoltaic cell that utilizes a high work function cathode. In this contribution, a novel CIM is reported through an effective and yet simple combination of triarylphosphine oxide with a 1,10‐phenanthrolinyl unit. The resulting CIM possesses easy synthesis and purification, a high T _g of 116 °C and attractive electron‐transport properties. The characterization of photovoltaic devices involving Ag or Al cathodes shows that this thermally deposited interlayer can considerably improve the PCE, due largely to a simultaneous increase in V _oc and FF relative to the reference devices without a CIM. Notably, a PCE of 7.51% is obtained for the CIM/Ag device utilizing the active layer PTB7:PC₇₁BM, which far exceeds that of the reference Ag device and compares well to that of the Ca/Al device. The PCE is further increased to 8.56% for the CIM/Al device (with J _sc = 16.81 mA cm^?2, V _oc = 0.75 V, FF = 0.68). Ultraviolet photoemission spectroscopy studies reveal that this promising CIM can significantly lower the work function of the Ag metal as well as ITO and HOPG, and facilitate electron extraction in OPV devices.     

Quantitative Analysis of Bulk Heterojunction Films Using Linear Absorption Spectroscopy and Solar Cell Performance

A fundamental understanding of the relationship between the bulk morphology and device performance is required for the further development of bulk heterojunction organic solar cells. Here, non‐optimized (chloroform cast) and nearly optimized (solvent‐annealed o‐dichlorobenzene cast) P3HT:PCBM blend films treated over a range of annealing temperatures are studied via optical and photovoltaic device measurements. Parameters related to the P3HT aggregate morphology in the blend are obtained through a recently established analytical model developed by F. C. Spano for the absorption of weakly interacting H‐aggregates. Thermally induced changes are related to the glass transition range of the blend. In the chloroform prepared devices, the improvement in device efficiency upon annealing within the glass transition range can be attributed to the growth of P3HT aggregates, an overall increase in the percentage of chain crystallinity, and a concurrent increase in the hole mobilities. Films treated above the glass transition range show an increase in efficiency and fill factor not only associated with the change in chain crystallinity, but also with a decrease in the energetic disorder. On the other hand, the properties of the P3HT phase in the solvent‐annealed o‐dichlorobenzene cast blends are almost indistinguishable from those of the corresponding pristine P3HT layer and are only weakly affected by thermal annealing. Apparently, slow drying of the blend allows the P3HT chains to crystallize into large domains with low degrees of intra‐ and interchain disorder. This morphology appears to be most favorable for the efficient generation and extraction of charges.     

Charge Transport and Photocurrent Generation in Poly(3‐hexylthiophene): Methanofullerene Bulk‐Heterojunction Solar Cells

The effect of controlled thermal annealing on charge transport and photogeneration in bulk‐heterojunction solar cells made from blend films of regioregular poly(3‐hexylthiophene) (P3HT) and methanofullerene (PCBM) has been studied. With respect to the charge transport, it is demonstrated that the electron mobility dominates the transport of the cell, varying from 10^–8 m² V^–1 s^–1 in as‐cast devices to ≈3 × 10^–7 m² V^–1 s^–1 after thermal annealing. The hole mobility in the P3HT phase of the blend is dramatically affected by thermal annealing. It increases by more than three orders of magnitude, to reach a value of up to ≈ 2 × 10^–8 m² V^–1 s^–1 after the annealing process, as a result of an improved crystallinity of the film. Moreover, upon annealing the absorption spectrum of P3HT:PCBM blends undergo a strong red‐shift, improving the spectral overlap with solar emission, which results in an increase of more than 60 % in the rate of charge‐carrier generation. Subsequently, the experimental electron and hole mobilities are used to study the photocurrent generation in P3HT:PCBM devices as a function of annealing temperature. The results indicate that the most important factor leading to a strong enhancement of the efficiency, compared with non‐annealed devices, is the increase of the hole mobility in the P3HT phase of the blend. Furthermore, numerical simulations indicate that under short‐circuit conditions the dissociation efficiency of bound electron–hole pairs at the donor/acceptor interface is close to 90 %, which explains the large quantum efficiencies measured in P3HT:PCBM blends.     

Low‐Temperature,Nontoxic Water‐Induced Metal‐Oxide Thin Films and Their Application in Thin‐Film Transistors

Here, a simple, nontoxic, and inexpensive “water‐inducement” technique for the fabrication of oxide thin films at low annealing temperatures is reported. For water‐induced (WI) precursor solution, the solvent is composed of water without additional organic additives and catalysts. The thermogravimetric analysis indicates that the annealing temperature can be lowered by prolonging the annealing time. A systematic study is carried out to reveal the annealing condition dependence on the performance of the thin‐film transistors (TFTs). The WI indium‐zinc oxide (IZO) TFT integrated on SiO₂ dielectric, annealed at 300 °C for 2 h, exhibits a saturation mobility of 3.35 cm² V^?1 s^?1 and an on‐to‐off current ratio of ≈10⁸. Interestingly, through prolonging the annealing time to 4 h, the electrical parameters of IZO TFTs annealed at 230 °C are comparable with the TFTs annealed at 300 °C. Finally, fully WI IZO TFT based on YO_x dielectric is integrated and investigated. This TFT device can be regarded as “green electronics” in a true sense, because no organic‐related additives are used during the whole device fabrication process. The as‐fabricated IZO/YO_x TFT exhibits excellent electron transport characteristics with low operating voltage (≈1.5 V), small subthreshold swing voltage of 65 mV dec^?1 and the mobility in excess of 25 cm² V^?1 s^?1.     

