C61-butyric Acid Methyl Ester Research Articles

Crystallization-Arrested Viscoelastic Phase Separation in Semiconducting Polymer Gels

Through a combination of rheological characterization and temperature-variable imaging methods, a novel gelation pathway in dilute solutions of a semiconducting polymer to achieve interconnected, crystalline networks with hierarchical porosity is reported. Upon rapid cooling, solutions of regioregular poly(3-hexylthiophene) (RR-P3HT) in ortho-dichlorobenzene formed thermoreversible gels. Temperature-variable confocal microscopy revealed cooling-induced structural rearrangement to progress through viscoelastic phase separation. The phase separation process arrested prematurely during the formation of micron-sized solvent-rich "holes" within the RR-P3HT matrix due to intrachain crystallization. Cryogen-based scanning electron microscopy of RR P3HT gels revealed the existence of an interfibrillar network exhibiting nano-sized pores. Remarkably, these networks formed to equal gel strengths when a third component, either small molecule phenyl C61 butyric acid methyl ester (PCBM) or non-crystallizing regiorandom (Rra)-P3HT, was added to the solution. Organic solar cells in which the active layers were deposited from phase-separated solutions displayed 45% higher efficiency compared to reference cells.

Design, synthesis and characterization of 1,8-naphthalimide based fullerene derivative as electron transport material for inverted perovskite solar cells

A new fullerene derivative, PC61BNI, was designed and synthesized in which [6,6]-phenyl C61-butyric acid methyl ester (PC61BM) was modified by replacing the methyl group with 1,8-naphthalimide (NI) to investigate the molecular structure modification effect on perovskite solar cell performance. Inverted perovskite solar cells were fabricated employing PC61BNI as an electron transport material (ETM) and its performance was compared with that of the device fabricated using PC61BM. Optical and electrochemical properties of the PC61BNI were characterized, and how NI substitution affects the solar cells performance was investigated. The photoluminescence quenching experiments confirmed efficient electron injection from perovskite film into PC61BNI layer. The lowest unoccupied molecular orbital (LUMO) energy level of PC61BNI (–3.75 eV) was found to be higher than that of PC61BM (–3.91 eV). The device fabricated with PC61BNI exhibited a power conversion efficiency (PCE) of 10.79% with photocurrent density (Jsc) of 20.23 mA/cm2, open-circuit voltage (Voc) of 1.078 V and fill factor (FF) of 0.497.

Ultra-thick semi-crystalline photoactive donor polymer for efficient indoor organic photovoltaics

An in-depth study on the photovoltaic characteristics under indoor lights, i.e., light-emitting diode (LED), fluorescent lamps, and halogen lamps, was performed with varying the photoactive layer thickness (120–870 nm), by comparing those under 1-sun condition. The semi-crystalline mid-gap photoactive polymer, poly[(2,5-bis(2-hexyldecyloxy)phenylene)-alt-(5,6-difluoro-4,7-di(thiophen-2-yl)benzo[c][1,2,5]thiadiazole)] (PPDT2FBT) and a fullerene derivative, [6,6]-phenyl C71 butyric acid methyl ester (PC70BM) were used as a photoactive layer. In the contrary to the measurements under 1-sun condition, the indoor devices show a clearly different behavior, showing the thickness tolerant short-circuit current density (JSC) and fill factor (FF) values with 280–870 nm thick photoactive layers. The retained JSC and FF values of thick indoor devices were discussed in terms of the parasitic resistance effects based on the single-diode equivalent circuit model. The much lower series/shunt resistance (Rs/RP) ratio was measured with thick photoactive layer (≥280 nm), resulting in negligible decreases in the JSC and FF values even with a 870-nm-thick active layer under the LED condition. Under 1000 lx LED light, the PPDT2FBT:PC70BM device showed an optimum power conversion efficiency (PCE) of 16% (max power density, 44.8 μW/cm2) with an open-circuit voltage of 587 mV, a JSC of 117 μA/cm2, and a FF of 65.2. The device with a 870-nm-thick active layer still exhibited an excellent performance with a PCE of 12.5%. These results clearly suggest that the critical parasitic resistance effects on the performance vary depending on the light illumination condition, and the large RP associated with the viable thick photoactive layer and the well-matched absorption (of photoactive layer) with the irradiance spectrum (of indoor light) are essential to realize efficient indoor photovoltaic cells with high JSC and FF.

