Electrode For Organic Solar Cells Research Articles

Influence of deposition temperature and hydrogen on sustainable and transfer-free graphene transparent electrode for organic solar cells

The transfer-free graphene transparent conducting electrode (TCE) is a promising alternative to indium tin oxide (ITO) for organic solar cells (OSCs). In the present work, a comprehensive investigation on how deposition temperature and H2 flow rates affect the growth, structural, optical, and electrical properties of graphene produced by RF plasma enhanced chemical vapor deposition using sustainable sources was conducted. Inverted-geometry OSCs with P3HT: PCBM photoactive layer were fabricated on transfer-free graphene TCEs developed under different conditions. Moreover, the coupling of silver nanowires (AgNWs) with different graphene films was studied for hybrid graphene-AgNWs TCEs for OSCs. Devices based on graphene TCEs prepared at low or zero H2 flow have shown better performances than those at high flow of H2. Similarly, graphene TCEs prepared at high temperature (>700 °C, on quartz) led to a deteriorated device performance due to the highly increased growth of vertically oriented graphene nanosheets, which dramatically reduced film transmittance and increased surface roughness. The present work provides solid understanding of the growth mechanism of RF-PECVD graphene on glass from a sustainable carbon source. More importantly, the sustainable, ecofriendly, cost- and time-effective production of scalable transfer-free graphene TCEs for OSCs is optimized which paves the way towards ITO-free optoelectronics.

Facile fabrication of conductive graphitic carbon films as transparent electrodes in organic solar cells by ion beam irradiation of polystyrene films and carbonization

Conductive graphitic carbon films were fabricated from insulating polystyrene (PS) by ion beam irradiation and subsequent thermal treatment, and used as a transparent anode for organic solar cells (OSCs). Analyses of optical and chemical properties revealed that the thermally resistant oxidized carbon clusters in the PS precursors (spin-coated on quartz) were efficiently generated by ion beam irradiation at a fluence of 2 x 1016 ions/cm2, and transformed to graphitic carbon thin films through high-temperature treatment. The graphitic carbon films exhibited thickness-dependent conductivity (the highest conductivity of 374 S/cm), while their work function (5.20 eV) and surface roughness (0.560–0.596 nm) were unaffected by the thickness of the films. Furthermore, the introduction of the 10.2 nm-thick graphitic carbon films into poly(3-hexylthiophene) (P3HT): [6,6]-phenyl-C61 butyric acid methyl ester (PCBM)-based OSCs resulted in a power conversion efficiency (PCE) of 1.40%, demonstrating the feasibility of using the graphitic carbon films as transparent electrodes.

Stability enhancement of silver nanowire-based flexible transparent electrodes for organic solar cells

Flexible organic solar cells (OSCs) are one of the most promising power sources for wearable electronics. A high-quality transparent electrode is one of the indispensable components for OSCs because it guarantees sufficient light transparency and electrical conductivity. Silver nanowires (AgNWs) are considered to be an ideal candidate over commercial rigid indium tin oxide as flexible transparent electrodes (FTEs) because of their superior optoelectronic properties, excellent mechanical flexibility, solution treatability, and high compatibility with semiconductors. However, the stability of AgNWs-based FTEs (AgNWs-FTEs) hinders their further application. In this perspective, we provide state-of-the-art solution-processed AgNWs with enhanced stability and their applications in flexible OSCs. We start with a systematic analysis of the failure mechanisms and evaluation methods of AgNWs-FTEs. Then the key reinforced materials are summarized. Next, the main stability enhancement strategies are briefly discussed. Applications of AgNWs-FTEs in flexible and stretchable OSCs are further surveyed. Finally, an outlook on the current status, future challenges, and emerging strategies in this field is presented.

