Effective Charge Generation Research Articles

Composite side chain induced ordered preaggregation in liquid state for high-performance non-halogen solvent processed organic solar cells

Eco-friendly organic solar cells (OSCs) have become a promising choice for commercialization, particularly emphasizing the importance of using non-halogenated solvents. However, non-halogenated OSCs with high-performance remain limited due to the uncontrollable preaggregation behaviors of photovoltaic materials in these solvents. Here, composite side chain engineering was shown to enhance photovoltaic performance of non-halogenated solvents processed OSCs by developing two small molecular acceptors, C10ch-F and C10ch-Cl, and to study the preaggregation behavior in toluene. Through a combination of in situ absorption analyses and molecular dynamics simulations, we demonstrated that the cyclohexyl moiety at the tail of the linear chain acted as a fixative, effectively mitigating the entanglement of the amorphous long chains and prolonging the kinetics of film formation process, resulting in reinforced molecular packing with a preferential face-on orientation. With effective charge generation, transport, and collection, C10ch-Cl-based device from Tol showed an impressive PCE of 18.4 % and 19.2 % in the binary and ternary systems. Moreover, the PCE remained at 80 % of its initial value after 790 h of continuous illumination, indicating excellent photostability. The uncovered preaggregation and realized excellent performance obtained through the composite side chain strategy may allow for further synthetic advances, potentially leading to significantly improved eco-friendly OSCs.

Highly efficient halogen-free rigid and flexible binary organic solar cells using new solid indacene additive

Flexible Organic solar cells (OSCs) have garnered widespread attention due to the increased popularity of wearable electronic devices. To enhance the efficiency and stability of the device we have prepared (2E,2′E)-3,3'-(4,4,9,9-tetrahexadecyl-4,9-dihydro-s-indaceno[1,2-b:5,6-b'] dithiophene-2,7-diyl)bis(2-cyanoacrylic acid) (IDT) based dopant by reacting the aldehyde precursor with cyanoacetic acid in the presence of piperdine. Here, we investigate the effect of IDT on the performance of OSCs by adding IDT to star active layers PM6:Y6 and PM6:BTP-eC9 to improve OSCs' performance through morphology optimization. The addition of 5 wt% IDT significantly improved the device performance, achieving a remarkable PCE of 16.08 % for PM6:Y6 devices. The charge transport and recombination dynamics analysis showed that the appropriate concentration of IDT can provide better channels for carrier transport, promoting effective charge generation and extraction in OSCs. It is observed that the addition of IDT promotes effective generation and dissociation of excitons, thus improving OSC performance. The flexible ITO-free OSC was fabricated using PM6:Y6:IDT as the active layer film, achieving a high PCE of 12.59 % with VOC, JSC, and FF of 0.83 V, 23.21 mA/cm2 and 68.63 %, respectively. Hence, the findings indicate a reliable approach which could potentially deliver rigid and flexible OSCs with excellent performance and commercial viability.

Template-free hierarchical TiO2/rGO nanocomposites for enhanced photocatalytic performance

This work utilized a simple, cost-effective, one-pot, template-free hydrothermal technique to form a hierarchical nanocomposite having TiO2 and reduced graphene oxide (rGO). The hierarchical TiO2/rGO nanocomposite demonstrates a large surface area, resulting in higher adsorption of photons and effective charge generation, separation, and migration. As a result, the synthesized nanocomposite shows effective degradation of Rhodamine-B dye. The optimal amount of rGO effectively minimizes the charge recombination, which plays a significant role in dye degradation. The morphological, photoelectrochemical, and photocatalytic characteristics were studied by scanning and transmission electron microscopy, X-ray photoelectron spectroscopy, X-ray crystallography, photoluminescence spectra, electrochemical impedance spectroscopy, and UV–Vis spectrophotometer.

Overcoming Moisture‐Induced Charge Decay in Tribo‐Materials

AbstractThe paper extensively explores moisture‐induced charge decay in tribo‐materials, addressing charge generation fundamentals and overcoming strategies. Triboelectric effect and contact electrification models are discussed, with corona charging and hydro‐charging as effective charge generation methods. Moisture‐induced adverse effects, such as swelling and charge dissipation, are outlined. Electronegativity and dangling bonds' roles in charge traps are explored, along with the impact of functionalities on materials. Various strategies, including hydrophobic surfaces, crystalline phases, and water‐reactive materials, are proposed to counter moisture effects. Tribo‐materials are currently applied in energy, sensors, environment, and healthcare, with potential in smart skin sensors and implantable devices. Overcoming challenges, including high charge density and durability, can lead to breakthroughs, expanding applications to harsh environments like underwater and high temperatures.

