Phenyl C61-butyric Acid Methyl Research Articles

Unraveling the unstable amorphous phase evolution effect on burn-in loss in polymer-fullerene solar cells

Abstract The performance degradation of organic photovoltaics is one of the main limitations to their commercialization, especially an initial, rapid degradation-period, termed as a burn-in loss. Herein, we demonstrate that burn-in loss is caused by the presence of thermodynamically unstable mixed-amorphous phase in the active layer. By using a combination of grazing incidence small angle X-ray scattering and photophysical process experiments, we observe that [6,6]-Phenyl C61 butyric acid methyl ester (PC61BM) molecules rapidly move from the finely-mixed amorphous regimes into crystalline or ordered regimes under accelerated conditions (ISOS-D-2 protocol), resulting in a fast short circuit current (Jsc) burn-in loss. Following an ultraviolet radiation (UV) light processing to control amorphous phase, the kinetics of thermally induced PC61BM crystallization can be slowed down due to the formation of the photo-induced PC61BM dimers in the active layer leading to a smaller burn-in loss. In the case of UV irradiated films, even if the molecules migrated out of amorphous phase, the PC61BM-rich phase becomes loose, rather than the compact and sphere-shaped aggregation, which has been observed in pristine films. These analyses reveal the evolution of thermodynamically unstable amorphous phases eventually leading to a decline power conversion efficiency within a short period of time. The results provide a further design basis of organic photovoltaic materials with good thermal stability and high efficient simultaneously.

Visible to Near‐Infrared‐Absorbing Polymers Containing Bithiazole and 2,3‐Didodecyl‐6,7‐Difluoroquinoxaline Derivatives for Polymer Solar Cells

Electron donor and electron acceptor materials for solution‐processable polymer solar cells (PSCs) should ideally exhibit a narrow band gap (Eg) and high solubility for improved performance. Herein, we synthesized two new near‐infrared‐absorbing alternating polymers, namely P(BTz‐FQ) and P(BTz‐DTFQ), via Stille polymerization of 4‐butoxy‐5‐(4‐butoxy‐2‐(trimethylstannyl)thiazol‐5‐yl)‐2‐(trimethylstannyl)thiazole and 5,8‐dibromo‐2,3‐didodecyl‐6,7‐difluoroquinoxaline or 5,8‐bis(5‐bromothiophen‐2‐yl)‐2,3‐didodecyl‐6,7‐difluoroquinoxaline. The absorption spectra of P(BTz‐FQ) and P(BTz‐DTFQ) ranged from 300 to 900 nm with two distinct absorption maxima at 718 and 800 nm and 665 and 718 nm, respectively. Both polymers exhibited an identical Eg of 1.41 eV, which is the lowest value reported for quinoxaline‐based polymers to date. Their highest occupied (−5.04 and −5.09 eV) and lowest unoccupied (−3.63 and −3.68 eV) molecular orbital levels were suitable for their use as electron donors along with the fullerene derivative, [6,6]‐phenyl C71 butyric acid methyl ester, as the electron acceptor in PSCs. The maximum power conversion efficiencies obtained for the PSCs utilizing P(BTz‐FQ) and P(BTz‐DTFQ) were 0.51% and 0.71%, respectively. These findings demonstrate that thiazole and fluoroquinoxaline derivatives are promising materials for PSCs and other optoelectronic devices.

Effects of Interfacial Layers on the Open Circuit Voltage of Polymer/Fullerene Bulk Heterojunction Devices Studied by Charge Extraction Techniques.

