Solvent vapor‐induced self assembly and its influence on optoelectronic conversion of poly(3‐hexylthiophene): Methanofullerene bulk heterojunction photovoltaic cells

Nanoscale‐phase separation of electron donor/acceptor blends is crucial for efficient charge generation and collection in polymer bulk heterojunction photovoltaic cells. We investigated solvent vapor annealing effect of poly(3‐hexylthiophene) (P3HT)/methanofullerene (PCBM) blend on its morphology and optoelectronic properties. The organic solvents of choice for the treatment have a major effect on the morphology of P3HT/PCBM blend and the device performance. Ultraviolet‐visible absorption spectroscopy shows that specific solvent vapor annealing can induce P3HT self‐assembling to form well‐ordered structure; and hence, the absorption in the red region and the hole transport are enhanced. The solvent that has a poor solubility to PCBM would cause large PCBM clusters and result in a rough blend film. By combining an appropriate solvent vapor treatment and post‐thermal annealing of the devices, the power conversion efficiency is enhanced. © 2008 Wiley Periodicals, Inc. J Appl Polym Sci, 2009     

Theoretical investigations of electronic structure and charge transport properties in polythiophene‐based organic field‐effect transistors

Regioregular poly(3‐hexylthiophene) (P3HT) is a hole transport polymer material used in organic field‐effect transistors (OFETs) and can reach mobilities as high as 0.1 cm² V^?1 s^?1. Factors that affect the charge mobility and the transport mechanisms of P3HT‐based OFET systems are therefore of great importance. We use quantum mechanical methods to interpret the charge mobility and the transport properties of self‐assembled P3HT molecules along the intra‐chain and inter‐chain directions. Our approach is illustrated by a hopping transport model, in which we examine the variation of charge mobility with torsional angle and the intermolecular distance between two adjacent thiophene segments. We also simulate packed P3HT structures via molecular dynamics (MD) simulations. The MD results indicate that the resultant mobility along the π?π inter‐chain direction is significantly less than that along the intra‐chain direction. Accordingly, the main charge‐transfer route within the P3HT ordered domains is an intra‐chain rather than an inter‐chain one. The calculation result for the inter‐chain hole mobility is around 10^?2 cm² V^?1 s^?1, which is consistent with experimental data from P3HT single fibril. Copyright © 2009 Society of Chemical Industry     

Cocrystallization mechanism of poly(3‐hexyl thiophenes) with different amount of chain regioregularity

The overall crystallization rates of poly (3‐hexyl thiophene) (P3HT) cocrystals with different amount of regioregularity of the components are measured using differential scanning calorimetry (DSC). Two pairs of cocrystals with varying compositions of the component polymers (viz P3HT(R) (regioregularity 92 mol %)/P3HT‐2 (regioregularity 82 mol %), and P3HT‐2/P3HT‐1 (regioregularity 75 mol %)) are used. The crystallization rate at the same isothermal crystallization temperature (T_c) decreases with increasing regioregularity. The low Avrami exponent values (0.15–1.0) in all the samples suggest the presence of rigid amorphous portion, which cannot diffuse out quickly from the crystal growth front (soft impingement). Analysis of crystallization rate using Laurintzen–Hoffman (L–H) growth rate theory indicates Regime I to Regime II transition in all the samples. The product of lateral and end surface energy values (σσ_e) increases gradually with increasing regioirregularity in the blend. Analysis of σ values indicates chain extension of the components in the melt of the blend and the entropy of activation (ΔS_I–II) of the cocrystals are higher than those of the components. The entropy of cocrystallization (ΔS_c) values are 1–2.4 e.u for P3HT(R)/P3HT‐2 system and 0.5–1 e.u for P3HT‐2/P3HT‐1 system. © 2006 Wiley Periodicals, Inc. J Appl Polym Sci 101: 3811–3820, 2006     

Temperature‐conductivity characteristics of the composites consisting of fractionated poly(3‐hexylthiophene) and conducting particles