Precise Structural Development and its Correlation to Function in Conjugated Polymer: Fullerene Thin Films by Controlled Solvent Annealing

The impact of controlled solvent vapor exposure on the morphology, structural evolution, and function of solvent‐processed poly(3‐hexylthiophene):[6,6]‐phenyl‐C₆₁‐butyric acid methyl ester (P3HT:PCBM) bilayers is presented. Grazing incident wide angle X‐ray scattering (GIWAXS) shows that the crystallization of P3HT increases with solvent exposure, while neutron reflectivity shows that P3HT simultaneously diffuses into PCBM, indicating that an initial bilayer structure evolves into a bulk heterojunction structure. Small angle neutron scattering (SANS) shows the agglomeration of PCBM and the formation of a PCBM pure phase when solvent annealing for 90 min. The structural evolution can be described as occurring in two stages: the first stage combines the enhanced crystallization of P3HT and diffusion of PCBM into P3HT, while the second stage entails the agglomeration of PCBM and formation of a PCBM pure phase. The phase separation of PCBM from P3HT is not driven by P3HT crystallinity, but is due to the concentration of PCBM exceeding the miscibility limit of PCBM in P3HT. Correlation of the morphology to photovoltaic activity shows that device performance significantly improves with solvent annealing for 90 min, indicating that both sufficient P3HT crystallization and formation of a PCBM pure phase are crucial in the optimization of the morphology of the active layer.     

Materials‐Scale Implications of Solvent and Temperature on [6,6]‐Phenyl‐C61‐butyric Acid Methyl Ester (PCBM): A Theoretical Perspective

The ability to detail how molecules pack in the bulk and at the various materials interfaces in the active layer of an organic solar cell is important to further understanding overall device performance. Here, [6,6]‐phenyl‐C₆₁‐butyric acid methyl ester (PCBM), a preferred electron‐acceptor material in organic solar cells, is studied through molecular dynamics (MD) simulations; the goal is to examine the effects of temperature and trace solvents on the packing and morphological features of bulk PCBM. Solubility (miscibility) parameters, melting and order‐disorder transitions, surface energies, and orientational distributions as a function of different starting configurations are discussed. On the basis of the derived morphologies, electronic structure calculations and a kinetic Monte Carlo approach are combined to evaluate the parameters impacting electron mobility in crystalline and amorphous PCBM structures.     

Bipolar Charge Transport in PCPDTBT‐PCBM Bulk‐Heterojunctions for Photovoltaic Applications

An experimental study of the transport properties of a low‐bandgap conjugated polymer giving high photovoltaic quantum efficiencies in the near infrared spectral region (E_g‐opt ～ 1.35 eV) is presented. Using a organic thin film transistor geometry, we demonstrate a relatively high in‐plane hole mobility, up to 1.5 · × 10^?2 cm² V^?1 s^?1 and quantify the electron mobility at 3 × · 10^?5 cm² V^?1 s^?1 on a SiO₂ dielectric. In addition, singular contact behavior results in bipolar quasi‐Ohmic injection both from low and high workfunction metals like LiF/Al and Au. X‐ray investigations revealed a degree of interchain π‐stacking that is probably embedded in a disordered matrix. Disorder also manifests itself in a strong positive field dependence of the hole mobility from the electric field. In blends made with the electron acceptor methanofullerene [6,6]‐phenyl C₆₁ butyric acid methyl ester (PCBM), the transistor characteristics suggest a relatively unfavorable intermixing of the two components for the application to photovoltaic devices. We attribute this to a too fine dispersion of [C60]‐PCBM in the polymer matrix, that is also confirmed by the quenching of the photoluminescence signal measured in PCPDTBT [C60]‐PCBM films with various composition. We show that a higher degree of phase separation can be induced during the film formation by using 1,8‐octanedithiol (ODT), which leads to a more efficient electron percolation in the [C60]‐PCBM. In addition, the experimental results, in combination with those of solar cells seem to support the correlation between the blend morphology and charge recombination. We tentatively propose that the drift length, and similarly the electrical fill factor, can be limited by the recombination of holes with electrons trapped on isolated [C60]‐PCBM clusters. Ionized and isolated [C60]‐PCBM molecules can modify the local electric field in the solar cell by build‐up of a space‐charge. The results also suggest that further improvements of the fill factor may also be limited by a strong electrical‐field dependence of the hole transport.     

Direct Arylation Polycondensation: A Promising Method for the Synthesis of Highly Pure,High‐Molecular‐Weight Conjugated Polymers Needed for Improving the Performance of Organic Photovoltaics

Alternating conjugated polymers of ethylenedioxythiophene and fluorene are prepared using three different synthetic methods to investigate the effects of these synthetic methods on the purity, field‐effect transistor (FET) performance, and organic photovoltaic (OPV) performance of the polymer. In this study, microwave‐assisted direct arylation polycondensation is used to obtain a high‐purity, high‐molecular‐weight (147 kDa) polymer. This pure polymer exhibits a high FET hole mobility of 1.2 × 10^?3 cm² V^?1 s^?1 and high OPV performance with a power conversion efficiency of 4%, even though the polymer forms an amorphous film, which absorbs in a limited region of the spectrum.