Interfacial layers are frequently used in organic solar cells performing various functions, including blocking surface recombination, improving selectivity of charge carrier extraction, modification of the work function of the contact materials, and enhancing light absorption within the photoactive layer through an optical cavity effect. The aim of this work is to investigate the origin of performance enhancement of bulk heterojunction solar cells using various electron and hole interfacial layers, with a particular focus on separating the contributions of work function modification and reduced recombination to the improvement of the open circuit voltage ( Voc). Solar cells using poly[ N-9'-hepta-decanyl-2,7-carbazole- alt-5,5-(4',7'-di-2-thienyl-2',1',3'-benzothiadiazole)]:[6,6]-phenyl C70-butyric acid methyl ester (1:4) active layers were prepared with a combination of polymeric, metal oxide, and polyelectrolyte electron and/or hole interfacial layers. Four device structures with (i) no interfacial layers (reference); (ii) only hole; (iii) only electron; (iv) both electron and hole interfacial layers were fabricated and compared using current-voltage, transient photovoltage, and charge extraction measurements. The voltage gains (Δ Voc) at matched charge density attributed to work function modification (Δ Voch or Δ Voce) are distinguished from the increase in Voc arising from increased charge carrier density. At the hole contact, Δ Voch was 0.21 V by using a poly(3,4-ethylenedioxythiophene):poly(styrenesulfonate) hole interfacial layer, whereas Δ Voce was 0.29 V on the electron contact using a polyethoxylate imine-TiO x interfacial layer compared to reference devices. The electron lifetime also improved by orders of magnitude with the use of either electron or hole contact layers, contributing to a further 0.35-0.38 V increase in the open circuit voltage (Δ Vocrec) because of increased charge density. The increased charge carrier lifetime is proposed to originate from the larger spatial separation of the electrons and holes in the device because of the increased internal field. Using both an electron and a hole interfacial layer did not significantly increase the charge carrier lifetime compared to single interfacial layer devices; therefore, the Voc did not increase significantly. The findings presented clarify the role of interfacial layers in organic solar cells and provide new insights into using time-resolved charge extraction techniques to understand the influence of interfacial layers on the open circuit voltage.

Improved stability and performance of organic photovoltaic cells by application of carbon nanostructures and PEDOT:PSS composites as additional transparent electrodes

Conventional bulk heterojunction organic photovoltaic cell (OPVC) with regioregular poly[3-hexylthiophene-2,5-diyl] (P3HT): [6,6]-phenyl C61 butyric acid methyl ester (PCBM) blend as active layer has been fabricated with simple ITO/P3HT:PCBM/Al structure and its performance is compared with that of OPVC fabricated by incorporating an additional conducting layer of poly(3,4-ethylenedioxythiophene)-poly(styrenesulfonate) (PEDOT:PSS) in between the active layer and ITO. An improvement of power conversion efficiency (PCE) has been observed from 2.716% to 2.733% due to the incorporation of PEDOT:PSS. The PCE has been further enhanced by replacing PEDOT:PSS with composites of carbon nanotubes (CNTs)/PEDOT:PSS and reduced graphene oxide (RGO)/PEDOT:PSS which have been prepared by simple solution method and the device parameters of all OPVCs are collated. A maximum PCE of 2.823% with corresponding short-circuit current density (Jsc) of 9.858 mA/cm2, open-circuit voltage (Voc) of 646.923 mV, and a fill factor (FF) of 44.263% has been achieved (at 25 °C) for the device with 5 wt% of CNTs in PEDOT:PSS. The performances of all fabricated OPVCs have been compared at different temperatures (25 °C, 30 °C, and 35 °C) and a declination in PCE is noted with increase in temperature. The stability of selected devices exposed to open atmosphere has been checked by measuring their parameters at different time intervals and it is observed that the degradation of materials reduces the performance of OPVCs. Under all different circumstances, OPVCs fabricated using the composites have been observed to perform better along with significant enhancement in PCE compared to OPVCs fabricated without using the composites.

Thin metal top electrode and interface engineering for efficient and air-stable semitransparent perovskite solar cells

To find promising device architecture for air-stable as well as efficient semitransparent perovskite solar cells (PeSCs), Ag & Cu semitransparent top electrode and interfacial engineering technologies are explored in PeSCs consisting with indium tin oxide (ITO)/hole transporting layer (HTL)/CH3NH3PbI3/[6,6]-phenyl-C61 butyric acid methyl ester (PCBM)/Ag or Cu. Devices with NiOx HTL exhibits better performance than conventional poly (3,4-ethylenedioxythiophene) polystyrene sulfonate (PEDOT:PSS) based devices and modification of PCBM with polyethylenimine ethoxylated (PEIE) also induces improved performance. Optimized semitransparent PeSC with Cu shows superior performance, achieving a power conversion efficiency (PCE) of 11.95% and average visible transmittance (AVT) of ∼20%, and stability to Ag based device.

Stable Efficiency Exceeding 20.6% for Inverted Perovskite Solar Cells through Polymer-Optimized PCBM Electron-Transport Layers.

