Non-peripheral octahexylphthalocyanine doping effects in bulk heterojunction polymer solar cells

The improvement of long-wavelength sensitivity in bulk heterojunction organic thin-film solar cells based on poly(3-hexylthiophene) (P3HT) by the addition of the soluble phthalocyanine derivative, 1,4,8,11,15,18,22,25-octahexylphthalocyanine (C6PcH₂) is reported. C6PcH₂ possesses near-infrared absorption and can be mixed with a P3HT:1-(3-methoxy-carbonyl)-propyl-1-1-phenyl-(6,6)C61 (PCBM) bulk heterojunction active layer. By doping C6PcH₂, the photosensitivity in the long-wavelength region was improved, and the energy conversion efficiency reached 3.0% at a composition ratio of P3HT:C6PcH₂:PCBM = 10:3:10. We discuss the principle of photoconversion in the bulk heterojunction solar cell based on the P3HT:C6PcH₂:PCBM active layer by taking into consideration the existence of both highly ordered P3HT domains and hexagonal columnar structures of C6PcH₂, and the microphase separation of P3HT and C6PcH₂ in the active layer.     

Correlating dilute solvent interactions to morphology and OPV device performance

Solvent additives have been explored as a reliable way to control the morphology in bulk-heterojunction (BHJ) layers for improved device performance. We show that the choice of solvent additives has direct implications on morphological evolution, i.e. poly(3-hexylthiophene) (P3HT): [6,6]-phenyl C61-butyric acid methyl ester (PCBM) BHJ films processed with a small amount of 1,8-diiodooctane or 1-chloronaphthalene have more crystalline PCBM domains compared to crystalline P3HT domains, while the opposite is true for films cast with nitrobenzene additive and films cast purely from chlorobenzene. The BHJ film cross-links when annealed at 300 °C in the presence of 1,8-diiodooctane. Cross-linking is found to occur even in pristine P3HT and PCBM films annealed under similar conditions. NMR spectroscopy is presented as a viable technique for quantitative analysis of the amount of solvents left in the BHJ films before and after heat treatment. Despite differences in the ways the additives affect the morphology of the BHJ layer, device performance remained stable over 300 h for all additives tested.     

Effect of Alkyl Side‐Chain Length on Photovoltaic Properties of Poly(3‐alkylthiophene)/PCBM Bulk Heterojunctions

The morphological, bipolar charge‐carrier transport, and photovoltaic characteristics of poly(3‐alkylthiophene) (P3AT):[6,6]‐phenyl‐C61‐butyric acid methyl ester (PCBM) blends are studied as a function of alkyl side‐chain length m, where m equals the number of alkyl carbon atoms. The P3ATs studied are poly(3‐butylthiophene) (P3BT, m = 4), poly(3‐pentylthiophene) (P3PT, m = 5), and poly(3‐hexylthiophene) (P3HT, m = 6). Solar cells with these blends deliver similar order of photo‐current yield (exceeding 10 mA cm^?2) irrespective of side‐chain length. Power conversion efficiencies of 3.2, 4.3, and 4.6% are within reach using solar cells with active layers of P3BT:PCBM (1:0.8), P3PT:PCBM (1:1), and P3HT:PCBM (1:1), respectively. A difference in fill factor values is found to be the main source of efficiency difference. Morphological studies reveal an increase in the degree of phase separation with increasing alkyl chain length. Moreover, while P3PT:PCBM and P3HT:PCBM films have similar hole mobility, measured by hole‐only diodes, the hole mobility in P3BT:PCBM lowers by nearly a factor of four. Bipolar measurements made by field‐effect transistor showed a decrease in the hole mobility and an increase in the electron mobility with increasing alkyl chain length. Balanced charge transport is only achieved in the P3HT:PCBM blend. This, together with better processing properties, explains the superior properties of P3HT as a solar cell material. P3PT is proved to be a potentially competitive material. The optoelectronic and charge transport properties observed in the different P3AT:PCBM bulk heterojunction (BHJ) blends provide useful information for understanding the physics of BHJ films and the working principles of the corresponding solar cells.     