Synergistic Effect of Fullerenes on the Laser-Induced Periodic Surface Structuring of Poly(3-Hexyl Thiophene).

Ordered and homogeneous laser-induced periodic surface structures (LIPSS) could be fabricated in poly(3-hexyl thiophene):[6,6]-phenyl C71-butyric acid methyl ester (P3HT:PC71BM) blends by using wavelengths in the ultraviolet (UV) range (266 nm). The absorption coefficient of PC71BM, which is maximum in its UV–Visible absorption spectrum around 266 nm, enhanced the overall absorption of the blend. In addition, PC71BM itself was capable of developing homogeneous LIPSS by laser irradiation at λlaser = 266 nm. Therefore, we proposed that the synergistic effect of PC71BM on the LIPSS formation in P3HT:PC71BM (1:1) was due to a templating effect for the LIPSS formation of the PC71BM itself, which added to the overall increment of the absorption of the blend. LIPSS formation at ambient conditions in this wavelength range led to chemical modification of both P3HT and PC71BM, which rendered to non-conducting samples. Irradiation in vacuum significantly reduced radiation damage, rendering to the characteristic electrical conductivity pattern observed in P3HT LIPSS samples irradiated in the visible range. This effect could be of potential interest in order to obtain LIPSS in low absorbing polymers.

Functional nanostructured surfaces induced by laser on fullerene thin films

We report a method to produce nanosecond pulsed laser induced periodic surface structures (LIPSS) on spin-coated [6,6]‑phenyl C71-butyric acid methyl ester (PC71BM) films exhibiting a photoinduced resist-free imprinting (PRI) property. LIPSS in PC71BM are resist free and can be solvent developed, under certain conditions, leaving the laser illuminated zone as an undissolved residue. LIPSS prepared with a wavelength of 532 nm selectively preserve the electrical conductivity on the LIPSS valleys. The heterogeneous conducting pattern consisting in conducting valleys and less conducting hills observed in the LIPSS has been interpreted as due to a reduction in the crystallinity of the hills provoked by the fast heating/cooling process induced by every laser pulse. On the basis of the experiments we propose that irradiated PC71BM films: i) suffer a fast heating/cooling process tending to reduce the overall crystallinity of the LIPSS and therefore decreasing the electrical conductivity of the hills while leaving a remnant conducting film underneath the hills, ii) during laser irradiation the sample suffers a heat treatment leading to the development of a buried phase with enhanced crystallinity, close to the silicon substrate, formed by larger crystals with enhanced electrical conductivity and iii) further solvent treatment reveals the buried phase which remains in the form of partially electrically conducting nanowires. These results point towards the potential use of the described technology for nanofabrication of organic electronic devices.

Ternary Composites with PbS Quantum Dots for Hybrid Photovoltaics

Ternary hybrid photovoltaics based on polymers, fullerenes, and colloidal semiconductor quantum dots (QDs) bring together high efficiency and technological flexibility. To increase the performance of such hybrid solar cells, a thorough control over both film morphology and charge transport is required. In the present work, the morphology and optical properties of films of binary and ternary blends of PbS QDs with poly(3-hexylthiophene-2,5diyl) and [6,6]-phenyl C71 butyric acid methyl ester have been investigated by steady-state and time-resolved photoluminescence spectroscopy, atomic force microscopy, and confocal laser-scanning microscopy. The influence of postdeposition and liquid-phase ligand exchange procedures on film properties has been considered. It is shown that the liquid-phase iodide passivation improves both film quality and charge-transfer efficiency. The mixture of three components facilitates charge transfer in the hybrid material, but a thorough control over QD size and ligand type is requ...