Poly (3‐hexylthiophene) (P3HT) synthesized by oxidative polymerization was fractionated by molecular weight by using organic solvents. The fraction of higher average molecular weight gave higher regioregularity and conductivity. Composites of the P3HT fraction having the highest molecular weight were prepared by use of the following conducting particles as fillers: titanium carbide (TiC), indium tin oxide (ITO), and carbon black (CB). Temperature‐conductivity profiles of the composites showed that the resistance change with PTC (positive temperature coefficient) effect was strongly influenced by the content and size of conducting particles and the molecular weight of P3HT. Although no significant PTC effect for P3HT‐CB composite and little effect for P3HT‐ITO composite system were observed, the P3HT‐TiC composite containing TiC of 70–80 wt % showed an obvious PTC effect that brought the conductivity change by about four orders of magnitude near the glass transition temperature of P3HT. However, such a remarkable PTC effect was not observed for the P3HT‐TiC composite prepared with the P3HT fraction of low‐molecular weight. It was shown that a good PTC effect could be achieved by the composite consisting of the P3HT of high‐molecular weight and the conducting particles of relatively large size. © 2000 John Wiley & Sons, Inc. J Appl Polym Sci 77: 3069–3076, 2000     

Solvent effects on gravure-printed organic layers of nanoscale thickness for organic solar cells

The effects of different solvents on the fabrication of organic photovoltaic cells by gravure printing are reported. Polymer bulk heterojunction solar cells were fabricated with ITO/PEDOT: PSS/P3HT: PCBM/Al layer structures using 4–9 wt% mixtures of poly(3-hexylthiophene) (P3HT) and [6,6]-phenyl-C61 butyric acid methyl ester (PCBM) in 1,2-dichlorobenzene to optimize solution viscosity for gravure printing. 7 wt% P3HT: PCBM showed optimal efficiency of 1.64% and resulted in an active layer 340 nm thick. Three solvents, 1,2-dichlorobenzene, chloroform, and chlorobenzene, were tested and a 1: 1 ratio mixture of 1,2-dichlorobenzene and chloroform resulted in the best efficiency of 2.21%. This study demonstrates the importance of solvent effects in the gravure printing of organic photovoltaic devices.     

溶剂对刮涂法制备P3HT:PCBM活性层薄膜形貌及光电性能的影响

选用2种混合溶剂氯仿+四氢化萘和二氯苯+氯仿配制活性液,通过刮涂法制备了P3HT∶PCBM活性层,研究了不同溶剂物化参数对P3HT∶PCBM活性层薄膜形貌及其组装电池光电性能的影响。应用显微图像分析仪、紫外可见分光光度计和台阶仪对P3HT∶PCBM活性层薄膜形貌进行了表征;采用X-射线衍射仪和紫外可见分光光度计分别测试了P3HT∶PCBM活性层的晶型结构和吸收光谱;在AM 1.5G、100mW/cm2光照下,测试了电池的光电性能。结果表明:采用二氯苯+氯仿(9∶1)混合溶剂较氯仿+四氢化萘(19∶1)混合溶剂制备的薄膜具有良好的均一性、平滑度、晶体结构,长吸收波长,用其组装的大面积(4cm2)柔性有机太阳能电池光电转换效率提高37%。     

Regioregular improvement on the oxidative polymerization of poly‐3‐octylthiophenes by slow addition of oxidant at low temperature

Many pathways can be used to synthesize polythiophenes derivatives. The polycondensation reactions performed with organometallics are preferred since they lead to regioregular polymers (with high content of heat‐to‐tail coupling) which have enhanced conductivity and luminescence. However, these pathways have several steps; the reactants are highly moisture sensitive and expensive. On the other hand, the oxidative polymerization using FeCl₃ is a one‐pot reaction that requires less moisture sensitive reactants with lower cost, although the most common reaction conditions lead to polymers with low regioregularity. Here, we report that by changing the reaction conditions, such as FeCl₃ addition rate and reaction temperature, poly‐3‐octylthiophenes with different the regioregularities can be obtained, reaching about 80% of heat‐to‐tail coupling. Different molar mass distributions and polydispersivities were obtained. The preliminary results suggest that the oxidative polymerization process could be improved to yield polythiophenes with higher regioregularity degree and narrower molar mass distributions by just setting some reaction conditions. We also verified that it is possible to solvent extract part of the lower regioregular fraction of the polymer further improving the regioregularity degree. © 2011 Wiley Periodicals, Inc. J Appl Polym Sci, 2012     

Effect of [6,6]‐phenyl‐C61‐butyric acid methyl ester on the morphology of poly(3‐hexylthiophene) film