Structural control of bulk heterojunction films based on oligothiophene with sterically-bulky groups

Organic photovoltaic solar cells based on oligothiophene and fullerene have been investigated intensively. Until now, the morphologies of bulk heterojunction (BHJ) structures based on oligothiophene and fullerene have been difficult to control because the oligothiophene molecules have lacked substituent groups and therefore have interacted strongly with one another to the point of aggregating into microfibril structures.We succeeded in fabricating homogeneous oligothiophene:C₆₀ BHJ films by adding sterically-bulky groups to oligothiophene in order to control the extent of aggregation. We found that the aggregation onset and maximum fill factor occurred at higher oligothiophene concentrations in BHJ films with C₆₀ for the substituted molecules – the ratio that provides as much oligothiophene as possible for good photovoltaic performance but not so much as to incur aggregation-fill factor was improved. Here in, we report the morphologies and photovoltaic performances of single-component oligothiophene films and BHJ films based on oligothiophenes.     

Photovoltaic Function and Exciton/Charge Transfer Dynamics in a Highly Efficient Semiconducting Copolymer

Exciton dissociation is a key step for the light energy conversion to electricity in organic photovoltaic (OPV) devices. Here, excitonic dissociation pathways in the high‐performance, low bandgap “in‐chain donor–acceptor” polymer PTB7 by transient optical absorption (TA) spectroscopy in solutions, neat films, and bulk heterojunction (BHJ) PTB7:PC₇₁BM (phenyl‐C₇₁‐butyric acid methyl ester) films are investigated. The dynamics and energetics of the exciton and intra‐/intermolecular charge separated states are characterized. A distinct, dynamic, spectral red‐shift of the polymer cation is observed in the BHJ films in TA spectra following electron transfer from the polymer to PC₇₁BM, which can be attributed to the time evolution of the hole–electron spatial separation after exciton splitting. Effects of film morphology are also investigated and compared to those of conjugated homopolymers. The enhanced charge separation along the PTB7 alternating donor–acceptor backbone is understood by intramolecular charge separation through polarized, delocalized excitons that lower the exciton binding energy. Consequently, ultrafast charge separation and transport along these polymer backbones reduce carrier recombination in these largely amorphous films. This charge separation mechanism explains why higher degrees of PCBM intercalation within BHJ matrices enhances exciton splitting and charge transport, and thus increase OPV performance. This study proposes new guidelines for OPV materials development.     

Influence of Solvent Additive 1,8‐Octanedithiol on P3HT:PCBM Solar Cells

Processing solvent additives in polymer:fullerene bulk heterojunction systems are known as a promising method to enhance photovoltaic performance. It is generally agreed that solvent additives enable polymers to have a high degree of molecular order which increases the device performance. However, the understanding of the efficiency enhancement is not complete. There is a lack of insight regarding the quantitative determination of the molecular miscibility between polymer and fullerene as well as the inner morphology changes induced by the additives. In this work, understanding of the influence of the solvent additive 1,8‐octanedithiol (ODT) is provided on the classic system poly(3‐hexylthiophene‐2,5‐diyl):[6,6]‐phenyl‐C61 butyric acid methyl ester (P3HT:PCBM) films. The impact on polymer crystallinity, surface structure, inner morphology, and quantitative molecular miscibility of P3HT and PCBM is studied as a function of ODT volume concentration. The crystallinity is probed with absorption spectroscopy and grazing incidence wide‐angle X‐ray scattering. The morphology and miscibility are characterized via atomic force microscopy and time‐of‐flight grazing incidence small angle neutron scattering. Besides an increased crystallinity and prominent phase separation, ODT increases the solubility of PCBM in P3HT and reduces the size of amorphous P3HT domains. Moreover, solvent processing with a high ODT concentration alters the vertical material composition of the active layer.     