Förster resonance energy transfer and morphology optimization for high-performance ternary organic photodetectors

Abstract Aiming at extending the photoresponse range of the photodetectors based on Poly(3-hexylthiophene-2,5-diyl): [6,6]-Phenyl C71 butyric acid methyl ester (P3HT: PCBM) host system, Poly [(5,6-difluoro-2,1,3-benzothiadiazole-4,7-diyl)-alt-(3,3‴-di(2-octyldodecyl)-2,2’;5’,2’’;5’’,2‴-quaterthiophen-5,5‴-diyl)] (PffBT4T-2OD) with wide spectral response range, proper energy levels and high crystallinity was integrated to fabricate ternary organic photodetectors. The PffBT4T-2OD introduces energy cascade and Forster resonance energy transfer (FRET) effect from P3HT to PffBT4T-2OD, which contributes to the photocurrent generation. Furthermore, PffBT4T-2OD creates films with desirable crystallinity to produce a favorable morphology resulting in the apparent d-spacing decrement of π-π stacking of P3HT: PCBM, which probably increases the intermolecular charge hopping efficiency. The optimal photodetector shows high on/off ratio of 6.7 × 104 with a broad spectral response from 300 nm to 800 nm via incorporating 15 wt% PffBT4T-2OD into polymer bulk heterojunction, which is an obvious improvement compared with the 2.6 × 104 on/off ratio of P3HT: PCBM. This work indicates that FRET and morphology optimization have a profound effect on photoresponse and electrical properties of organic photodetectors.

Flexible All-Organic Photorefractive Devices

The objective of the present study is to demonstrate and evaluate the photorefractive (PR) performance of an all-organic PR device with a self-assembled monolayer (SAM)-modified organic conductive electrode of PEDOT:PSS coated on polyethylene terephthalate (PET). The PR composite consisted of a triphenylamine-based photoconductive polymer: poly(4-(diphenylamino)benzyl acrylate) (PDAA), a triphenylamine photoconductive plasticizer: (4-(diphenylamino)phenyl)methanol (TPAOH), a nonlinear optical dye based on aminocyanostyrene: (4-asacycloheptylbenzylidenemalononitrile) (7-DCST), and soluble fullerene: [6,6]-phenyl C61 butyric acid-methyl ester (PCBM). For comparison with the all-organic PR device, the PR performances using PET/ITO, glass/ITO, and glass/PEDOT:PSS substrates were also evaluated. At an applied electric field of 40 V μm–1, the diffraction efficiency and the response time of the PR device using the PET/PEDOT:PSS-SAM substrate were 21.9%, and 390 ms, respectively. As a result of repeating bending ...

Effects of DIO on the charge recombination behaviors of PTB7:PC71BM photovoltaics

Abstract The influence of the solvent additive 1, 8-diiodooctane (DIO) on the charge carrier recombination behaviours of poly[[4,8-bis[(2-ethylhexyl)oxy]benzo [1,2-b:4,5-b0] dithiophene-2,6-diyl][3-fluoro-2-[(2-ethylhexyl)carbonyl]thieno[3,4-b] thiophenediy1]] (PTB7): phenyl-[6, 6]-C71-butyric acid methyl ester(PC71BM) organic photovoltaics (OPVs) was investigated. The measurement of transient photocurrent (TPC) implies that the devices processed with 3% DIO have less charge carrier recombination loss than the devices without DIO. The photo-induced charge extraction by linearly increasing voltage (photo-CELIV) technique shows that the device with DIO has less charge carrier trap population and thus the bimolecular recombination can be reduced. The modified Onsager–Braun model with bimolecular recombination rate γ b i , calculated from the photo-CELIV, indicated that by adding DIO, the binding energy of the charge-transfer exciton at the interface of PTB7 and PC71BM reduced, thus the geminate recombination loss decreased. Atomic Force Microscope (AFM) images show that DIO can optimize the morphology of the active layer, which is beneficial to the exciton dissociation and the reduction of the charge carriers trapping. The reduction of the charge carrier recombination including geminate recombination and non-geminate recombination lead to the large increase of current density (JSC), fill factor (FF), and power conversion efficiency (PCE) of PTB7:PC71BM OPVs.