Photocatalytic Degradation of Eriochrome Black-T Using BaWO4/MoS2 Composite

Photocatalytic degradation of organic compounds using semiconductor oxide materials has attracted increased attention in the recent decades. Both the catalysts and light play an important role in the photocatalytic degradation process. This research work focuses on the synthesis of BaWO4/MoS2 composite using green chemical method and its use in the degradation of Eriochrome black-T dye. Synthesized BaWO4, and BaWO4/MoS2 composites were characterized by XRD, XPS, Raman, SEM, TEM, BET and UV-Vis characterizations techniques. BaWO4/MoS2 composite exhibits superior photocatalytic performance towards Eriochrome black-T degradation than BaWO4. Superior photocatalytic activity of BaWO4/MoS2 composite corresponds to enhanced light absorption, effective charge generation, separation, and minimum recombination of photogenerated charge carriers.

Organic Solar Cells with 18% Efficiency Enabled by an Alloy Acceptor: A Two-in-One Strategy.

The trade-off between the open-circuit voltage (Voc ) and short-circuit current density (Jsc ) has become the core of current organic photovoltaic research, and realizing the minimum energy offsets that can guarantee effective charge generation is strongly desired for high-performance systems. Herein, a high-performance ternary solar cell with a power conversion efficiency of over 18% using a large-bandgap polymer donor, PM6, and a small-bandgap alloy acceptor containing two structurally similar nonfullerene acceptors (Y6 and AQx-3) is reported. This system can take full advantage of solar irradiation and forms a favorable morphology. By varying the ratio of the two acceptors, delicate regulation of the energy levels of the alloy acceptor is achieved, thereby affecting the charge dynamics in the devices. The optimal ternary device exhibits more efficient hole transfer and exciton separation than the PM6:AQx-3-based system and reduced energy loss compared with the PM6:Y6-based system, contributing to better performance. Such a "two-in-one" alloy strategy, which synergizes two highly compatible acceptors, provides a promising path for boosting the photovoltaic performance of devices.

Developement of highly efficient large area organic photovoltaic module: Effects of nonfullerene acceptor

Abstract To transfer spin-coating based high performance polymer solar cells (PSCs) to large area using roll-to-roll compatible solution process, it is important to understand effect of the processing method and materials on morphology of bulk-heterojunction (BHJ) films. We developed PBDB-T based PSCs modules using PC71BM or nonfullerene acceptor ITIC with blade coating. It is found that crystallization of ITIC and its following aggregation are significantly affected by solvent drying dynamics which is induced by thermal heating whereas PC71BM shows similar BHJ morphology regardless heating temperature. We studied mechanism and effects of acceptors on BHJ film forming during the coating. ITIC-solvent interaction makes ITIC to form high crystalline structures and but, large aggregated domains during slow solvent evaporation at room temperature. Such aggregated morphology of PBDB-T:ITIC is much improved to optimal morphology for effective charge generation and transporting with a 50 °C heating process. As a result, PBDB-T:ITIC photovoltaic module (active area 58.5 cm2) prepared at 50 °C showed much enhanced efficiency of 9.03% than 5.0% of room temperature processed one. This result is among the highest performance of large active-area PSC modules and provides research guidelines for efficient transfer of spin-coating based small cell technology to roll-to-roll based large-area PSC modules.

Design of Tandem Organic Light Emitting Diode using efficient charge generation layer

In this work, highly efficient Tandem Organic Light Emitting Diode (OLED) based on planar organic charge generation layer (CGL) of C70/Pentacene is proposed. It is found that the proposed CGL generate charges as well as exhibits organic photovoltaic type behavior. In addition a very thin layer of Al/LiF and PEDOT:PSS is used as electron and hole injection layer respectively to further increase the transport of electrons and holes from CGL to emissive unit. The current efficiency and luminance of red tandem device is found to be 29 cd/A and 29010 cd/m2 at 20 mA/cm2 and 100 mA/cm2 respectively which is 1.855 times 1.856 times greater than that of single emitter device having current efficiency and luminance of 15.63 cd/A and 15630 cd/cm2 at the same current densities Generally, the turn on voltage of Tandem devices is almost double as compared to single unit device. But with the proposed CGL the turn on voltage of red tandem device is found to be 5.9 V which is less than double the turn on voltage of single unit device (3 V). Therefore, the effective charge generation and transport property of proposed CGL as well as remarkable high injection property of thin Al layer and PEDOT:PSS leads to the enhancement in the efficiency of tandem OLED.