Time‐Dependent Morphology Evolution by Annealing Processes on Polymer:Fullerene Blend Solar Cells

Changes in the nanoscale morphologies of the blend films of poly (3‐hexylthiophene) (P3HT) and [6,6]‐phenyl‐C₆₁‐butyric acid methyl ester (PCBM), for high‐performance bulk‐heterojunction (BHJ) solar cells, are compared and investigated for two annealing treatments with different morphology evolution time scales, having special consideration for the diffusion and aggregation of PCBM molecules. An annealing condition with relatively fast diffusion and aggregation of the PCBM molecules during P3HT crystallization results in poor BHJ morphology because of prevention of the formation of the more elongated P3HT crystals. However, an annealing condition, accelerating PCBM diffusion after the formation of a well‐ordered morphology, results in a relatively stable morphology with less destruction of crystalline P3HT. Based on these results, an effective strategy for determining an optimized annealing treatment is suggested that considers the effect of relative kinetics on the crystallization of the components for a blend film with a new BHJ materials pair, upon which BHJ solar cells are based.     

Three‐Dimensional Bulk Heterojunction Morphology for Achieving High Internal Quantum Efficiency in Polymer Solar Cells

Here, an investigation of three‐dimensional (3D) morphologies for bulk heterojunction (BHJ) films based on regioregular poly(3‐hexylthiophene) (P3HT) and [6,6]‐phenyl‐C₆₁‐butyric acid methyl ester (PCBM) is reported. Based on the results, it is demonstrated that optimized post‐treatment, such as solvent annealing, forces the PCBM molecules to migrate or diffuse toward the top surface of the BHJ composite films, which induces a new vertical component distribution favorable for enhancing the internal quantum efficiency (η_IQE ) of the devices. To investigate the 3D BHJ morphology, novel time‐of‐flight secondary‐ion mass spectroscopy studies are employed along with conventional methods, such as UV‐vis absorption, X‐ray diffraction, and high‐resolution transmission electron microscopy studies. The η_IQE of the devices are also compared after solvent annealing for different times, which clearly shows the effect of the vertical component distribution on the performance of BHJ polymer solar cells. In addition, the fabrication of high‐performance P3HT:PCBM solar cells using the optimized solvent‐annealing method is reported, and these cells show a mean power‐conversion efficiency of 4.12% under AM 1.5G illumination conditions at an intensity of 100 mW cm^?2.     

Molecular-weight-dependent nanoscale morphology in silole-containing cyclopentadithiophene polymer and fullerene derivative blends

We have investigated the effect of polymer molecular weight (MW) on the morphology and efficiency of bulk heterojunction (BHJ) solar cells comprised of poly[(4,4′-bis(2-ethylhexyl)dithieno[3,2-b:2′,3′-d]silole)-2,6-diyl-alt-(5,5′-thienyl-4,4′-dihexyl-2,2′-bithiazole)-2,6-diyl] (Si-PCPDTTBT) and [6,6]-phenyl C₆₁ butyric acid methyl ester (PCBM). Striking morphological changes are observed in BHJ films upon the change of the polymer MW. Atomic force microscopy and transmission electron microscopy studies suggest that high MW polymer generated high degree of phase separation, leading to formation of an interpenetrating network for carrier transport. The X-ray diffraction investigation indicated that increased π–π stacking in Si-PCPDTTBT with increasing polymer MWs results in an increase in hole mobility of Si-PCPDTTBT and electron mobility of PCBM as well as the red shift absorption spectrum in BHJ films. The solar cells based on PCBM with high-MW Si-PCPDTTBT deliver power conversion efficiencies of 3.33%.     

The effect of processing solvent dependent film aggregation on the photovoltaic performance of squaraine:PC71BM bulk heterojunction solar cells

In this work, we systemically investigated the processing solvent-dependent aggregation behavior of a squaraine dye, 2,4-bis[4-(N,N-dibutylamino)-2,6- dihydroxyphenyl] squaraine (DBSQ), in a DBSQ: [6,6]-phenyl-C71-butyric acid methyl ester (PC₇₁BM) blend film, as well as the aggregation effect on the photovoltaic performance of DBSQ:PC₇₁BM bulk heterojunctions (BHJs). Our finding shows that the aggregation behavior of DBSQ dye in the blend film can be controlled via the proper selection of the processing solvents. For a J-aggregate (head-to-tail molecule alignment) DBSQ:PC₇₁BM active layer based BHJ cells, a power conversion efficiency (PCE) of over 5% can be obtained, which is 75% higher than that of the H-aggregate (parallel molecule packing) active layer based BHJ cells. Our results indicate that the processing solvent controlled J-aggregation formation shall be considered as effective approach to tune the optical and electrical properties of thin films for high-performance BHJ solar cells.     