Doping induced performance enhancement in inverted small molecule organic photodiodes operating below 1V reverse bias - Towards compatibility with CMOS for imaging applications

Abstract Organic photodiodes (OPDs) offer a myriad of advantages over conventional inorganic photodetectors, making them particularly attractive for imaging application. One of the key challenges preventing their utilization is the need for their integration into the standard CMOS processing. Herein, we report a CMOS-compatible top-illuminated inverted small molecule bi-layer OPD with extremely low dark leakage current. The device utilizes a titanium nitride (TiN) bottom electrode modified by a [6,6]-phenyl C61 butyric acid methyl ester (PCBM) cathode buffer layer (CBL). We systemetically show that doping the CBL enhances device's low voltage (below 1 V reverse bias) photoresponse by increasing the linear dynamic range (LDR) and making the bandwidth of the photodidoe broader without compromising the leakage current. The optimized device exhibits a dark leakage current of only ∼6 × 10−10 A/cm2 at −0.5 V. The external quantum efficiency (EQE) at 500 nm reaches 23% with a calculated specific detectivity as high as 7.15 × 1012 cm Hz1/2/W (Jones). Also the LDR approaches 140 dB and the bandwidth is about 400 kHz, at −0.5 V bias. The proposed device structure is fully compatible with CMOS processing and can be integrated onto a CMOS readout circuit offering the potential to be applied in high-performance large-scale imaging arrays.

Stability and Reliability of PTB7:PC71BM and PTB7:PC61BM Inverted Organic Solar Cells: A Comparative Study

Blends of poly[[4,8-bis[(2-ethylhexyl)oxy]benzo[1,2-b:4,5-b']dithiophene-2,6-diyl][3-fluoro-2-[(2-ethylhexyl)carbonyl]thieno[3,4-b]thiophenediyl]] (PTB7) molecule with [6,6]-phenyl C71-butyric acid methyl ester (PC71BM) and, sometimes, with [6,6]-phenyl C61-butyric acid methyl ester (PC61BM) are popular for the fabrication of organic solar cell devices with efficiencies greater than 7% in many laboratories around the world. However, these devices have a poor lifetime, even in comparison with many other organic active layer solar cells. In this paper, PTB7:PC71BM and PTB7:PC61BM active layer devices fabricated in a stable process line have been systematically studied to understand the device degradation processes. The studies show that PTB7:PC61BM devices have a longer shelf-life in comparison with PTB7:PC71BM devices, with a median T80 (time for the efficiency to decrease to 80% of the pristine device) of 50 and 11 days, respectively. The lifetimes of both these devices when exposed to outdoor sunlight, however, are very low (median T80 of about 6 h). Time analyses of device photovoltaic parameters, dark current–voltage characteristics, and the spectra of external quantum efficiencies help get an insight into the reasons for device degradation. The shelf-life degradation process is dominated by trap formation and charge extraction limitations. Light-exposure degradation is dominated by lower light absorption because of material degradation in the device active layer. These results should help in the design of more stable and improved PTB7-based devices.

Effect of Thickness and Composition Ratio of Poly(3-Hexylthiophene) and [6,6]-Phenyl C60-Butyric Acid Methyl Ester Thin Film on Optical Absorption for Organic Solar Cell Fabrication