Amine-Free ZnO Precursor to Suppress Dedoping of PEDOT Electrodes for All-Solution-Processed Flexible Organic Solar Cells

Poly(3,4-ethylenedioxythiophene):poly(styrenesulfonate) (PEDOT:PSS) is a widely used solution-processed electrode in organic solar cells with the advantages of high electrical conductivity and high optical transparency. Highly oxidized (doped) states are the origin of its high electrical conductivity. However, PEDOT can be readily dedoped by reductive reagents, such as amines. Traditional sol–gel ZnO precursors (including ethanolamine and zinc acetate in 2-methoxyethanol denoted as ZnOEA) cause dedoping when deposited on top of PEDOT to produce low work function for electron collection. In this work, we report that an amine-free precursor of ZnO (zinc acetate dehydrate in methanol denoted as (ZnO)EA-free) is introduced to replace traditional ZnO precursors, which can suppress the chemical dedoping of PEDOT:PSS films. PEDOT:PSS remains higher optical transmittance and electrical conductivity after coating (ZnO)EA-free than ZnOEA films. All-solution-processed flexible devices with the device structure of PET/PEDOT:PSS/(ZnO)EA-free/PEI/PM6:L8-BO/PEDOT:F/PEDOT:PSS show a power conversion efficiency of 11.9% with an open-circuit voltage of 0.87 V, a short-circuit current of 20.8 mA cm–2, and a fill factor of 0.66.

Carbon-Based Electrodes for Organic Solar Cells.

Organic solar cells (OSCs) are a promising low-cost thin-film photovoltaic technology while the fabrication of transparent conductive oxide (TCO) and metal electrodes still remains a factor that hinders the scaling-up and commercialization of OSCs. Carbon-based materials are regarded as potential alternatives due to their excellent properties, such as low cost, solution processibility, high conductance, and good chemical stability. In this mini-review, the recent progress of carbon-based materials such as graphite, carbon nanosheets, graphene, and carbon nanotubes to replace the TCO and metal electrodes of OSCs is surveyed. The preparation methods of different carbon-based materials are also discussed. Based on current progress, we summarize the outlooks and challenges of carbon-based electrodes. We anticipate this mini-review will inspire more research efforts to develop high-performance and OSC-matched carbon materials for more efficient and stable carbon-electrode-based OSCs.

Printing of Low‐Melting‐Point Alloy as Top Electrode for Organic Solar Cells

AbstractThe top electrodes of organic solar cells (OSCs) are usually deposited by thermal evaporation in vacuum, which has become the major obstacle toward fully‐printed OSCs. The vacuum‐free printed top electrodes are highly desirable for the continuous production of OSCs. Here, the printing of low‐melting‐point alloy (LMPA) as cathodes in OSCs based on the D18:Y6 system is investigated. The Field's metal (FM) is focused with a melting point of 62 °C, which could be printed under moderate temperatures that are harmless to the active layers and solidifies at room temperature. More importantly, FM will not melt by solar radiation under practical scenarios. Direct ink writing is used to print the FM cathodes. Two printing modes are identified: the dragging mode in the far field to obtain rod electrodes, and the shearing mode in the near field to achieve relatively flat lamellas. The correlations between processing parameters and properties of the printed electrodes are elucidated. OSCs with printed FM cathodes exhibit the highest power conversion efficiency of 16.44%. The results demonstrate that this facile and robust direct LMPA writing technique is promising for high‐performance fully‐printed OSCs.

Performance optimization of non-fullerene acceptor organic solar cell by incorporating carbon nanotubes as flexible transparent electrode

The Power Conversion Efficiency (PCE) of an Organic Solar Cell (OSC) is largely determined by the Transparent Conductive Electrode (TCE). ITO, the most commonly used TCE, degrades the device performance on flexible plastic substrate due to its brittleness and formation of cracks under mechanical stress. As a result, an alternative TCE is required to optimize OSC output. Owing to their high optical transparency, low sheet resistance, and high mobility, carbon nanotubes have gotten a huge interest as an electrode in organic solar cells. The present work uses the software SCAPS 1-D to simulate the performance of the NFA-BHJ-OSC with a transparent electrode of Carbon nanotubes doped with Molybdenum trioxide (MoO3). The optimized PCE of 22.71 %, Fill Factor (FF) of 63.14 %, Jsc of 38.38 mA/cm2 and Voc of 0.9371 V are shown in the current simulation-based work by varying the band gap of MoO3 doped CNTs. Also, upgrading the simulated cell's hole transport Layer with CuI, Cu2O, and CuSCN HTLs yields an optimizedresult with CuSCN HTL, having PCE of 27.57 %, FF of 70.88 %, Jsc of 37.12 mA/cm2, and Voc of 1.0477 V. These results show that BHJ-OSCs using CNT as a TCE hold promise to elevate the device performance of OSC in the near future.

