Layer Of Organic Solar Cells Research Articles

Trace Solvent Additives Enhance Charge Generation in Layer‐by‐Layer Coated Organic Solar Cells

In bulk heterojunction (BHJ) organic solar cells (OSC), the photoactive layer morphology controls charge carrier generation, transport, and extraction. Obtaining the “optimum” morphology is often achieved by empiric optimization of processing conditions and post‐processing treatment. Better control over the morphology can be achieved by sequential photoactive layer‐by‐layer (LbL) deposition techniques, creating a pseudo‐bilayer OSC. Solvent additives can be used to modify the vertical component distribution, thereby enhancing OSC efficiency. However, the impact of solvent additives on device photophysics is often unclear. Here, the photophysics of LbL‐coated PM6/Y6 organic solar cells are reported. Enhanced power conversion efficiencies (PCEs) are observed when using 1‐chloronaphthalene (CN) as a solvent additive. Transient absorption (TA) spectroscopy indicates that the addition of 0.5% CN facilitates both exciton dissociation and charge separation, while excessive (>1%) use of CN causes fast geminate and non‐geminate charge recombination and consequently deteriorates device performance. The results outline routes to fine‐tune the morphology of LbL‐coated photoactive layers of OSCs and provide insight into the reasons for increased PCEs.

Solution-processed CuSCN/WS2 hole transport layer for enhancing efficiency of organic solar cells

Two-dimensional (2D) transition metal dichalcogenides (TMDs) materials have been applied in organic solar cells (OSCs), which possess excellent light transmittance, good charge carrier selectivity and high mobility. Herein, high quality 2D material of tungsten disulfide (WS 2 ) nanosheets is synthesized by liquid exfoliation method, which is used to form a double-layer hole transport layer with soluble copper(I) thiocyanate (CuSCN). The introduction of WS 2 nanosheets smooth the surface of CuSCN hole transport layers (HTL) and modify the interface between CuSCN HTL and light absorber. The cells using double-layer CuSCN/WS 2 as HTL exhibit higher light photon utilization, weaker recombination loss compared to the reference cell with pristine CuSCN HTL. More importantly, it has been proved that the WS 2 nanosheets act as intermedium between light absorbers and CuSCN, which contribute to efficient hole extraction process. As a result, a champion power conversion efficiency (PCE) of 9.00% is obtained in PTB7-Th:PC 71 BM light absorber based cell using CuSCN/WS 2 as HTL, which is > 16% higher than the PCE of 7.75% achieved in reference cell with pristine CuSCN HTL. This result proves that 2D TMDs materials are promising candidates as charge selectivity for highly efficient solar cells. • Soluble CuSCN and 2D WS 2 nanosheets were first developed as hole transport layer in organic solar cells. • The power conversion efficiency of PTB7-Th:PC 71 BM based cell using CuSCN/WS 2 as HTL is > 16% higher than the reference cell . • 2D WS 2 nanosheets play as a mediator between hole transport layer and light absorber, leading to efficient charge extraction .

Application of Graphene-Related Materials in Organic Solar Cells.

Graphene-related materials (GRMs) such as graphene quantum dots (GQDs), graphene oxide (GO), reduced graphene oxide (rGO), graphene nanoribbons (GNRs), and so forth have recently emerged as photovoltaic (PV) materials due to their nanodimensional structure and outstanding properties such as high electrical and thermal conductivity, large specific surface, and unique combination of mechanical strength and flexibility. They can be a crucial part of transparent electrodes, hole/electron transport materials, and active layers in organic solar cells (OSCs). Besides their role in charge extraction and transport, GRMs act as device protectors against environmental degradation through their compact bidimensional structure and offer good durability. This review briefly presents the synthesis methods of GRMs and describes the current progress in GRM-based OSCs. PV parameters (short circuit current, open circuit voltage, power conversion efficiency, and fill factor) are summarized and comparatively discussed for the different structures. The efficiency recently surpassed 15% for an OSC incorporating polymer-modified graphene as a transparent electrode. The long-term stability of OSCs incorporating GRMs is also discussed. Finally, conclusions and the outlook for future investigation into GRM-based devices for PVs are presented.