The change of morphology of poly(3‐hexylthiophene) (P3HT) film as a result of blending with [6,6]‐phenyl‐C₆₁‐butyric acid methyl ester (PCBM) was studied using a freeze‐dry method. A porous structure was observed as the P3HT/PCBM solution was freeze‐dried. The pore size decreased as the proportion of PCBM increased in the P3HT/PCBM blended film. Additionally, the freeze‐dried P3HT/PCBM film was more resistant to the formation of PCBM crystals than that prepared by a spin‐coating method during the thermal annealing process. Homogeneous distribution of PCBM in the freeze‐dried P3HT/PCBM film was the main reason for the reduction of large PCBM crystal formation. Copyright © 2011 Society of Chemical Industry     

A new method to disperse CdS quantum dot-sensitized TiO2 nanotube arrays into P3HT:PCBM layer for the improvement of efficiency of inverted polymer solar cells

We report that the efficiency of ITO/nc-TiO₂/P3HT:PCBM/MoO₃/Ag inverted polymer solar cells (PSCs) can be improved by dispersing CdS quantum dot (QD)-sensitized TiO₂ nanotube arrays (TNTs) in poly (3-hexylthiophene) and [6,6]-phenyl-C₆₁-butyric acid methyl ester (P3HT:PCBM) layer. The CdS QDs are deposited on the TNTs by a chemical bath deposition method. The experimental results show that the CdS QD-sensitized TNTs (CdS/TNTs) do not only increase the light absorption of the P3HT:PCBM layer but also reduce the charge recombination in the P3HT:PCBM layer. The dependence of device performances on cycles of CdS deposition on the TNTs was investigated. A high power conversion efficiency (PCE) of 3.52% was achieved for the inverted PSCs with 20 cyclic depositions of CdS on TNTs, which showed a 34% increase compared to the ITO/nc-TiO₂/P3HT:PCBM/MoO₃/Ag device without the CdS/TNTs. The improved efficiency is attributed to the improved light absorbance and the reduced charge recombination in the active layer.     

Synthesis and characterization of three‐arm star‐shaped conjugated poly(3‐hexylthiophene)s: impact of the core structure on optical properties

Star‐shaped molecules consisting of regioregular poly(3‐hexylthiophene) (P3HT) chains as the arms, attached to either a propeller‐like triphenylamine or a planar triphenylbenzene core, have been synthesized via Suzuki coupling. The structures of the three‐arm star‐shaped poly(3‐hexylthiophene) (s‐P3HT) materials obtained were studied using Fourier transform infrared, ¹H and ¹³C NMR, XRD, gel permeation chromatography and DSC. The s‐P3HT polymers were soluble in common organic solvents and exhibited number‐average molecular weights of 6000–7200 g mol^?1. Their optical properties in solutions and in solid state films were investigated using the UV?visible absorption and photoluminescence techniques, and were compared with those of linear P3HT. © 2015 Society of Chemical Industry     

Synthesis and characterization of novel fulleropyrrolidine in P3HT blended bulk heterojunction solar cells

Synthesis of novel fullerene derived electron acceptors and characterization of their organic photovoltaic (OPV) properties is important for advancing fundamental knowledge towards developing next generation organic solar cells. We report the synthesis of a novel fulleropyrrolidine derivative C60-fused N-(3-methoxypropyl)-2-(carboxyethyl)-5-(4-cyanophenyl)fulleropyrrolidine (NCPF) by 1,3-dipolar cycloaddition reaction and characterization of NCPF by ¹H NMR, ¹³C NMR, MALDI-TOFMS, FT-IR, UV–Vis and CV. The synthesized NCPF fullerene derivative showed good solubility in common organic solvents such as chlorobenzene and 1,2 dichlorobenzene important for film formation, with optical absorbance and electronic properties comparable to PCBM. Optical micrographs of P3HT:PCBM thin films reveal formation of sparse, phase segregated needle shape PCBM micro-crystalline aggregates after 1 h of annealing at 150 °C whose length follows nucleation and growth kinetics over 24 h. In contrast, the P3HT:NCPF thin films exhibit homogeneity over 24 h, possibly due to weaker interparticle vanderWaals forces and/or stronger interactions with P3HT. This long term morphological stability of P3HT:NCPF is important for extended use in OPV applications. At an order of magnitude smaller scale, AFM of as cast and 10 min annealed at 150 °C P3HT:PCBM and P3HT:NCPF films reveal mostly smooth surfaces, with some NCPF cluster formation. Grazing incidence wide angle X-ray scattering (GIWAXS) measurements of P3HT:NCPF films indicate an increase of P3HT crystallinity with thermal annealing, leading to improvement in device performance. Photovoltaic devices fabricated with the active layer of P3HT:NCPF and P3HT:PCBM sandwiched between ITO/PEDOT:PSS and Al layer showed comparable performance upon short term annealing.     