Fullerene derivative, such as [6,6]-phenyl C61 butyric acid methyl ester (PCBM), is widely used as an electron-transport layer (ETL) in inverted perovskite solar cell (PSC). However, its low electron mobility, complexity in achieving quality film formation, and severe nonradiative recombination at perovskite/PCBM interface due to the large electron capture region, lead tolower efficiency for inverted PSCs compared to the normal structures. Herein, we demonstrate an effective and practical strategy to overcome these challenges. Conjugated n-type polymeric materials are mixed together with PCBM to form a homogeneous bulk-mixed (HBM) continuous film with high electron mobility and suitable energy level. HBM film is found to completely cap the perovskite surface to enhance the electron extraction. The critical electron capture radius of the HBM decreases to 12.52 nm from 14.89 nm of PCBM due to the large relative permittivity, resulting in reduced nonradiative recombination at perovskite/HBM interface. The efficiency of inverted PSCs with HBM ETLs exceeds 20.6% with a high fill factor of 0.82. Further, the stability of devices is improved owing to the high hydrophobicity of the HBM ETLs. Under ambient air condition after 45 days, the efficiency of inverted PSCs based on HBM remains 80% of the initial value. This is significantly higher than the control devices which retain only 48% of the initial value under similar aging conditions. We believe these breakthroughs in improving efficiency and stability of inverted PSCs will expedite their transition.

High-Performance Organic Phototransistors With Vertical Structure Design

In this paper, a novel vertical phototransistor was reported and compared with planar phototransistors for the first time. As compared with the planar phototransistors, the vertical ones exhibited much better photoelectric performance, which is attributed to an ultrashort photo-generated holes transfer distance and a stronger excitons dissociating electrical field due to their ultrashort channel length (tens of nanometers). Moreover, in order to examine the transport and trapping of different carrier charges separately, the impact of [6,6]-phenyl C61-butyric acid methyl ester (PCBM) dopant on the performance of planar and vertical phototransistors was investigated. The vertical devices exhibited an ultrahigh responsivity (~6600 A/W) as well as an excellent detectivity ( $\sim 7\times 10^{15}~\text{Jones}$ ) and a fast photoresponse (rise time of 0.28 s), whereas slight changes were observed in the planar ones with doping of PCBM. The high performance of the blend vertical phototransistors is due to the trapping of the photo-generated electrons with PCBM and the effective transport of holes due to the ultrashort channel length. This paper provided a promising pathway for low-cost, high-performance phototransistors.

Critical Role of Polystyrene Layer on Plasmonic Silver Nanoplates in Organic Photovoltaics

Plasmonic nanoparticles create large local electric field enhancements in organic photovoltaics (OPVs), substantially enhance the absorption of light, and consequently improve the device efficiency. In this report, anisotropic Ag nanoplates (AgNPs) were functionalized by thiol-terminated polystyrene (PS-SH) to yield polystyrene-functionalized Ag nanoplates (PS-AgNPs). The PS-AgNPs were spin-coated directly on the OPV active layer, poly(3-hexylthiophene-2,5-diyl):[6,6]-phenyl C61 butyric acid methyl ester (P3HT:PCBM). A systematic variation of the PS-AgNP solution concentration correlated to different nanoparticle densities on the active layer. The localized surface plasmon resonance (LSPR) of the PS-AgNPs enhanced the light absorption of the active layer, which directly contributed to an increase in exciton yield, demonstrated by the increased photoluminescence emission intensities in P3HT films. In addition, incorporation of the PS-AgNPs decreased the series resistance and increased the photocurrent of the devices. In devices with PS-AgNP at a concentration of 0.57 nM, the power conversion efficiency was 32% higher than the devices without the PS-AgNPs. Without the polystyrene functionalization, however, the AgNPs severely deteriorated the performance of the OPV devices regardless of the nanoparticle concentration.

Synthesis of peripherally tetra substituted neutral azophenoxy zinc phthalocyanine and its application in bulk hetero junction solar cells

Neutral zinc phthalocyanine bearing 4-phenylazopohenoxy group at the periphery (ZnPc-4) has been synthesized from zinc acetate dihydrate Zn(CH3COO)2·2H2O and 4-(phenylazophenoxy)phthalonitrile. The synthesized zinc phthalocyanine ZnPc-4 was characterized using UV–visible, FTIR, 1H NMR and MALDI-TOF mass spectral measurements. Solution processed bulk hetero junction solar cells were fabricated using ZnPc-4 as the donor material and [6,6]-Phenyl C61 butyric acid methyl ester (PCBM) as the acceptor material. A power conversion efficiency of 0.69% was achieved by optimizing the donor:acceptor weight ratio. Variation in device performance with the donor:acceptor weight ratio was investigated using atomic force microscopy.