Silver Thin‐Film Electrodes Grown by Low‐Temperature Plasma‐Enhanced Spatial Atomic Layer Deposition at Atmospheric Pressure

AbstractThe unique properties of atomic layer deposition (ALD) are mainly exploited for metal oxides, while the growth of metals, such as silver, is still in its infancy. Low growth temperatures and high growth rates are essential to achieve conductive (i.e. percolated) films. Here, a study based on the authors’ recently introduced N‐heterocyclic carbene‐based Ag amide precursor [(NHC)Ag(hmds)] (1,3‐di‐tert‐butyl‐imidazolin‐2‐ylidene silver(I) 1,1,1‐trimethyl‐N‐(trimethylsilyl) silanaminide) using plasma‐enhanced spatial ALD at atmospheric pressure and at deposition temperatures as low as 60 °C, is provided. The favorable reactivity and high volatility of the [(NHC)Ag(hmds)] precursor affords high growth rates up to 3.4 × 1014 Ag atoms cm–2 per cycle, which are ≈2.5 times higher than that found with the established triethylphosphine(6,6,7,7,8,8,8‐heptafluoro‐2,2‐dimethyl‐3,5‐octanedionate) silver(I) [Ag(fod)(PEt3)] precursor. Consequently, highly conductive Ag films with resistivities as low as 2.7 µΩ cm are achieved at a deposition temperature of 100 °C with a percolation threshold of ≈2.6 × 1017 Ag atoms cm–2, which is more than 1.6 times lower compared to [Ag(fod)(PEt3)]. As a concept study, conductive Ag layers are used as bottom electrodes in organic solar cells, that achieve the same performance as those based on Ag electrodes resulting from a high vacuum process.

유기박막 태양전지용 ITO 투명전극 최적화 연구

This study analyzes the optical characteristics of the ITO thin film deposited using DC magnetron sputtering to study the characteristics of ITO transparent electrodes for organic solar cells deposited by sputtering. For the experiments, the pressure ranged from 1–3 mTorr, and the applied voltage ranged from 260–340 V at 10 V intervals.
 The results of light transmittance, refractive index, and surface images were analyzed using equipment such as a spectrophotometer, an elliptical polarization analyzer, and a scanning microscope. As a result, under a pressure of at least 1 mTorr, light transmittance of at least 90% was measured, and the refractive index of the thin film had an excellent value of at least 2. Therefore, optimal conditions were established for the application of ITO transparent electrodes for organic solar cells.

(Invited) Toward Nanocarbon Materials-Based Organic and Perovskite Solar Cells

In this presentation, we introduce our recent research progress on organic and perovskite solar cells using functionalized nanocarbon materials. We applied wet-processed scalable single-walled carbon nanotubes (SWCNT) films to transparent and back electrodes in organic solar cells for large area solar cells. Gas-phase growth SWCNT was dispersed with sodium dodecylbenzenesulfonate surfactant in an organic solvent and solution-coated on a treated glass substrate to make a SWCNT film as a transparent electrode. We achieved the first high efficiency e-DIPS/wet-processed SWCNT film electrode in organic solar cells with a best-efficiency of 5.93% through the optimized HNO3 doping methodology.We also report enhanced hole-transporting ability of widely utilized poly(3,4-ethylenedioxythiophene)-poly(styrenesulfonate) (PEDOT:PSS) achieved by applying cationic nitrogen-doped graphene (CNG) as a p-type modifier for efficient organic solar cells. The power conversion efficiency of the CNG-coated PEDOT:PSS-applied OSC reaches 2.76% using poly(3-hexylthiophene), which is an increase of 40% compared to that of the pristine PEDOT:PSS-applied OSC (1.96%). This technology improved the efficiency of organic solar cells using a low-bandgap polymer from 6.54% to 7.79%. The significantly enhanced performance is contributed by the increased hole-transporting ability, and the improved interfacial morphology of PEDOT:PSS.