Efficient bulk heterojunction photovoltaic devices based on diketopyrrolopyrrole containing small molecule as donor and modified PCBM derivatives as electron acceptors

A new solution processable small molecule (DPP-CN) containing electron donor diketopyrrolopyrrole (DPP) core and cyanovinylene 4-nitrophenyl (CN) electron acceptor has synthesized for use as the donor material in the bulk heterojunction organic solar cells along with PCBM, modified PCBM i.e. F and A as electron acceptor. It showed a broad absorption in longer wavelength region having optical band gap around 1.64 eV. We have used PCBM, F and A as electron acceptor for the fabrication of bulk heterojunction photovoltaic devices. The power conversion efficiency (PCE) of the BHJ devices based on DPP-CN:PCBM, DPP-CN:F and DPP-CN:A blends cast from the THF solvent is 1.83%, 2.79% and 2.83%, respectively. The increase in the PCE based on F and A as electron acceptor is mainly due to the increase in both short circuit current (J_sc) and open circuit voltage (V_oc). The PCE value of the photovoltaic devices based on the blends DPP-CN:PCBM, DPP-CN:F and DDP-CN:A cast from the mixed solvents (DIO/THF) has been further improved up to 2.40%, 3.32% and 3.34%, respectively. This improvement is mainly due to the increased value of J_sc, which is attributed not only to the increase of crystallinity, but also to the morphological change in the film cast from mixed solvent. Finally, the device ITO/PEDOT:PSS/DPP-CN:A (DIO/THF cast)/TiO₂/Al device shows a PCE of 3.9%. The improved device performance could be attributed to the electron transporting and hole-blocking capabilities due to the introduced TiO₂ buffer layer.     

Laser-induced crystallization and conformation control of poly(3-hexylthiophene) for improving the performance of organic solar cells

Femto-second laser irradiation on P3HT:PCBM solutions have been demonstrated to have a significant impact on the conformational structures and photovoltaic performance of the resultant thin films. The crystallinity and edge-on/face-on conformations of P3HT and the aggregation of PCBM can be manipulated by controlling the wavelength (400–800 nm) and illumination duration (1–3 h) of the lasers. Grazing incidence wide- and small-angle X-ray scattering (GIWAXS and GISAXS) have been simultaneously utilized to characterize the nanostructures of the P3HT:PCBM blend films spin-cast from pristine and laser-irradiated solutions. The results show that the crystallinity, π-π* stacking and face-on conformations of P3HT can be enhanced as a result of the laser irradiation at 500 nm for 3 h. Furthermore, the diffusion and aggregation of PCBM molecules are suppressed by the photo-induced dimerization, as evidenced by the Raman spectra of the films cast from laser-irradiated PCBM solutions. The time-resolved fluorescence decay profiles show the charge transfer efficiency is improved, which may correlate to the supramolecular ordering of the polythiophene chains and the optimized phase separation in P3HT:PCBM composite. In the P3HT:PCBM active layer of the organic solar cells, more efficient charge transport and fine interpenetrating networks can be achieved due to the improved conformational microstructures. Consequently, the short-circuit current densities and power conversion efficiencies can be enhanced in organic solar cells based on the laser-irradiation processed P3HT:PCBM solutions.     

The Influence of Solubilizing Chain Stereochemistry on Small Molecule Photovoltaics

Three stereochemically pure isomers and two isomeric mixtures of a solution‐processable diketopyrrolopyrrole‐containing oligothiophene ( SMDPPEH ) have been used to study the effect of 2‐ethylhexyl solubilizing group stereochemistry on the film morphology and bulk heterojunction (BHJ) solar cell characteristics of small molecule organic photovoltaics. The different SMDPPEH stereoisomer compositions exhibit nearly identical optoelectronic properties in the molecularly dissolved state, as well as in amorphous films blended with PCBM. However, for films in which SMDPPEH crystallization is induced by thermal annealing, significant differences in molecular packing between the different stereoisomer formulations are observed. These differences are borne out in photovoltaic device characteristics for which unannealed devices show very similar behavior, while after annealing the RR‐ and SS‐SMDPPEH enantiomers show blue‐shifted peak EQE relative to the SMDPPEH isomer mixtures. Unannealed devices made from the most crystalline stereoisomer, meso RS‐SMDPPEH , are not completely amorphous, and show improved photocurrent generation as a result. Unlike the other compounds, after thermal annealing the RS‐SMDPPEH devices show reduced device performance. The results reveal that the chirality of commonly used 2‐ethylhexyl solubilizing chains can have a significant effect on the morphology, absorption, and optimum processing conditions of small molecule organic thin films used as photovoltaic device active layers.     