Efficient Tandem Organic Light Emitting Diode Using Organic Photovoltaic Charge Generation Layer

Highly efficient tandem red OLED is proposed using planar organic heterojunction based charge generation layer (CGL) of C70 (Fullerene)/CoPc (Cobalt Phthalocyanine). The proposed charge generation layer generates charges and exhibits organic photovoltaic type (OPV) behavior in the red emitter zone which helps in slower efficiency roll-off at higher current densities. In addition an ultrathin layer of Al/LiF is used as electron injection layer (EIL) so as to enhance the injection of electrons from charge generation layer to emissive unit. It is found that the tandem red device can reach current efficiency and luminance of 26 cd/A and 26039 cd/m2 at 20 mA/cm2 and 100 mA/cm2, respectively, which is 1.663 times and 1.665 times higher than the corresponding single emitter device. Moreover, it is known that the tandem device requires double turn-on voltage than conventional devices. In this work, the turn-on voltage of red tandem device (5.85 V) is found to be less than twice the voltage of conventional device (3 V). Further with the introduction of Distributed Bragg Reflector (DBR), enhancement in current efficiency and brightness of tandem red device are observed due to high reflectance property of DBR. Thus, the effective charge generation and OPV function of proposed charge generation layer as well as remarkably high injection property of EIL layer lead to the high performance tandem OLED.

Investigations on the charge transfer mechanism at donor/acceptor interfaces in the quest for descriptors of organic solar cell performance.

Herein, we theoretically and experimentally investigated the mechanisms of charge separation processes of organic thin-film solar cells. PTB7, PTB1, and PTBF2 have been chosen as donors and PC71BM has been chosen as an acceptor considering that effective charge generation depends on the difference between the material combinations. Experimental results of transient absorption spectroscopy show that the hot process is a key step for determining external quantum efficiency (EQE) in these systems. From the quantum chemistry calculations, it has been found that EQE tends to increase as the transferred charge, charge transfer distance, and variation of dipole moments between the ground and excited states of the donor/acceptor complexes increase; this indicates that these physical quantities are a good descriptor to assess the donor-acceptor charge transfer quality contributing to the solar cell performance. We propose that designing donor/acceptor interfaces with large values of charge transfer distance and variation of dipole moments of the donor/acceptor complexes is a prerequisite for developing high-efficiency polymer/PCBM solar cells.

A Double-Cable Poly(fluorene-alt-thiophene) with Bay-Substituted Perylenediimide Pendants: An Efficient Interfacial Material in Bulk-Heterojunction Solar Cells

A solution-processable double-cable polymer (PFT-PDI), composed of the backbone poly(fluorene-alt-thiophene) (PFT), the n-butoxyl linker, and the pendants perylenediimides (PDI), was developed. PFT-PDI was almost nonconductive with the hole and electron mobilities in the order of 10–10. There was no charge transfer but energy transfer from the donor PFT chain to the acceptor PDI units. With a hole-transporting channel from the stacked PFT units and an electron-transporting channel along PDI chain, PFT-PDI at the P3HT/PCBM interface facilitated the effective charge generation from P3HT excitons and charge transporting and enhanced the cell photocurrent. The encapsulated cell ITO/MoO3/P3HT:PCBM:PFT-PDI/LiF/Al with doping PFT-PDI of 3 wt % demonstrated the maximum power conversion efficiency (PCE) of 4.50%, increasing by 27.5%, relative to PCE of 3.53% from the cell without doping. The PFT-PDI doping much improved the cell’s stability with the loss of the initial PCE of 5.8%, in contrast to 29.7% from the re...

Intermixing Effect on Electronic Structures of TQ1:PC71BM Bulk Heterojunction in Organic Photovoltaics

The interface energetics and intermixing effects of the donor/acceptor bulk heterojunction (BHJ) blends of poly[2,3‐bis‐(3‐octyloxyphenyl) quinoxaline‐5, 8‐dilyl‐alt‐thiophene‐2, 5‐diyl]: [6,6]‐phenyl C71butyric acid methyl ester (TQ1:PC71BM) have been investigated using ultraviolet photoemission spectroscopy (UPS) in combination with the integer charge transfer model. The TQ1:PC71BM represents the useful model system for BHJ organic photovoltaics featuring effective charge generation and transport. It finds out that the positive integer charge state of TQ1 are equal in energy to the negative integer charge state of PC71BM, leading to a negligible potential step at TQ1:PC71BM interface and thus the vacuum level alignment. It is observed that the TQ1 accumulates on the top of TQ1:PC71BM BHJ and UPS spectra as function of various blend ratios suggest that the TQ1 mixes finely with PC71BM with the little work function modification in a wide range. In addition, no significant influence of the long‐range Coulomb interactions or the intermolecular hybridization on the occupied electronic structures is present for the well‐intermixed TQ1:PC71BM BHJs. These findings provide deep insights into the properties of BHJ blends and are beneficial for the performance optimization in organic photovoltaics.