Orientation control of regioregular‐poly(3‐dodecylthiophene) films formed by the friction‐transfer method and the performance of organic photovoltaic devices based on these films

Control of the molecular orientation of regioregular poly(3‐alkylthiophene)s (RR‐P3ATs) improves the performance of field‐effect transistors and organic photovoltaic devices (OPVs). However, most thiophene ring planes of the RR‐P3AT molecules (except RR‐poly(3‐butylthiophene)) in films formed by the conventional spin‐coating method stand on the substrate, that is, edge‐on orientation. Orientation control of RR‐poly(3‐dodecylthiophene) (RR‐P3DDT) molecules in films formed by the friction transfer method is reported and the performance of OPVs based on friction‐transferred RR‐P3DDT films is compared to that of OPVs based on spin‐coated films. The films are investigated by polarized ultraviolet–visible light absorption spectroscopy, Fourier transform infrared spectroscopy, and grazing‐incidence X‐ray diffraction measurement. For friction‐transferred films, the RR‐P3DDT molecular chain is uniaxially aligned parallel to the substrate plane. In addition, the thiophene ring planes of the RR‐P3DDT molecules are also oriented parallel to the substrate plane, that is, face‐on orientation. The power conversion efficiency (PCE) and fill factor of the RR‐P3DDT/C₆₀ bilayer OPVs based on the friction‐transferred RR‐P3DDT films are higher than those of devices based on spin‐coated films. The PCE and photocurrent of the device based on the friction‐transferred film are larger under irradiation with polarized light parallel to the RR‐P3DDT molecular chain direction than with polarized light orthogonal to the chain direction. © 2013 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2014 , 131, 40136.     

Simple strategy to tune the charge transport properties of conjugated polymer/carbon nanotube composites using an electric field assisted deposition technique

Work concerning the incorporation of carbon nanotubes (CNTs) in organic semiconducting polymers have now been reported by many research groups, and the electrical properties of polymer/CNT nanocomposites have been extensively studied. In this work, we present a simple procedure to tune the charge transport properties of planar organic polymer films based on poly(3‐hexylthiophene) (P3HT). The polymer/CNT composites are simultaneously processed and oriented from solution using an electric field assisted orientation technique. We first study the behavior of CNTs alone during the alignment procedure and emphasize the main experimental parameters that drive their final orientation on the substrate. By quantitatively analyzing the CNT angular distribution on the substrate, we show that the dielectric constant of the solvent used to disperse and deposit the CNTs is crucial to ensure an efficient orientation, and that a dielectrophoresis‐like orientation procedure occurs. The transposition of this approach to planar P3HT/CNT composites is made by investigating the electric properties in ambient conditions of aligned and non‐aligned devices. Current–voltage characteristics show a drastic increase of the composite conductivity upon addition and alignment of CNTs. Field‐effect transistor charge mobilities are improved by an order of magnitude upon addition of CNT (1 wt%) in P3HT, and another decade is gained using the optimized alignment parameters, without any additional annealing. These results demonstrate the strong potentialities of our approach in the field of printed electronics and organic optoelectronics. © 2013 Society of Chemical Industry     

Efficiency above 6% in poly(3‐hexylthiophene):phenyl‐C‐butyric acid methyl ester photovoltaics via simultaneous addition of poly(3‐hexylthiophene) based grafted graphene nanosheets and hydrophobic block copolymers