Regulation of the performance parameters of poly(3-alkylthiophene)/[6,6]-phenyl C61-butyric acid methyl ester solar cells by 1,2,3,4-bis(p-methylbenzylidene) sorbitol

Differential scanning calorimetry (DSC) and atomic force microscopy (AFM) measurements indicate that 1,2,3,4-bis(p-methylbenzylidene) sorbitol (MDBS) is a nucleating agent for both poly(3-alkylthiophene)s (P3ATs) and [6,6]-phenyl C₆₁-butyric acid methyl ester (PCBM), but the intermolecular interaction between P3AT and MDBS is stronger than that between PCBM and MDBS. MDBS regulates the crystallization kinetics of P3AT in P3AT/PCBM blend films, resulting in the acceleration of the crystallization rate, and the decrease of the crystallinity and crystallite size of P3AT. This directly causes the decrease of the open circuit voltage (V_OC) and the increase of both the fill factor (FF) and the short circuit current (J_SC) with the addition of MDBS. Based on the variation of V_OC, FF, and J_SC, the power conversion efficiency (PCE) of P3AT/PCBM BHJ OPV devices improves with the addition of MDBS. Our work verifies that this is a new way to modulate and improve the performance parameters of BHJ OPV devices, i.e., by adding a nucleating agent that modulates the crystallization kinetics of crystalline donor materials.     

Effect of Trace Solvent on the Morphology of P3HT:PCBM Bulk Heterojunction Solar Cells

The performance of bulk‐heterojunction (BHJ) solar cells is strongly correlated with the nanoscale structure of the active layer. Various processing techniques have been explored to improve the nanoscale morphology of the BHJ layer, e.g., by varying the casting solvent, thermal annealing, solvent annealing, and solvent additives. This paper highlights the role of residual solvent in the “dried” BHJ layer, and the effect of residual solvents on PCBM diffusion and ultimately the stability of the morphology. We show that solvent is retained within the BHJ film despite prolonged heat treatment, leading to extensive phase separation, as demonstrated by the growth in the size and quantity of PCBM agglomerates. The addition of a small volume fraction of nitrobenzene to the casting solution inhibits the diffusion of PCBM in the dry film, resulting in smaller PCBM agglomerates, and improves the fill factor of the BHJ device to 0.61 without further tempering. The addition of nitrobenzene also increases the P3HT crystalline content, while increasing the onset temperature for melting of P3HT side chains and backbone. The melting temperature for PCBM is also higher with the nitrobenzene additive present.     

Cover Picture: Tuning the Dimensions of C60‐Based Needlelike Crystals in Blended Thin Films (Adv. Funct. Mater. 6/2006)

A new ordered structure of the C₆₀ derivative PCBM is obtained in thin films based on the blend PCBM:P3HT, as detailed by Swinnen, Manca, and co‐workers on p. 760. Needlelike crystalline PCBM structures, whose dimensions and spatial distribution ca be tuned by adjusting the blend ratio and annealing conditions, are formed. In typical solar‐cell applications of these blended films, these results indicate that during long‐term operation under normal conditions (50–70 °C) morphology changes and a decrease in cell performance could occur. A new ordered structure of the C₆₀ derivative PCBM ([6‐6]‐phenyl C₆₁‐butyric acid methyl ester) is obtained in thin films based on the blend PCBM:regioregular P3HT (poly(3‐hexylthiophene)). Rapid formation of needlelike crystalline PCBM structures of a few micrometers up to 100 μm in size is demonstrated by submitting the blended thin films to an appropriate thermal treatment. These structures can grow out to a 2D network of PCBM needles and, in specific cases, to spectacular PCBM fans. Key parameters to tune the dimensions and spatial distribution of the PCBM needles are blend ratio and annealing conditions. The as‐obtained blended films and crystals are probed using atomic force microscopy, transmission electron microscopy, selected area electron diffraction, optical microscopy, and confocal fluorescence microscopy. Based on the analytical results, the growth mechanism of the PCBM structures within the film is described in terms of diffusion of PCBM towards the PCBM crystals, leaving highly crystalline P3HT behind in the surrounding matrix.     

