Active Layer Solution Research Articles

A Study on Improving the Sensitivity of Indirect X-ray Detectors by Adding Hybrid Perovskite Quantum Dots

In this paper, we demonstrate the enhancement in detection sensitivity of an indirect X-ray detector based on poly(3-hexylthiophene) (P3HT) and fullerene derivatives [6,6]-phenyl-C71-butyric acid methyl ester (PC71BM) by adding perovskite quantum dots (PeQDs). The weight ratio of P3HT and PC71BM was fixed at 1:1 (20 mg/mL in chlorobenzene), and different amounts of FAPbBr3 PeQDs of (0–3) mg were added to the P3HT:PC71BM active layer solution. The experimental results show that the detector using P3HT:PC71BM:FAPbBr3 PeQDs (1 mg) achieved a sensitivity of 2.10 mA/Gy∙cm2. To further improve the sensitivity, a ligand exchange experiment was performed on the P3HT:PC71BM:FAPbBr3 PeQDs (1 mg) detector. Under the condition of 12 h ligand exchange time, the detector with P3HT:PC71BM:FAPbBr3 PeQDs (1 mg) showed the highest sensitivity of 2.26 mA/Gy∙cm2, which was increased by 28% compared to the pristine detector with a P3HT:PC71BM active layer.

Flexible Blade‐Coated Optoelectronic Devices: Dual Functionality via Simultaneous Deposition

AbstractAdvances in printing techniques have enabled a new generation of low‐cost and large‐area flexible electronics. However, in applications where a combination of printed components is required, multiple fabrication processes and subsequent integration can be complex and time consuming. Additionally, these applications require devices to be stacked atop each other, reducing overall mechanical flexibility. In this work, surface‐energy‐patterning (SEP) is used to enable simultaneous blade coating of organic photodiode (OPD) and organic light‐emitting diode (OLED) films side‐by‐side. The result is dual functionality on a single flexible substrate. Various active layer solution concentrations are investigated to optimize active layer thicknesses and consequently optimize the performance of each device. A peak spectral responsivity of 0.33 A W−1 at 800 nm is achieved for optimized OPDs and a maximum luminance of 7000 cd m−2 is achieved for optimized OLEDs at an applied bias of 8 V. Overall, this technique enables the printing of two functionally distinct devices in a single step without compromising the performance of either device.

Improvement of Indirect X-ray Detector Performance by Applying Additive Solvent to the Organic Active-Layer.

In this paper, we studied how the sensitivity of an indirect X-ray detector was changed by adding the additive solvent DIO to the organic active-layers, such as P3HT:PCBM and PBDB-T:PCBM. The crystallinity and absorbance of the active-layer films were compared with different additive DIO contents. In both active-layers, the highest crystallinity and absorbance were obtained when 3 v% of the DIO was mixed with the active-layer solution. At the same mixing condition of the DIO, the highest sensitivity, of 1.17 mA/Gy · cm₂, was obtained for the P3HT:PCBM detector, and the highest sensitivity, 1.87 mA/Gy · cm₂, was obtained for the PBDB-T:PCBM detector. Compared to the detector without the DIO, the sensitivities of the detectors with the P3HT:PCBM and PBDB-T:PCBM increased by 18.12% and 20.27%, respectively.

Fabrication of high-performance solution processed thin film transistors by introducing a buffer layer

In this paper, high quality ZrO2 and In2O3 films were prepared by solution method. Based on the solution-processed ZrO2 dielectric and In2O3 semiconductor layer, bottom-gate top-contact thin-film transistors (TFTs) were integrated. XPS depth profile was carried out to investigate the intersecting region between ZrO2 insulator and In2O3 active layer due to the diffusion of the subsequent precursor solution, and the effect of intersecting region on the electrical performance of TFTs was discussed. In order to narrow the intersecting region, a simple way that introducing a buffer layer between the active layer and the insulating layer was proposed. The effect of buffer layer was investigated by the multifactor analysis on Minitab software and the result indicated that the buffer layer can effectively improve the performance of TFTs. Finally, high-performance solution processed Thin Film Transistor was fabricated with 0.05 M buffer layer solution and 0.10 M active layer solution. Compared with the TFT without buffer layer, the mobility of TFT with buffer layer increased from 4.35 to 43.94 cm2/Vs, and the Ion/Ioff increased from 1.87 × 105 to 3.90 × 106.