Syntheses and optical, electrochemical, and photovoltaic properties of polymers with 6‐(2‐thienyl)‐4H‐thieno[2,3‐b]indole with a variety of electron‐deficient units

ABSTRACTConjugated polymers were synthesized and used for polymer solar cells with new electron‐rich units, 6‐(2‐thienyl)‐4H‐thieno[2,3‐b]indole (2‐TTI). 2‐TTI was coupled with electron‐pulling units, including benzothiadiazole and benzimidazole derivatives, to provide push–pull types of conjugated polymers (poly(8‐(heptadecan‐9‐yl)‐6‐(thiophen‐2‐yl)‐8H‐thieno[2,3‐b]indole)‐alt‐(2‐methyl‐5,6‐bis(octyloxy)‐4,7‐di(thiophen‐2‐yl)‐2‐(trifluoromethyl)‐2H‐benzimidazole) (PTTIDOCF3), poly(8‐(heptadecan‐9‐yl)‐6‐(thiophen‐2‐yl)‐8H‐thieno[2,3‐b]indole)‐alt‐(5,6‐bis(octyloxy)‐4,7‐di(thiophen‐2‐yl)‐2,1,3‐benzothiadiazole) (PTTIDOBT), poly(8‐(heptadecan‐9‐yl)‐6‐(thiophen‐2‐yl)‐8H‐thieno[2,3‐b]indole)‐alt‐(2,2‐dimethyl‐4,7‐di(thiophen‐2‐yl)‐2H‐benzimidazole) (PTTIMBI), and poly(8‐(heptadecan‐9‐yl)‐6‐(thiophen‐2‐yl)‐8H‐thieno[2,3‐b]indole)‐alt‐(2,2‐dimethyl‐5,6‐bis(octyloxy)‐4,7‐di(thiophen‐2‐yl)‐2H‐benzimidazole) (PTTIDOMBI)). The synthesized conjugated polymers provided deep highest occupied molecular orbital energy levels for higher open‐circuit voltages (VOC). The device composed of PTTIDOMBI and [6,6]‐Phenyl C71 butyric acid methyl ester PC71BM (1:2) with chloronaphthalene additive showed a VOC of 0.72 V, a short‐circuit current (JSC) of 9.16 mA/cm2, and a fill factor of 0.43; this gave a power conversion efficiency (PCE) of 2.84%. The PTTIDOMBI provided better morphology for enhanced charge transport, and this led to the higher JSC and PCE of the organic solar cells. © 2019 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2019, 136, 47624.

Fabrication and characterization of inverted organic PTB7:PC70BM solar cells using Hf-In-ZnO as electron transport layer

In this study, we report the use of Hafnium-Indium-Zinc-Oxide (HIZO) as electron transport layer (ETL) in inverted organic solar cells (iOSCs) using a bulk heterojunction 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) and [6,6]-phenyl C71 butyric acid methyl ester (PC70BM) as active layer. The absorption spectrum and performance parameters obtained are compared to those obtained for similar iOSCs where the ETL was poly [(9,9-bis (30- (N,N-dimethylamino) propyl) -2,7-fluorene) -alt-2,7- (9,9-dioctylfluorene)] (PFN). Initially, devices showed the S-shaped current–voltage curve that has been modeled using a three-diode equivalent circuit model. This phenomenon can be removed by repeating electrical sweep-cycles under illumination. The degradation under nitrogen atmosphere and under encapsulation was also analyzed and compared with the degradation of the iOSCs using PFN. It was observed that the degradation of encapsulated HIZO-iOSC was twice slower than that of PFN-iOSCs. This increase in stability can be attributed to the Hf atoms, which have a stronger thermodynamic tendency to form metal oxides, suppressing the dissociation of HIZO.

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.

Improving the Performances of Perovskite Solar Cells via Modification of Electron Transport Layer.

The commonly used electron transport material (6,6)-phenyl-C61 butyric acid methyl ester (PCBM) for perovskite solar cells (PSC) with inverted planar structures suffers from properties such as poor film-forming. In this manuscript, we demonstrate a simple method to improve the film-forming properties of PCBM by doping PCBM with poly(9,9-dioctylfluorene-co-benzothiadiazole) (F8BT) as the electron transport layer (ETL), which effectively enhances the performance of CH3NH3PbI3 based solar cells. With 5 wt % F8BT in PCBM, the short circuit current (JSC) and fill factor (FF) of PSC both significantly increased from 17.21 ± 0.15 mA·cm−2 and 71.1 ± 0.07% to 19.28 ± 0.22 mA·cm−2 and 74.7 ± 0.21%, respectively, which led to a power conversion efficiency (PCE) improvement from 12.6 ± 0.24% to 15 ± 0.26%. The morphology investigation suggested that doping with F8BT facilitated the formation of a smooth and uniform ETL, which was favorable for the separation of electron-hole pairs, and therefore, an improved performance of PSC.

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 ...