Effects of Annealing on the Nanomorphology and Performance of Poly(alkylthiophene):Fullerene Bulk‐Heterojunction Solar Cells

The evolution of nanomorphology within thin solid‐state films of poly(3‐alkylthiophene):[6,6]‐phenyl‐C₆₁ butyric acid methyl ester (P3AT:PCBM) blends during the film formation and subsequent thermal annealing is reported. In detail, the influence of the P3AT's alkyl side chain length on the polymer/fullerene phase separation is discussed. Butyl, hexyl, octyl, decyl, and dodecyl side groups are investigated. All of the P3ATs used were regioregular. To elucidate the nanomorphology, atomic force microscopy (AFM), X‐ray diffraction, and optical spectroscopy are applied. Furthermore, photovoltaic devices of each of the different P3ATs have been constructed, characterized, and correlated with the nanostructure of the blends. It is proposed that the thermal‐annealing step, commonly applied to these P3AT:PCBM blend films, controls two main issues at the same time: a) the crystallization of P3AT and b) the phase separation and diffusion of PCBM. The results show that PCBM diffusion is the main limiting process for reaching high device performances.     

Electric-field controlled light-emissive characteristics in nanoscale for polymer/fullerene organic solar cells

Bulk-hetero-junction (BHJ) organic photovoltaic cells (OPVCs) consisting of a poly(3-hexylthiophene) (P3HT) as a donor and [6,6]-phenyl C₆₁ butyric acid methyl ester (PCBM) as an acceptor were fabricated and their light-emissive characteristics as a function of applied bias were investigated. The nanoscale luminescence spectra at different positions on the P3HT/PCBM based photovoltaic cells were measured using a laser confocal microscope (LCM) with a high spatial resolution. For the P3HT/PCBM OPVCs with a relatively thin active layer, the light-emissive characteristics were changed considerably with varying applied bias. We observed that the luminescence intensity increased with increasing reverse bias under light illumination, this result was confirmed by the LCM photoluminescence mapping images. This result originates from the increase of free charges due to the de-trapping effect of trapped charge transfer excitons near the interface, through the external electric-field and incident light.     

Photovoltaic properties of low band gap copolymers based on phenylenevinylene donor and cyanovinylene 4-nitrophenyl acceptor units

Two novel copolymers P1 and P2 having phenylenevinylene donor and cyanovinylene 4-nitrophenyl acceptor units, were synthesized by heck coupling and employed as electron donor along with PCBM or modified PCBM (F) as electron acceptor for the fabrication of bulk heterojunction (BHJ) photovoltaic devices. These copolymers P1 and P2 showed broad band absorption around 640-700 nm and optical band gap of 1.60 eV and 1.72 eV, respectively. The highest occupied molecular orbital (HOMO) and lowest unoccupied molecular orbital (LUMO) estimated from cyclic voltammetry measurement reveals that these values are well suitable for the use of these copolymers as electron donor along with PCBM derivatives as electron acceptor for BHJ active layer. The suitable LUMO off set allows efficient photo-induced charge transfer at the donor/acceptor interfaces in the BHJ photovoltaic device and resulting power conversion efficiency (PCE) of 2.8% and 3.29% for P1 and P2, respectively, when PCBM is used as acceptor. This value has been improved up to 3.52% and 4.36% for the devices based on P1 and P2 when F is used as electron acceptor, instead of PCBM. We have also investigated the effect of solvent annealing on the photovoltaic performance of device based on P1: F and P2: F blends and found that the over all PCE of the devices is 4.36% and 4.88%, respectively. The increase in PCE is mainly due to the improvement in the J_sc, which is due to the increased charge transport in the annealed device as compared to as cast device.     

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.