A Blend of poly(3-hexylthiophene) (P3HT) and [6,6]-phenyl C60-butyric acid methyl ester (PCBM), a fullerene derivate based donor-acceptor copolymer, is one of the widely used organic solar cell materials for photon-electron conversion. Thin films were developed, characterized, and optimized for optical absorbance. Absorption spectra were measured using a UV-VIS spectrophotometer. In this work, the effects of composition ratios of P3HT:PC₆₀BM and various thicknesses was studied in ambient conditions. The P3HT:PC₆₁BM thin film was deposited in two different composition ratio (1:1 and 1:3) and fabricated at seven different thicknesses of 20 nm, 30 nm, 35 nm, 87 nm, 98 nm, 115 nm, and 146 nm corresponding to spin coating speeds of 4000rpm, 3000rpm, 2000rpm, 1500rpm, 1250rpm, 1000rpm, and 750rpm, respectively. P3HT:PC₆₀BM thin film composition ratio of 1:1 with thickness of 87nm shows relatively better photon absorption optical parameter than P3HT:PC₆₀BM composition ratio of 1:3. P3HT: PC₆₁BM solution coated at a spin speed of 1500 rpm shows a better absorption of photon energy. The results showed that the optimum thickness of the thin film is 87 nm at composition ratio of 1:1. Energy band gap values of composition ratio of 1:3 is observed to decreases with increase in spin- speed from 3.9 eV to 3.7 eV. The results can be used as a guideline for improving the design and fabrication of active layer of organic solar cells.

Composition-Morphology Correlation in PTB7-Th/PC71BM Blend Films for Organic Solar Cells.

From a morphological perspective, the understanding of the influence of the [6,6]-phenyl C71-butyric acid methyl ester (PC71BM) content on the morphology of the active layer is not complete in organic solar cells (OSCs) with bulk heterojunction (BHJ) configuration based on the low-bandgap polymer poly[4,8-bis(5-(2-ethylhexyl)thiophen-2-yl)benzo[1,2- b;4,5- b']dithiophene-2,6-diyl- alt-(4-(2-ethylhexyl)-3-fluorothieno[3,4- b]thiophene-)-2-carboxylate-2-6-diyl] (PTB7-Th). In this work, we obtain the highest power conversion efficiency (PCE) of 10.5% for BHJ organic solar cells (OSCs) with a PTB7-Th/PC71BM weight ratio of 1:1.5. To understand the differences in PCEs caused by the PC71BM content, we investigate the morphology of PTB7-Th/PC71BM blend films in detail by determining the domain sizes, the polymer crystal structure, optical properties, and vertical composition as a function of the PC71BM concentration. The surface morphology is examined with atomic force microscopy, and the inner film morphology is probed with grazing incidence small-angle X-ray scattering. The PTB7-Th crystal structure is characterized with grazing incidence wide-angle X-ray scattering and UV/vis spectroscopy. X-ray reflectivity is employed to yield information about the film vertical composition. The results show that in PTB7-Th/PC71BM blend films, the increase of PC71BM content leads to an enhanced microphase separation and a decreased polymer crystallinity. Moreover, a high PC71BM concentration is found to decrease the polymer domain sizes and crystal sizes and to promote polymer conjugation length and formation of fullerene-rich and/or polymer-rich layers. The differences in photovoltaic performance are well explained by these findings.

Elucidating the impact of N-arylanilino substituents of squaraines on their photovoltaic performances

Abstract Squaraines have attracted increasing research attention for organic photovoltaic applications because of their facile and low-cost synthesis, and intense and broad absorption in the visible and near-infrared (Vis-NIR) regions. Herein, three new squaraines, N-phenylanilino substituted SQ-EP, N-2-naphthylanilino substituted SQ-EN, and N-fluorenylanilino substituted SQ-EF, were developed for improving the hole mobility of aniline-based squaraines. The substitution effect of N-arylanilino groups on the optoelectronic properties of squaraines was investigated. These squaraines exhibited similar absorbance spectra, HOMO (highest occupied molecular orbital) and LUMO (lowest unoccupied molecular orbital) energy levels, and hole mobilities in their neat films. However, compared to their neat films, the hole mobility of the SQ-EP-based BHJ blend film showed the smallest decrease when blending with PC71BM ([6,6]-phenyl C71 butyric acid methyl ester). Besides, morphological studies have shown that a phase separation of 20–30 nm can only be observed in the SQ-EP/PC71BM blend film. Consequently, a solution-processed bulk-heterojunction (BHJ) organic photovoltaic (OPV) device fabricated with the as-cast SQ-EP/PC71BM blend film exhibited obviously higher power conversion efficiency (PCE: 5.4%) than those of the SQ-EN/PC71BM (PCE: 4.3%) or SQ-EF/PC71BM systems (PCE: 2.8%). This is one of the highest recorded PCE values in aniline-based squaraines single-junction BHJ-OPV devices. This much-enhanced PCE can be attributed to the significant increases in short-circuit current density (Jsc) and fill factor (FF) of the SQ-EP/PC71BM-based OPV device.