Effect of blend composition on ternary blend organic solar cells using a low band gap polymer

This work investigates the influence of blend composition in ternary blend bulk heterojunction organic solar cells composed of poly(3-hexylthiophene-2,5-diyl) (P3HT), poly[2,1,3-benzothiadiazole-4,7-diyl[4,4-bis(2-ethylhexyl)-4H-cyclopenta [2,1-b:3,4-b′]dithiophene-siloe 2,6-diyl]] (Si-PCPDTBT) and [6,6]-phenyl C71 butyric acid methyl ester (PC71BM). The use of the low band gap Si-PCPDTBT vastly improves the spectral response, when compared to a P3HT:PC71BM binary system. The optimum blend composition occurred at a total polymer concentration of 50wt%. At low polymer concentrations, the P3HT phase was amorphous in nature. Increasing the polymer content led to the formation of crystalline polymer domains, as evidenced by XRD measurements. This significantly enhanced the charge carrier transport throughout the active layer. XPS depth profiles indicated that variations in the polymer content also influenced the mixing between the Si-PCPDTBT and the P3HT host matrix. This analysis showed that the 50wt% was conducive to a larger interaction between the two polymers. A comprehensive analysis of the relative contributions of each molecule to the photoluminescence suggested that the polymer concentration not only affects the film microstructure, it also influences the photoluminescence quantum yield of the blend. This is caused by alterations to the recombination mechanisms occurring in the constituent materials, which, in turn, influences photocurrent generation. This result shows that the overall polymer content must be chosen carefully to strike a delicate balance between improved absorption and effective charge generation and collection.

Inverted Quantum-Dot Light Emitting Diode Using Solution Processed p-Type WOx Doped PEDOT:PSS and Li Doped ZnO Charge Generation Layer.

PSS:WOx) and n-type metal oxide (lithium doped zinc oxide, LZO). The effective charge generation in solution processed p-n junction was confirmed by capacitance-voltage (C-V) and current density-electric field characteristics. It is also demonstrated that the performances of CGL based QLEDs are very similar when various substrates with different work functions are used.

Inverted Tandem Phosphorescence Organic Light-Emitting Diodes Based on <formula formulatype="inline"><tex Notation="TeX">$\hbox{MoO}_{3}/\hbox{Al/Cs}_{2}\hbox{CO}_{3}$</tex> </formula> Charge Generation Unit

A multilayer charge generation unit (CGU) $\hbox{MoO}_{3}/\hbox{Al/Cs}_{2}\hbox{CO}_{3}$ has been developed for inverted tandem organic light-emitting diodes (OLEDs). The current efficiency of inverted tandem phosphorescence OLED with $\hbox{MoO}_{3}$ (8 nm)/Al (1 nm)/ $\hbox{Cs}_{2}\hbox{CO}_{3}$ (0.5 nm) CGU is almost twice as high as that of individual electroluminescent (EL) device. Charges generate at hole-transporting host material/ $\hbox{MoO}_{3}$ interface and $\hbox{MoO}_{3}$ bulk layer, and electrons are extracted by $\hbox{Cs}_{2}\hbox{CO}_{3}$ /electon-transporting layer (ETL) interface. The significantly enhanced performance of the tandem device with $\hbox{MoO}_{3}/\hbox{Al/Cs}_{2}\hbox{CO}_{3}$ CGU compared with a $\hbox{MoO}_{3}/\hbox{Cs}_{2}\hbox{CO}_{3}$ -based one may be attributed to preventing chemical reaction of $\hbox{MoO}_{3}$ and $\hbox{Cs}_{2}\hbox{CO}_{3}$ by the inserted ultrathin Al layer. Moreover, the current efficiency and EL spectrum of another inverted tandem OLED combining red and green stack further prove the effective charge generation and separation with the multilayer $\hbox{MoO}_{3}/\hbox{Al/Cs}_{2}\hbox{CO}_{3}$ CGU. It is expected that such a CGU is a promising candidate for inverted tandem white OLED for active matrix organic light-emitting diode display driven by an n-type thin-film transistor backplane.