“Reinforced concrete”-like flexible transparent electrode for organic solar cells with high efficiency and mechanical robustness

“Reinforced concrete”-like flexible transparent electrode for organic solar cells with high efficiency and mechanical robustness

Scalable eDIPS-based single-walled carbon nanotube films for conductive transparent electrodes in organic solar cells

This letter demonstrates the scalable enhanced direct-injection pyrolytic synthesis (eDIPS)-based, wet-processed single-walled carbon nanotube (SWCNT) films for high-performance organic solar cells (OSCs) using acid dopants. Thanks to the good conductivity and smooth interfacial morphology of the 60 wt% HNO3-doped eDIPS-based SWCNT film, a power conversion efficiency (PCE) of 1.78% was achieved in a P3HT:PCBM OSC. In addition, the 60 wt% HNO3-doped eDIPS-based SWCNT film indicated excellent compatibility with a record-high PCE of 4.93% was achieved in a PBTZT-stat-BDTT-8:PCBM OSC.

Highly transparent and conductive MoO3/Ag/MoO3 multilayer films via air annealing of the MoO3 layer for ITO-free organic solar cells

Air annealing of MoO3 bottom layer is a simple and highly efficient surface treatment method to prepare ultrathin, continuous, and smooth Ag layers in MoO3/Ag/MoO3 (MAM) transparent conductive films (TCFs) for indium tin oxide (ITO)-free organic solar cells (OSCs). Air annealing can readily oxidize MoO3 surface and increase surface energy of the MoO3 layer, which significantly enhances the adhesion between Ag and MoO3. When the MoO3 bottom layer is annealed at 200 °C, moreover, the treatment yields a flatter MoO3 surface, which positively influences the growth of Ag nanostructures. Eventually, an almost homogeneous, smooth, and continuous surface morphology of the ultrathin Ag films with a thickness of 6.5 nm was obtained. By employing air-annealed MoO3 bottom layer, the MoO3 (200 °C, 10 min)/Ag (6.5 nm)/MoO3 TCF had higher optical transmittance (Tav = 83.6%) and lower sheet resistance (Rs = 6.5 Ω/sq) than unannealed MAM or commercial ITO TCFs, thereby obtaining the higher value of figure of merit (FTC = 2.6 ×10−2 Ω−1). When used as the transparent electrode in organic solar cells (OSCs), the improved optoelectrical properties of the MoO3 (200 °C, 10 min)/Ag (6.5 nm)/MoO3 electrode result in increased short-circuit current density (Jsc = 2.27 mA cm−2) and fill factor (FF = 54.8%) of OSCs in comparison to devices based on unannealed MAM and ITO electrodes, leading to an improvement in power conversion efficiency (PCE = 0.62%). From the results of photocurrent measurements, air annealing MoO3 increases exciton generation in active layers and reduces the carrier back-transfer induced recombination at the anode contact, yielding the enhanced photovoltaic performance.

SnO2 Films Elaborated by Radio Frequency Magnetron Sputtering as Potential Transparent Conducting Oxides Alternative for Organic Solar Cells

Transparent conducting oxides (TCOs) are a crucial component of solar cells. Tin-doped indium oxide (ITO) is the most employed TCO, but the scarcity and high price of indium induce a search for lower-cost TCOs with equivalent properties as substitutes. Tin dioxide (SnO2) films have many advantages, such as rich sources of material, low prices, and nontoxicity. SnO2 films present a high visible-light transmittance, near-infrared light reflectivity, and excellent electrical properties. They also have a higher chemical and mechanical stability compared to ITO. The aim of this work is to elaborate SnO2 films by radio frequency (RF)-magnetron sputtering in order to use them as electrodes for organic solar cells (OSCs). The SnO2 films were deposited on glass, SiO2, and quartz substrates in a mixed environment of Ar and O2. X-ray diffraction (XRD) measurements show that the as-deposited SnO2 films are polycrystalline with a cassiterite tetragonal structure. Scanning electron microscopy (SEM) analysis showed that the films are homogeneous, continuous, and nanostructured. The electrical resistivity and average optical transmittance of the samples are about 10–3 Ω.cm and over 80%, respectively. The estimated optical band gap (Eg) is around 4.0 eV, while the work function (WF) of the films is around 5.0 eV. The SnO2 films are used as electrodes for inverted OSCs, using poly(3-hexylthiophene-2,5-diyl): [6,6]-phenyl-C60-butryric acid methyl ester (P3HT:PC60BM) as the active layer. The device’s open-circuit voltage (VOC) and short-circuit current density (JSC) are similar to those obtained for the inverted OSCs employing ITO as the same electrode. Even if the achieved power conversion efficiency (PCE) is lower compared to the value for the reference OSC with an ITO electrode, these results are promising and place SnO2 TCO as a potential candidate to replace ITO.