Facile Synthetic Route of a Solution-Processable, Thieno[3,4-c]pyrrolo-4,6-dione-Based Conjugated Small Molecule and Control of the Optoelectronic Properties via Processing Additives

In this study, a new type of low-bandgap small molecule has been synthesized with a thieno[3,4-c]pyrrole-4,6-dione (TPD) derivative for application in bulk heterojunction (BJH) solar cells. The series of solar cells were fabricated by blending the TPD-based small molecule (M1) and [6,6]-phenyl C71 butyric acid methyl ester (PC71BM). In order to optimize the performance of solar cells, the nanoscale morphologies of the BHJ layers were controlled via processing additives with 1,8-diiodooctane (DIO) and 1-chloronaphthalene (CN). Therefore, we demonstrated that the use of CN successively suppressed molecular aggregation and demonstrated suitable phase separation, in addition to increasing the power conversion efficiency from 0.36% to 1.86%.

A study about lifetime of photovoltaic fibers

In this study, the stability of polymer-based photovoltaic fibers was investigated in ambient and inert atmosphere. Photovoltaic (PV) fibers, similarly produced by using both polymer blend of wide and low bandgap polymers (P3HT: PTB7: PCDTBT) and only wide bandgap (P3HT) polymer with [6,6]-phenyl C61 butyric acid methyl ester (PCBM) in active layer were measured in ambient and in inert environment after dark storage, and then, their photovoltaic performances and stabilities were compared. Maximum power conversion efficiency of 2.01% was obtained from photovoltaic fiber with P3HT: PTB7: PCDTBT polymer blend. When stability results were considered, at end of 7th day, photovoltaic fibers having P3HT: PTB7: PCDTBT:PCBM active layer showed better performance than P3HT: PCBM-based PV fibers.

Enhanced Detectivity and Suppressed Dark Current of Perovskite-InGaZnO Phototransistor via a PCBM Interlayer.

Hybrid phototransistors based on InGaZnO (IGZO) metal oxide thin-film transistors (TFT) and a photoabsorbing capping layer such as perovskite (MAPbI3) are a promising low-cost device for developing advanced X-ray and UV flat-panel imagers. However, it is found that the introduction of MAPbI3 inevitably damages the IGZO channel layer during fabrication, leading to deteriorated TFT characteristics such as off-current rising and threshold voltage shift. Here, we report an effective approach for improving the performance of the perovskite-IGZO phototransistor by inserting a [6,6]-phenyl C61-butyric acid methyl ester (PCBM) or PCBM:PMMA interlayer between the patterned MAPbI3 and IGZO. The interlayer effectively prevents the IGZO from damage by the perovskite fabrication process, while allowing efficient charge transfer for photosensing. In this configuration, we have achieved a high-detectivity (1.35 × 1012 Jones) perovskite-IGZO phototransistor with suppressed off-state drain current (∼10 pA) in the dark. This work points out the importance of interface engineering for realizing higher performance and reliable heterogeneous phototransistors.

Spin-dependent recombination of the charge-transfer state in photovoltaic polymer/fullerene blends

ABSTRACTQ-band electron spin echo (ESE) spectroscopy was applied for studying the spin-dependent recombination of charge transfer (CT) states in the benchmark organic photovoltaics (OPV) blend of poly(3-hexylthiophene-2,5-diyl) and [6,6]-phenyl C61 butyric acid methyl ester (P3HT/PC60BM). Selective microwave excitation and a special protocol for ESE data treatment allowed to suppress the ESE signal of thermalised polarons and weakly coupled CT states and to address CT states with a relatively short distance between positive and negative polarons (1.5 nm < r < 2.5 nm). Inversion of the in-phase ESE signal with increase of the delay after laser flash was observed for the regioregular P3HT•+/PC60BM•− CT state at a temperature of 40 K. This effect is very similar to the inversion of the time resolved (TR) EPR spectrum of the same system obtained previously. Both effects can be explained by spin-dependent recombination of the CT state, with the recombination via the triplet channel proceeding much slower than via the singlet channel. For the regiorandom P3HT•+/PC60BM•− CT state no ESE sign inversion was observed in an analogous experiment. The result suggests the importance of CT state formation via a triplet exciton, a process which was not considered previously for the P3HT/PC60BM blend.