A combination of reduced graphene oxide (rGO) nanosheets grafted with regioregular poly(3‐hexylthiophene) (P3HT) (rGO‐g‐P3HT) and P3HT‐b‐polystyrene (PS) block copolymers was utilized to modify the morphology of P3HT:[6,6]‐phenyl‐C71‐butyric acid methyl ester (PC71BM) active layers in photovoltaic devices. Efficiencies greater than 6% were acquired after a mild thermal annealing. To this end, the assembling of P3HT homopolymers and P3HT‐b‐PS block copolymers onto rGO‐g‐P3HT nanosheets was investigated, showing that the copolymers were assembled from the P3HT side onto the rGO‐g‐P3HT nanosheets. Assembling of P3HT‐b‐PS block copolymers onto the rGO‐g‐P3HT nanosheets developed the net hole and electron highways for charge transport, thereby in addition to photoluminescence quenching the charge mobility (μ_h and μ_e) values increased considerably. The best charge mobilities were acquired for the P3HT₅₀₀₀₀:PC71BM:rGO‐g‐P3HT₅₀₀₀₀:P3HT₇₀₀₀‐b‐PS₁₀₀₀ system (μ_h = 1.9 × 10^?5 cm² V^–1 s^–1 and μ_e = 0.8 × 10^?4 cm² V^–1 s^–1). Thermal annealing conducted at 120 °C also further increased the hole and electron mobilities to 9.8 × 10^?4 and 2.7 × 10^?3 cm² V^–1 s^–1, respectively. The thermal annealing acted as a driving force for better assembly of the P3HT‐b‐PS copolymers onto the rGO‐g‐P3HT nanosheets. This phenomenon improved the short circuit current density, fill factor, open circuit voltage and power conversion efficiency parameters from 11.13 mA cm^?2, 0.63 V, 62% and 4.35% to 12.98 mA cm^?2, 0.69 V, 68% and 6.09%, respectively. © 2019 Society of Chemical Industry     

Towards optimization of functionalized single-walled carbon nanotubes adhering with poly(3-hexylthiophene) for highly efficient polymer solar cells

In this paper, we present the optimization of single-walled carbon nanotubes (SWCNTs) by acid-treatment, solution ultrasonication time and dispersion in photoactive layer for efficient organic solar cells. After non-covalently adhering with poly(3-hexylthiophene) (P3HT), pre-functionalized SWCNTs were blended into the composites of P3HT and [6,6]-phenyl-C₆₁-butyric acid methyl ester (PCBM) as photoactive layer, and a maximum power conversion efficiency (PCE) of 3.02% with a short-circuit current density of 11.46 mA/cm² was obtained from photovoltaic cell indium-tin oxide (ITO)/poly(ethylene-dioxythiophene):poly(4-styrenesulfonate) (PEDOT:PSS)/P3HT:PCBM:SWCNTs/Al with an optimum 0.3 wt% SWCNTs in P3HT:PCBM:SWCNTs nanocomposite, the PCE can be enhanced by more than 10% as compared to the control device ITO/PEDOT:PSS/P3HT:PCBM/Al. The performance improvement by incorporating with functionalized SWCNTs is mainly attributed to the extension of excitons dissociation area and fastening charge carriers transfer across the active layer.     

Morphology,structure, and photovoltaic properties of poly(3‐hexylthiophene) and [6,6]‐phenyl‐C61‐butyric acid methyl ester‐based ternary blends doping with polystyrene of different tacticities

The influence of the polystyrene of different tacticities on the morphology, phase structure, and photovoltaic properties of poly(3‐hexylthiophene) (P3HT) and [6,6]‐phenyl‐C61‐butyric acid methyl ester (PCBM) blend has been extensively investigated. The atactic polystyrene (aPS) immiscible with P3HT tended to form the phase‐separated and columnar structure at low aPS weight ratio. Besides, the aPS could migrate to the surface of the films with PCBM phase distributing in the interfaces between P3HT and aPS domains at high aPS weight ratio of 75 wt %. The syndiotactic polystyrene (sPS) immiscible with P3HT could induce the crystallization of P3HT at low weight ratio of 3 wt %. The device based on aPS/P3HT/PCBM ternary blend showed of power conversion efficiency (PCE) of 1.2% even at aPS weight ratio of 50 wt %. However, the device based on sPS/P3HT/PCBM exhibited a sharp decrease in PCE value from 2.3% to 0.6% at sPS weight ratio of 3 wt %, due to the change in film morphology. The performance of the solar cell is believed to be determined by the morphology and phase structure of the ternary blends as revealed by the atomic force microscopy and UV‐vis spectra analysis. © 2015 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2015 , 132, 41823.     