Revealing working mechanisms of PFN as a cathode interlayer in conventional and inverted polymer solar cells.

Energy level alignments at the PC71BM/PFN/Ag interface in conventional polymer solar cells (c-PSCs) and the ITO/PFN/PC71BM interface in inverted polymer solar cells (i-PSCs) are systematically investigated via ultraviolet photoelectron spectroscopy and by using the integer charge transfer (ICT) model. The findings demonstrate that PFN as a cathode interlayer is able to effectively reduce the electron extraction barriers from 0.72 eV to 0.38 eV for the c-PSCs and from 0.58 eV to 0.36 eV for the i-PSCs, respectively. In the c-PSCs, the final modified electron extraction barrier matches the predicted value (∼0.4 eV) using the ICT model. In the i-PSCs, there exists an intermixing layer of PFN and the active layer above PFN because some PFN is dissolved by the organic solvent in the active layer solution, resulting in a special energy level alignment at the PFN/PC71BM interface. ITO/PFN (2 nm)/PC71BM (20 nm) in the i-PSCs actually forms such an interface as ITO/PFN/PFN:PC71BM with an energy level alignment like Al/LiF/PC71BM/PFN (0.65 nm), which rationalizes a higher short circuit and fill factor in the i-PSCs than c-PSCs. Finally, a general model to simulate the intermixing layer between the organic cathode interlayer and the active layer has been proposed to describe the energy level alignment of the complicated interfaces in the i-PSCs.

Influence of Interface Doping on Charge-Carrier Mobilities and Sub-Bandgap Absorption in Organic Solar Cells

P3HT:PCBM (poly(3-hexylthiophene-2,5-diyl):([6,6]-phenyl-C61-butyric acid methyl ester)-based bulk heterojunctions (BHJs) were doped by using 4-toluenesulfonic acid (TSA) as dopant. This approach was inspired by the well-known interfacial doping of the active layer via the electron-blocking layer PEDOT:PSS (poly(3,4-ethylenedioxy-thiophene):poly(styrenesulfonate)) at its interface. TSA is amphiphilic, acidic, and structurally very similar to the monomeric building block of PSS. Upon TSA doping, a notable increase in the light absorption in the sub-bandgap region of pristine P3HT was observed. These features are assigned to polaron transitions within P3HT; however, the TSA impact on polaron absorption features in the BHJ is rather small. Although, for small TSA concentrations and thick active layers (∼220 nm) the fill factor of the solar cells improved dramatically with increasing TSA content in the active layer, which is discussed in terms of contact resistances at interfaces in the present paper. For 0.5% TSA concentration in the active layer solution the maximum of the power conversion efficiency was obtained. At the same time, the reproducibility of solar cell performance parameters was considerably improved.