TiO2 nanoparticles via simple surface modification as cathode interlayer for efficient organic solar cells

Cathode interlayers (CILs) play important roles in promoting high-performance organic solar cells (OSCs). Among the commonly used CILs, metal oxides, such as ZnO, TiO 2 and SnO 2 , display suitable work function and high conductivity. However, they are usually processed under high temperature and in most cases, they are adopted in the inverted OSCs. Since high-performing non-fullerene OSCs are usually fabricated with conventional configuration, it is interesting to explore the potential application of these metal oxide materials as CIL in these cells. An efficient strategy is to use metal oxide nanocrystals as CIL to deposit onto photoactive layers. However, the as-synthesized nanocrystals have the difficulty to form smooth and dense films due to the serious aggregation. In this work, we developed a method via the surface modification of TiO 2 nanoparticles by using 4-dimethylamino benzoic acid to reduce the aggregation, so that smooth TiO 2 –N film can be formed on top of the photoactive layer. Besides, TiO 2 –N displays lower work function, which is helpful for better energy levels alignment. All these factors contribute to the improved charge generation and transport, leading to the power conversion efficiencies enhanced from 13.68% to 15.90% for PM6:BTP-4Cl solar cells. • Metal oxide nanocrystals are applied as cathode interlayer deposited onto the photoactive layer in organic solar cells. • The method via the surface modification on the TiO 2 nanoparticles by using polar acid ligand is facile. • TiO 2 –N displays lower work function, leading to better energy level alignment. • The TiO2–N based interlayer results in the PCE enhancement of PM6:BTP-4Cl type OSC from 13.68% to 15.90%.

Recent Advances in Hole-Transporting Layers for Organic Solar Cells.

Global energy demand is increasing; thus, emerging renewable energy sources, such as organic solar cells (OSCs), are fundamental to mitigate the negative effects of fuel consumption. Within OSC’s advancements, the development of efficient and stable interface materials is essential to achieve high performance, long-term stability, low costs, and broader applicability. Inorganic and nanocarbon-based materials show a suitable work function, tunable optical/electronic properties, stability to the presence of moisture, and facile solution processing, while organic conducting polymers and small molecules have some advantages such as fast and low-cost production, solution process, low energy payback time, light weight, and less adverse environmental impact, making them attractive as hole transporting layers (HTLs) for OSCs. This review looked at the recent progress in metal oxides, metal sulfides, nanocarbon materials, conducting polymers, and small organic molecules as HTLs in OSCs over the past five years. The endeavors in research and technology have optimized the preparation and deposition methods of HTLs. Strategies of doping, composite/hybrid formation, and modifications have also tuned the optical/electrical properties of these materials as HTLs to obtain efficient and stable OSCs. We highlighted the impact of structure, composition, and processing conditions of inorganic and organic materials as HTLs in conventional and inverted OSCs.

High‐Performance Indoor Organic Solar Cells Based on a Double‐Cable Conjugated Polymer

Indoor photovoltaic is one of the most important applications of organic solar cells (OSCs). As different from AM1.5G sunlight with broad spectra from the visible to near‐infrared region, the spectra of indoor light are usually located in the visible region. Therefore, a special material design for the photoactive layer to meet the requirement of indoor light is required for application in indoor photovoltaics. Herein, a wide‐bandgap double‐cable conjugated polymer is intentionally selected, which has the well‐matched absorption spectra with indoor light for use in indoor OSCs. This double‐cable polymer is used as a single photoactive layer in OSCs, providing a high power conversion efficiency of 19.44% under indoor light, which is comparable with the bulk‐heterojunction solar cells using near‐infrared electron acceptors. Moreover, the double‐cable polymer‐based indoor OSCs exhibit high storage stability. These results indicate that single‐component OSCs based on double‐cable polymers have promising applications in indoor OSCs.

Tin Oxide Electron Transport Layers for Air-/Solution-Processed Conventional Organic Solar Cells

Commercialization of organic solar cells (OSC) is imminent. Interlayers between the photoactive film and the electrodes are critical for high device efficiency and stability. Here, the applicability of SnO2 nanoparticles (SnO2 NPs) as the electron transport layer (ETL) in conventional OSCs is evaluated. A commercial SnO2 NPs solution in butanol is mixed with ethanol (EtOH) as a processing co-solvent to improve film formation for spin and slot-die coating deposition procedures. When processed with 200% v/v EtOH, the SnO2 NPs film presents uniform film quality and low photoactive layer degradation. The optimized SnO2 NPs ink is coated, in air, on top of two polymer:fullerene-based systems and a nonfullerene system, to form an efficient ETL film. In every case, addition of SnO2 NPs film significantly enhances photovoltaic performance, from 3.4 and 3.7% without the ETL to 6.0 and 5.7% when coated on top of PBDB-T:PC61BM and PPDT2FBT:PC61BM, respectively, and from 3.7 to 7.1% when applied on top of the PTQ10:IDIC system. Flexible, all slot-die-coated devices, in air, are also fabricated and tested, demonstrating the versatility of the SnO2 NPs ink for efficient ETL formation on top of organic photoactive layers, processed under ambient condition, ideal for practical large-scale production of OSCs.