A method to discern voltage dependent internal photoemission component from photoconductivity content in spectral response of metal-organic semiconductor-metal devices and evaluate the interface barriers

Abstract The ability to detect and determine a typically weak internal photoemission (IPE) signal from a usually strong photoconductivity (PC) signal within a spectral response (SR) measurement can be helpful in studying the interface properties of metal-semiconductor junctions, which are often critical for proper design and analysis of semiconductor electronic devices including organic photovoltaic devices. In this report, we propose a method to discern the voltage dependent IPE component from PC content in a measured SR of organic devices. The method is based on the ratio of SR measured at different voltage bias conditions in metal-organic semiconductor-metal devices. The separated IPE component, hence, can be used to estimate the associated interface barrier(s). The differentiation between IPE and PC is probably caused due to the barrier changing at the metal and organic semiconductor interface on the application of bias which causes a modulation in IPE signal with the applied bias. In this work, a theoretical basis for the method of characterisation has been developed. Based on the analysis, as an example, the barriers between [6,6] phenyl C61 butyric acid methyl ester (PCBM) and electrodes indium tin oxide and aluminium for different bias voltages have been evaluated. This simple and elegant method of studying metal and organic semiconductor barrier, when applicable, can be helpful in device design and characterisation.

Optimizing nanoscale morphology and improving carrier transport of PCDTBT-PCBM bulk heterojunction by cyclic carboxylate nucleating agents

Abstract In this work, four cyclic carboxylate commercial nucleating agents, bicyclo [2.2.1] heptane-2,3-dicarboxylic acid disodium salt (HPN-68L), sodium salt of hexahydrophthalic acid (HHPA-Na), sodium benzoate (Be-Na) and calcium salt of hexahydrophthalic acid (HPN-20E) were respectively added into poly[N-9′-heptadecanyl-2,7-carbazole-alt-5,5-(4′,7′-di-2-thienyl-2′,1′,3′ benzothiadi-azole)] (PCDTBT)-[6,6]-phenyl C61-butyric acid methyl ester (PCBM) blend. Atomic force microscopy (AFM) and UV–vis measurements indicate that the addition of carboxylic acid sodium salts can effectively optimize the morphology of active layer, decrease the phase domain size and increase the optical absorption intensity of PCDTBT-PCBM blends. The PCDTBT-PCBM-additive ternary devices were fabricated and found that adding carboxylic acid sodium salts can improve the hole mobility, balance the hole and electron mobility and finally increase the power conversion efficiency (PCE). Fixed the additive content as 5%, the modulation ability of the bicyclic dicarboxylic acid sodium salt HPN-68L is best, monocyclic dicarboxylic acid sodium salt HHPA-Na comes second, monocyclic carboxylic acid sodium salt Be-Na is worst. The addition of carboxylic acid calcium salt HPN-20E has no effects on the morphology and optical absorption intensity of the PCDTBT-PCBM blend, and the photoelectric properties of PCDTBT-PCBM-HPN-20E ternary device decreases in comparison with those of pristine PCDTBT-PCBM binary device. The modulation ability of cyclic carboxylate is related to its surface free energy and its location in the PCDTBT-PCBM blend. HPN-68L locates in the interfacial region between PCDTBT and PCBM, other cyclic carboxylates locates in the PCBM. Our finding suggests the addition of cyclic carboxylic acid sodium salts can be a facile approach to optimize the morphology and increase the electrical properties of organic materials for future development of organic photovoltaic devices.