Effect of NaCl doped into Bphen layer on the performance of tandem organic light-emitting diodes

To improve the performance of tandem organic light-emitting diodes (OLEDs), we study the novel NaCl as n-type dopant in Bphen:NaCl layer. By analyzing their relevant energy levels and carrier transporting characteristics, we discuss the mechanisms of the effective charge generation layer (CGL) of Bphen:NaCl (6 wt%)/MoO3. In addition, we use the Bphen:NaCl (20 wt%) layer as the electron injection layer (EIL) combining the CGL to further improve the performance of tandem device. For this tandem device, the maximal current efficiency of 9.32 cd/A and the maximal power efficiency of 1.93 lm/W are obtained, which are enhanced approximately by 2.1 and 1.1 times compared with those of the single-emissive-unit device respectively. We attribute this improvement to the increase of electron injection ability by introducing of Bphen:NaCl layer. Moreover, the CGL is almost completely transparent in the visible light region, which is also important to achieve an efficient tandem OLEDs.

Balancing the white emission of OLEDs by a tandem structure with an effective charge generation layer

In this paper, we performed the design on the structure of white organic light-emitting diodes (WOLEDs). Use of a tandem structure based on lithium fluoride (LiF)-doped 4,7-diphenyl-1,10-phenanthroline (Bphen:LiF)/Al/molybdenum trioxide (MoO3) as an effective intermediate charge generation layer (CGL), which makes up for the deficiency of the color coordinates, yields relatively broadband white emission. Although single WOLEDs using 2,9-dimethyl-4,7-diphenyl-1,10-phenanthrolin (BCP) as hole blocking layer produced white light emission with Commission Internationale d’Eclairage (CIE) coordinates of (0.28, 0.39) at 10mA/cm2, the optimized tandem WOLEDs demonstrated that the color coordinates were improved to (0.41, 0.42). The maximum efficiency was enhanced from 2.73cd/A to 18.6cd/A as well.

High power efficiency tandem organic light-emitting diodes based on bulk heterojunction organic bipolar charge generation layer

The significant enhancement in power efficiency of tandem organic light-emitting diodes (OLEDs) was achieved using bulk heterojunction organic bipolar charge generation layer (CGL), consisted of zinc phthalocyanine (ZnPc): fullerene (C60) blend. In addition to a significant enhancement in luminance and current efficiency this work yielded a maximum power efficiency of 21 lm W−1 for a tandem OLED, notably almost two times higher than that of a single-unit device, with a maximum power efficiency of 10.1 lm W−1. The enhancement in power efficiency at higher luminance is also over 50%. The remarkable enhancement in power efficiency has been attributed to the effective charge generation, transport and extraction due to the presence of interface-modified ZnPc:C60 CGL in tandem OLEDs. Our results demonstrate that the bulk heterojunction, consisting of two matched n- and p-type organic semiconductors, is a promising bipolar CGL for high power efficiency tandem OLEDs.

Organic heterojunctions as a charge generation layer in tandem organic light-emitting diodes: the effect of interfacial energy level and charge carrier mobility

A homologous series of p-type thiophene organic semiconductors NaTn (naphthyl end-capped oligothiophenes, n = 2–6 represents the number of thiophene units) were employed to form organic heterojunctions with n-type organic semiconductor C60 (C60/NaTn), applied for high-performance tandem organic light-emitting diodes (OLEDs). The effect of organic heterojunctions as a charge generation layer on the performance of tandem OLEDs has been well demonstrated. We found that not only are the highest occupied molecular orbital levels of NaTn close to the lowest unoccupied molecular orbital of C60, but also that a high charge carrier mobility is very important for constructing an effective charge generation layer to achieve high power efficiency in tandem OLEDs. Our results offer a design/selection rule for organic semiconductors used to construct effective organic heterojunction charge generation layers, which will be useful in future high-performance tandem OLEDs.

A high-performance tandem white organic light-emitting diode combining highly effective white-units and their interconnection layer

By utilizing 2,9-dimethyl-4,7-diphenyl-1,10-phenanthroline:Li/MoO3 as an effective charge generation layer (CGL), we extend our recently demonstrated single-emitting-layer white organic light-emitting diode (WOLED) to realize an extremely high-efficiency tandem WOLED. This stacked device achieves maximum forward viewing current efficiency of 110.9 cd/A and external quantum efficiency of 43.3% at 1 μA/cm2 and emits stable white light with Commission Internationale de L’Eclairage coordinates of (0.34, 0.41) at 16 V. It is noted that the combination of effective single units and CGL is key prerequisite for realizing high-performance tandem WOLEDs.