Versatile methods for improving the mechanical properties of fullerene and non-fullerene bulk heterojunction layers to enable stretchable organic solar cells

A cross-linker and an elastomer are used to increase the mechanical compliance of the active layer in organic solar cells based on fullerene and non-fullerene acceptors without compromising their performance.

Comparative study on thermally evaporated and solution processed cathode modifying layers in organic solar cells

Organic solar cells have been fabricated using cathode modifying layers of thermally evaporated bathophenanthroline (Bphen), ytterbium doped Bphen (Bphen:Yb), and solution processed (N,N-dimethyl-ammonium N-oxide) propyl perylene diimide (PDINO). Compared to pristine Bphen, Bphen:Yb shows higher electron mobility and thereby increases fill factor of device, demonstrating the weak n-doping of Yb in Bphen. As a result of Fermi level pinning, Bphen:Yb forms an ohmic contact with photoactive layer, underpinning efficient electron injection and extraction of device. Compared to conventional PDINO, despite lower electron mobility, Bphen:Yb enables increased optical absorption of device and smoother morphology of device, thereby improving power conversion efficiency of device. The current research points out that the integration of thermally evaporated weakly n-doped cathode modifying layer and solution processed photoactive layer is a promising method to fabricate high-efficiency and low-cost organic solar cells.

Application of reduced graphene oxide as the hole transport layer in organic solar cells synthesized from waste dry cells using the electrochemical exfoliation method

The hole transport layer (HTL) plays an important role in improving the efficiency and stability of organic solar cells (OSCs).

Synthesis and Optical Properties of Conjugated Copolymers based on Phenoxazine and Fluorene for an Activated Layer in Polymeric Solar Cell Applications

In this research, a conjugated copolymer based on phenoxazine and fluorene units was synthesized via palladium-catalyzed Suzuki–Miyaura coupling polymerization in the presence of a Pd catalyst and K2CO3 as the base. The number-average molecular weight of conjugated polymers was obtained to be approximately 2616 g/mol with a polydispersity index of 1.65. The yield of polymerization was established to be approximately 29%. The chemical structure, average molecular weights and optical properties of the conjugated polymer were characterized via proton nuclear magnetic resonance (1H NMR) and Fourier transform infrared (FT-IR) spectroscopies, gel permeation chromatography (GPC), UV−vis and fluorescence spectroscopies. The conjugated polymer showed an optical band gap of 2.09 eV. The obtained conjugated polymers displayed fluorescence properties under an excitation wavelength of 400 nm. The conjugated polymers exhibit potential as activated layers in organic solar cells, proving the analysis results.

Matching electron transport layers with a non-halogenated and low synthetic complexity polymer:fullerene blend for efficient outdoor and indoor organic photovoltaics.

The desired attributes of organic photovoltaics (OPV) as a low cost and sustainable energy harvesting technology demand the use of non-halogenated solvent processing for the photoactive layer (PAL) materials, preferably of low synthetic complexity (SC) and without compromising the power conversion efficiency (PCE). Despite their record PCEs, most donor–acceptor conjugated copolymers in combination with non-fullerene acceptors are still far from upscaling due to their high cost and SC. Here we present a non-halogenated and low SC ink formulation for the PAL of organic solar cells, comprising PTQ10 and PC61BM as donor and acceptor materials, respectively, showing a record PCE of 7.5% in blade coated devices under 1 sun, and 19.9% under indoor LED conditions. We further study the compatibility of the PAL with 5 different electron transport layers (ETLs) in inverted architecture. We identify that commercial ZnO-based formulations together with a methanol-based polyethyleneimine-Zn (PEI-Zn) chelated ETL ink are the most suitable interlayers for outdoor conditions, providing fill factors as high as 74% and excellent thickness tolerance (up to 150 nm for the ETL, and >200 nm for the PAL). In indoor environments, SnO2 shows superior performance as it does not require UV photoactivation. Semi-transparent devices manufactured entirely in air via lamination show indoor PCEs exceeding 10% while retaining more than 80% of the initial performance after 400 and 350 hours of thermal and light stress, respectively. As a result, PTQ10:PC61BM combined with either PEI-Zn or SnO2 is currently positioned as a promising system for industrialisation of low cost, multipurpose OPV modules.