Butterfly nanostructures via regioregularly grafted multi‐walled carbon nanotubes and poly(3‐hexylthiophene) to improve photovoltaic characteristics

Butterfly nanostructures were designed using multi‐walled carbon nanotubes (CNTs) grafted with regioregular poly(3‐hexylthiophene) (RR‐P3HT) chains (CNT‐graft‐P3HT). The secondary crystallization of RR‐P3HT free chains onto CNT‐graft‐P3HT reflected the donor–acceptor supramolecules with a butterfly configuration, in which the CNT acted as the body of the butterfly and seeded crystallization of P3HT free chains resulted in the wings having a width of 37–38 nm. Butterfly supramolecules demonstrated high melting point (241.2 °C), fusion enthalpy (31.5 J g^?1) and crystallinity (85.13%). High photoluminescence quenching and thus donating–accepting property were also detected for the butterfly nanohybrids with a bandgap energy of 1.94 eV. Incorporation of butterfly nanostructures in the active layer of photovoltaic devices (P3HT:butterfly) conspicuously affected the system characteristics including short circuit current density (J_sc; 10.84 mA cm^?2), fill factor (FF; 56%) and power conversion efficiency (PCE; 3.94%). The inclusion of phenyl‐C71‐butyric acid methyl ester molecules as second acceptor in thin‐film active layers further increased the efficacy of systems, i.e. J_sc of 12.23 mA cm^?2, FF of 63%, open circuit voltage of 0.66 V and PCE of 5.08%, without considering external treatments and additives. © 2018 Society of Chemical Industry     

A comparative study on the influence of alkyl thiols on the structural transformations in P3HT/PCBM and P3OT/PCBM blends

Herein, we present a comparative study on the structural transformations in P3HT/PCBM and P3OT/PCBM blends using octane (C₈) and dodecane (C₁₂) thiols as solvent additives. Addition of dodecane thiol to the blends promotes needle-like PCBM crystal formation. These crystals are found abundant in P3OT/PCBM and less in P3HT/PCBM blend and are identified by SAXS, DSC and SEM measurements. Using polymer of two different tail lengths, the SAXS results provide the first experimental support on the recent findings on fullerene intercalation around the crystalline boundaries in a semi-crystalline polymer. The UV–Visible measurements reveal that the absorption maximum show an appreciable red-shift and photoluminescence spectra infers that the donor/acceptor interface is mostly retained, upon dodecane thiol addition. These needle-like PCBM crystals obtained by annealing free approach in the blends and their dependence on the alkyl tail length of the polymer, would pave way for more effective design of organic photovoltaic devices.     

Fabrication of highly ordered P3HT:PCBM nanostructures and its application as a supercapacitive electrode

In this paper, we successfully demonstrated the fabrication of highly ordered and large-scale P3HT:PCBM nanowires via a slow-drying method, which allows for the convenient and cost-effective preparation of well-defined P3HT:PCBM nanostructures with large domains. The formation of the organic nanowires can be explained by the self-organization of polymer chains under favorable thermodynamic conditions in the slow-drying process. Furthermore, the C-V measurements revealed that the P3HT:PCBM nanowires possess high capacitance. This supercapacitive behavior of the nanowires is related to their large surface area and open structure, which can facilitate ion transport and accumulation. Owing to their extremely easy preparation and excellent capacitance performance, the P3HT:PCBM nanowires offer a promising electrode material for supercapacitor devices.     

Investigating the reduction in the absorption intensity of P3HT in polymer/fullerene “bilayers” coated using orthogonal solvents

We investigated the reduction in the absorption intensity of poly(3‐hexylthiophene) (P3HT) in a poly(3‐hexylthiophene)/(6,6)‐phenyl‐C₆₁‐butyric acid methyl ester (P3HT/PCBM) “bilayer” heterojunction film that was fabricated using orthogonal solvents. The results show that even though P3HT is insoluble in dichloromethane (DCM), DCM could decrease the chain packing and the crystallinity of the P3HT film by the swelling effect. DCM also assists in the penetration of the PCBM into the P3HT underlayer during spin‐coating. After the DCM evaporates, the PCBM in the P3HT matrix hinders the self‐reorganization of P3HT, causing a drop in the absorption intensity of P3HT. © 2014 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2015 , 132, 41757.