프탈이미드 유도체를 기본으로 하는 공액고분자의 합성과 특성, 그리고 태양전지의 적용

프탈이미드 유도체와 티오펜 단량체들을 이용하여 새로운 고분자인 poly((5,5-(2-butyl-5,6-bisdecyloxy-4,7-dithiophen-2-yl-isoindole-1,3-dione))-alt-(2,5-thiophene))(T-TI24T)를 Stille법을 이용하여 합성하였다. T-TI24T의 수평균 분자량은 86500 g/mol로 매우 높으며 클로로포름, 1,2-디클로로벤젠, 톨루엔과 같은 용매에 매우 잘 용해된다. 또한 <TEX>$380^{\circ}C$</TEX>까지 매우 우수한 열적 안정성을 갖고 있다. T-TI24T는 꽤 낮은 호모에너지 준위(-5.33 eV)를 갖고 있다. 서로 다른 T-TI24T와 (6)-1-(3-(methoxycarbonyl)-{5}-1-phenyl[5,6]-fullerene(PCBM)의 무게비를 갖는 블렌드를 광활성층으로 하는 태양전지를 제작하여 특성을 살펴본 결과 고분자와 PCBM의 비율이 1:3일 때 가장 최적화된 결과를 보였으며, 이 때 광전변환 효율과 개방전압은 각각 0.199%와 0.99였다. T-TI24T 기반 태양전지들은 비록 매우 작은 광전변환 효율을 갖지만 잘 알려진 P3HT:PC61BM으로 구성된 태양전지와 비교해 큰 매우 큰 개방전압을 갖는다(약 0.5 V). A new copolymer named T-TI24T (poly((5,5-(2-butyl-5,6-bisdecyloxy-4,7-di-thiophen-2-yl-isoindole-1,3-dione))- alt-(2,5-thiophene))) based on phthalimide derivative and thiophene is synthesized by the Stille-coupling reaction. The polymer shows relatively high number average molecular weight of 86500 g/mol with good solubility in common organic solvents such as chloroform, 1,2-dichlorobenzene, and toluene and is thermally stable up to <TEX>$380^{\circ}C$</TEX>. Besides, it possesses a relatively low highest occupied molecular orbital (HOMO) energy level of -5.33 eV, promising the high open circuit voltage (<TEX>$V_{oc}$</TEX>) for photovoltaic applications. Active layer solution of polymer T-TI24T-as a donor and (6)-1-(3-(methoxycarbonyl)- {5}-1-phenyl[5,6]-fullerene (PCBM)-as an acceptor in different weight ratios is applied to fabricate the polymer solar cell devices. The ratio of polymer/PCBM affects the solar cell efficiency and the best performance exhibits in the device with polymer/PCBM = 1:3 (w/w), which shows a power conversion efficiency (PCE) of 0.199% and a <TEX>$V_{oc}$</TEX> of 0.99 V, respectively. Even though the device shows the very low PCE, the <TEX>$V_{oc}$</TEX> is higher than that of well known bulk heterojunction type solar cell based on P3HT:PC61BM (c.a. 0.5 V).

Self-Organized Hole Transport Layers Based on Polythiophene Diblock Copolymers for Inverted Organic Solar Cells with High Efficiency

Novel fluoroalkyl side-chain diblock copolymers, poly(3-hexylthiophene)-block-poly[3-(4-(3,3,4,4,5,5,6,6,7,7,8,8,8-tridecafluorooctyloxy)phenyl)decyloxy)thiophene] (P3HT-b-P3FAT), were successfully synthesized by Grignard metathesis (GRIM) polymerization. Driven by the low surface energy of fluoroalkyl side chains, the fluorinated polymers can spontaneously segregate on the surface of poly-(3-hexylthiophene) (P3HT) during spin-coating processes. As the P3HT block increases in the copolymer, higher concentrations of fluoropolymers are required to form the self-assembled monolayer on the surface. The fluorinated part forms an interfacial dipole that shifts the work function of the anode metal, while the P3HT block can interact with the P3HT donor for hole transport. With this self-assembly hole transport layer to align the energy levels, P3HT:PCBM photovoltaic devices are easily fabricated to achieve improved performance. Overall, devices prepared with 1.5 mg mL–1 copolymer PFT-3HT with a 3:1 ratio of P3HT to P3FAT block in the active layer solution displayed PCE values of up to 4.6% (50% PCE increase over a PEDOT:PSS control device) and showed a significant long-term stability in excess of 300 h in air.

TiO2 nanowire electron transport pathways inside organic photovoltaics

Charge transport is one of the five main steps in the operation of organic photovoltaics, but achieving balanced hole and electron transport with high mobility has been challenging in devices. Here, we report improved charge transport in organic photovoltaics via incorporation of nanostructured inorganic electron transport materials into the active layers of devices. Co-depositing TiO2 nanowires with the organic active layer solution embeds the nanowires directly within active layers of the solar cell. The ability of these nanowires to transport electrons is compared with neat P3HT:PCBM active layers and also devices containing TiO2 nanotube aggregates. Incorporation of TiO2 nanowires yields a six-fold increase in the electron mobility relative to unmodified devices, leading to a 19% improvement in the power conversion efficiency. Lower energetic disorder of the film and more balanced charge transport are also observed upon incorporating TiO2 nanowires. These advantageous effects correlate with the TiO2 nanowire length.