Cross-Linking of Doped Organic Semiconductor Interlayers for Organic Solar Cells: Potential and Challenges

Solution-processable interlayers are important building blocks for the commercialization of organic electronic devices such as organic solar cells. Here, the potential of cross-linking to provide an insoluble, stable, and versatile charge transport layer based on soluble organic semiconductors is studied. For this purpose, a photoreactive tris-azide cross-linker is synthesized. The capability of the small molecular cross-linker is illustrated by applying it to a p-doped polymer used as a hole transport layer in organic solar cells. High cross-linking efficiency and excellent charge extraction properties of the cross-linked doped hole transport layer are demonstrated. However, at high doping levels in the interlayer, the solar cell efficiency is found to deteriorate. Based on charge extraction measurements and numerical device simulations, it is shown that this is due to diffusion of dopants into the active layer of the solar cell. Thus, in the development of future cross-linker materials, care must be taken to ensure that they immobilize not only the host but also the dopants.

Effect of rapid thermal treatment on the electrical conductivity improvement of nc-ZnO:Bi thin film and ITO substrate

Spherical nano crystalline zinc oxide doped with bismuth (nc-ZnO:Bi) spin-coated on indium tin oxide (ITO) substrates exhibited the improvement of conductivity under the rapid thermal annealing (RTA) treatment. The ZnO:Bi nanostructure was formed at 550 °C annealing temperature, which severely affect the ITO electrical quality and closely relevant with the device performance. The efficiency of relevant electronic devices has been limited by the low electrical conductivity of the transparent electrodes. RTA treatment in the ambient atmosphere condition was applied to ZnO:Bi film coated on ITO substrate to perform the good spherical nc-ZnO:Bi properties and to persist in the ITO low resistivity, concomitantly which results in significant improvement of electrical and optical properties of nc-ZnO:Bi/ITO substrate. RTA process was subjected at varying temperature conditions from 700 °C to 930 °C for 20 s. It is noticeable that the RTA can obtain ZnO:Bi nanostructure, good optical property, and high ITO conductivity existence, simultaneously. The nano-spherical ZnO:Bi around 10–20nm diameter size at the film surface morphology provides the reflectance of 6%, and the transmittance of above 90% at 930 °C RTA for 20 s. The photocurrent of nc-ZnO:Bi/ITO films provides between 10−2 to 1 A/cm2 at 0.5 V. The RTA process can improve electrical property of ITO films with uniform distribution of oxygen vacancy. Surface morphology and crystalline grain quality of the thin film were investigated after RTA treatment. In addition, optical absorbance and energy gap (Eg) of nc-ZnO:Bi/ITO substrate evaluated by Tauc plot is a crucial attribute to apply in a promising photonic device. Thus, the high electrical and optical qualities of such nc-ZnO:Bi/ITO films can be used to produce an electron transport layer for organic solar cells and transparent contact electrodes for low-cost semiconductor devices.

Sub-nanometer atomic layer deposited Al2O3 barrier layer for improving stability of nonfullerene organic solar cells

Organic solar cells (OSCs) is a promising next-generation photovoltaic technology, however, the device stability remains to be the main barrier for its future commercialization. Herein, we reported the application of a sub-nanometer Al2O3 barrier layer in nonfullerene OSCs via atomic layer deposition (ALD), for the purpose of preventing metal ion diffusion from indium tin oxide (ITO) into the polymer layer caused by the corrosion of Poly(3,4-ethylenedioxythiophene): poly (styrenesulfonate) (PEDOT:PSS). The thickness of the ALD-Al2O3 barrier layer was precisely optimized by controlling the number of ALD cycles (n) to achieve simultaneously good photoelectric properties and conformal coverage. An average power conversion efficiency (PCE) of 15.02% was demonstrated for the optimal OSCs with ALD-Al2O3 barrier layer. The above mentioned suppression of metal ion diffusion was experimentally confirmed by the cross sectional observations of transmission electron microscopy (TEM) and chemical mapping from energy-dispersive X-ray spectroscopy (EDX), resulting in a significantly improved operational stability with a device lifetime 3-times longer than that without ALD-Al2O3 barrier layer. Such ALD-assisted interface modification provides an effective approach to realize high-performance and stable OSCs.

Investigation of Dye Dopant Influence on Electrooptical and Morphology Properties of Polymeric Acceptor Matrix Dedicated for Ternary Organic Solar Cells.