Morphological and topographical characterizations in spray coated organic solar cells using an additional solvent spray deposition

In a spray coating process, characteristic performance of organic solar cells (OSCs) is limited by some drawbacks such as isolated droplets, non-uniform surface and pinholes. We have investigated the film formation, surface topography and the morphology of spray coated active layers with additional solvent implemented by using an additional solvent spray deposition. Highly efficient OSCs with improved interconnection among droplets and reduced amount of pinholes were obtained by additionally spraying o-dichlorobenzene as a solvent after the conventional spray coating of the mixed solution of poly(3-hexylthiophene):[6,6]-phenyl-C 61-butyric acid methyl ester in chlorobenzene to form active layer solution. Moreover, the additional solvent spray causes changes in the matrix of the active layer resulting in the effective thermal annealing in terms of the power conversion efficiency of the OSCs.

Simple roll coater with variable coating and temperature control for printed polymer solar cells

A simple and low cost thin film solution processing system comprising a single roll coating machine has been developed to allow direct investigation of variable parameter effects in roll-to-roll processing. We present roll coating of the active layers in polymer solar cells and validate the instrument by reinvestigating the well known effect of solvent on performance. We obtained a maximum power conversion efficiency of 1.6% for the reference cells, which compares well with reported roll-to-roll coated cells according to ProcessOne, with a relative deviation caused by solvent type nearing 40% on roll coated cells, confirming the solvent to have a significant influence on the performance of the finished cell. We further present a slot-die coating head with an ultra low dead volume allowing for the preparation of roll coated polymer solar cells on flexible substrates with nearly no loss of solution, enabling roll coating testing of new polymers where only small amounts are often available. We demonstrate the formation of >50 solar cells (each with an active area of 1 cm 2) with printed metal back electrodes using as little as 0.1 mL of active layer solution. This approach outperforms spin coating with respect to temperature control, ink usage, speed and is directly compatible with industrial processing and upscaling.

Controlling Vertical Morphology within the Active Layer of Organic Photovoltaics Using Poly(3-hexylthiophene) Nanowires and Phenyl-C61-butyric Acid Methyl Ester

In this study, we demonstrate how the vertical morphology of bulk heterojunction solar cells, with an active layer consisting of self-assembled poly(3-hexylthiophene) (P3HT) nanowires and phenyl-C(61)-butyric acid methyl ester (PCBM), can be beneficially influenced. Most device fabrication routes using similar materials employ an annealing step to influence active layer morphology, but this process can create an unfavorable phase migration where P3HT is driven toward the top of the active layer. In contrast, we demonstrate devices that exhibit an increase in relative fullerene concentration at the top of the active layer by introducing the donor phase as a solid nanowire in the active layer solution and altering the pre-spin drying time. X-ray photoelectron spectroscopy and conductive and photoconductive atomic force microscopy provide detailed images of how the surface of the active layer can be influenced; this is done by tracking the concentration and alignment of P3HT and PCBM domains. Using this new procedure, devices are made with power conversion efficiencies surpassing 2%. Additionally, we show that nanowires grown in the presence of the fullerene perform differently than those that are grown and mixed separately; exposure to the nanowire during self-assembly may allow the fullerene to coat nanowire surfaces and influence the photocurrent within the device.

Studies on polyethylene glycol/polyethersulfone composite membranes for FCC gasoline desulphurization by pervaporation

A polyethylene glycol (PEG)/polyethersulfone (PES) composite membrane that can be applied on a commercial (or scale up) plant for fluid catalytic cracking (FCC) gasoline desulphurization was prepared through pre-wetting combined with double-layer coating methodology. Preparation methodology, morphologies characterization and performance test for the composite membranes were conducted. The results indicated that the pre-wetting method effectively confined the intrusion of PEG solution to porous PES support layer in coating process. The composite membrane had a clear-cut boundary surface between the dense active layer and the porous support layer, which was examined by scanning electron microscope (SEM). Pervaporation (PV) experiments indicated that the membrane, with the crosslinking agent amount of 17% and solids content in active layer solution of 16%, had a stable performance for FCC desulphurization. The sulphur enrichment factor came to 3.63, and the total permeation flux was 3.37 kg/m 2 h. It was found that the PV performance of the composite membrane changed slightly when the thickness of active layer varied from 4.25 μm to 33.26 μm.