The publication presents the results of investigations of the influence of dye dopant on the electrooptical and morphology properties of a polymeric donor:acceptor mixture. Ternary thin films (polymer:dye:fullerene) were investigated for potential application as an active layer in organic solar cells. The aim of the research is to determine the effect of selected dye materials (dye D131, dye D149, dye D205, dye D358) on the three-component layer and their potential usefulness as an additional donor in ternary cells, based on P3HT donor and PC71BM acceptor. UV–vis spectroscopy studies were performed, and absorption and luminescence spectra were determined. Ellipsometry parameters for single dye and ternary layers have been measured. The analyses were performed using the Raman spectroscopy method, and the Raman spectra of the mixtures and single components have been determined. Organic layers were prepared and studied using scanning electron microscope and atomic force microscope. For dyes, ultraviolet photoelectron spectroscopy and X-ray photoelectron spectroscopy studies were carried out and the ternary system was presented and analyzed in terms of energy bands.

Modulation of Vertical Component Distribution for Large‐Area Thick‐Film Organic Solar Cells

Thick active layers in organic solar cells (OSCs) have a great promise of enhancing light absorption and providing pinhole‐free films for large‐scale fabrication. Since charge carriers in thick films need a longer transporting path in the vertical direction to the electrode than in thin films, modulation of the active layer morphology in thick films is highly required for effective charge transport. Herein, thin‐film (≈110 nm) and thick‐film (≈300 nm) OSCs based on a PM6:IT‐4 F film are fabricated by blade coating with various additive contents. It is found that the optimized thick‐film device needs more additives than the optimized thin‐film device. The addition of more additives in thick‐films promotes vertical component distribution and enhances the crystallization, resulting in efficient charge transport with reduced charge recombination and electron (or hole) accumulation within the thick active layer. These results are also confirmed by PM6:Y6‐based devices, in which optimized thin‐film and thick‐film devices exhibit power conversion efficiency (PCE) of 16.69% and 14.91% at the additive contents of 0.3% and 0.6%, respectively. Encouragingly, thick‐film device with 0.6% additive has a narrow distribution of PCE values, and high PCEs of 13.94% and 13.05% are obtained for the large‐area (1 cm2) rigid and flexible thick‐film OSCs, showing great application prospect.

Fluidic Manipulating of Printable Zinc Oxide for Flexible Organic Solar Cells.

As a representative electron transporting layer in organic solar cells, zinc oxide (ZnO) can be fabricated by the meniscus-guided coating with the promotion of sol-gel technology. In order to fabricate stable and flexible organic solar cells (OSCs) based on the printable ZnO layers, here, a new method for simultaneously manipulating fluidics of the sol-gel ZnO precursor and optimizing processability of the ZnO layer for flexible OSCs is developed. It is found that the Marangoni recirculation in meniscus and the annealing temperature of the sol-gel ZnO precursor can be effectively modulated by changing the Lewis base. With the use of propylamine, the high-quality ZnO layer that is suitable for flexible OSCs can be fabricated through blade coating. Under such a condition, the formation of polar facet in ZnO layer is well restrained, which favors the photostability of the cells. As a result, the best 1.00 cm2 flexible cell outputs a power conversion efficiency of 16.71%, which is the best value till now.

Solution-Processed Copper Oxide Thin Film as Efficient Hole Transport Layer for Organic Solar Cells

Solution-Processed Copper Oxide Thin Film as Efficient Hole Transport Layer for Organic Solar Cells

Uncovering the out-of-plane nanomorphology of organic photovoltaic bulk heterojunction by GTSAXS

The bulk morphology of the active layer of organic solar cells (OSCs) is known to be crucial to the device performance. The thin film device structure breaks the symmetry into the in-plane direction and out-of-plane direction with respect to the substrate, leading to an intrinsic anisotropy in the bulk morphology. However, the characterization of out-of-plane nanomorphology within the active layer remains a grand challenge. Here, we utilized an X-ray scattering technique, Grazing-incident Transmission Small-angle X-ray Scattering (GTSAXS), to uncover this new morphology dimension. This technique was implemented on the model systems based on fullerene derivative (P3HT:PC71BM) and non-fullerene systems (PBDBT:ITIC, PM6:Y6), which demonstrated the successful extraction of the quantitative out-of-plane acceptor domain size of OSC systems. The detected in-plane and out-of-plane domain sizes show strong correlations with the device performance, particularly in terms of exciton dissociation and charge transfer. With the help of GTSAXS, one could obtain a more fundamental perception about the three-dimensional nanomorphology and new angles for morphology control strategies towards highly efficient photovoltaic devices.