Highly Stable Graphene‐Based Flexible Hybrid Transparent Conductive Electrodes for Organic Solar Cells

AbstractFlexible transparent conductive electrodes (TCEs) are an essential part of flexible electronic and energy devices. As a promising alternative to ITO (In2O3:Sn), silver nanowire has poor environmental stability and adhesion, which limits its development. Herein, transition metal carbides and carbonitrides called MXene are inserted between silver nanowires and graphene grown by chemical vapor deposition to improve the conductivity, adhesion, roughness, and stability of the electrode. Nanosheets fill the voids of the network and connect the nanowires with graphene to provide more conductive channels. In addition, due to the solvent evaporation effect and thermal effect in the preparation process, the nanowire junctions are welded together. Based on the unique structure, the proposed composite TCE shows low sheet resistance (18.1 Ω sq−1) and high optical transmittance (88.1% at 550 nm). Furthermore, compared to the reference samples, the composite TCEs demonstrate stable electrical performances under different environmental conditions, including thermal environment, exposures to air for 80 days, and bending for 2000 cycles. Finally, flexible organic solar cells (OSCs) are prepared using the composite TCEs, which show comparable efficiency to that of ITO‐based OSCs. Therefore, the flexible transparent electrodes are expected to be applied in solar cells, organic light‐emitting diodes, and a broader range.

Highly Reflective and Low Resistive Top Electrode for Organic Solar Cells and Modules by Low Temperature Silver Nanoparticle Ink

One of the issues that have caused a wide performance gap between commercially available organic photovoltaic (OPV) modules and the hero cells in literature lies in the lack of printable and roll‐to‐roll process compatible high‐performance top electrodes. This work takes an unorthodox approach to this issue by developing a printable silver nanoparticle (AgNP) film top electrode that can achieve a similar performance as evaporated ones (EvapAg). It illustrates the developmental process from ink formulation to the critical processing conditions that are tailored for OPV devices procedurally. The resultant cells and modules with AgNP electrodes have achieved almost the same power conversion efficiencies (≈90%) as those with evaporated silver electrodes, as demonstrated for multiple material systems, printing methods, as well as layouts. Under low light condition, AgNP cells perform even significantly better than EvapAg ones, due to their lower leakage currents. More importantly, this work has demonstrated that fully printed OPV modules can achieve similar performance as small scale OPV cells with evaporated electrodes when both the electrical and optical performance of their top electrodes are comparable. With the latest generation of materials, this approach offers an attractive alternative for manufacturing of highly efficient OPV modules at large scale.

Solution‐Processed Silver Nanowire as Flexible Transparent Electrodes in Organic Solar Cells

AbstractOrganic solar cells (OSCs) have attracted much attention due to their advantages in fabricating flexible and semi‐transparent devices. Especially, the light weight, flexibility and spectral adjustability make OSCs superior to silicon, perovskite and other thin film based solar cells in applications of integrated photovoltaic devices and wearable electronics. In flexible and semi‐transparent OSCs, transparent conducting electrodes (TCEs) play a key role in obtaining high performances. Among various TCEs, silver nanowire (AgNW) has become a promising candidate due to its low sheet resistance, high optical transparency, excellent mechanical flexibility and solution processability. In this article, we review the recent advances in AgNW‐based TCEs and their applications in the field of OSCs. Firstly, we introduce the general properties of AgNW, including optoelectronic and mechanical characteristics. Secondly, the preparation methods of AgNW are discussed, along with some approaches on the optimization of AgNW to overcome the shortcomings of TCEs. Thirdly, we discuss the applications of AgNW as TCEs in fabricating flexible and semi‐transparent OSCs, including the use of AgNW as bottom and top electrodes. Finally, we point out the challenges in AgNW‐based TCEs and suggest several guidelines for preparing AgNW so as to meet the demands for the practical use of OSCs.

A metal chelation strategy suppressing chemical reduction between PEDOT and polyethylenimine for a printable low-work function electrode in organic solar cells

Zinc ion chelation on PEIE can effectively suppress the chemical reaction between PEIE and PEDOT:PSS. PEDOT:PSS/PEI-Zn is an efficient electron-collecting electrode for organic solar cells.

Metallic amorphous alloy for long-term stable electrodes in organic sensors and photovoltaics

Amorphous metallic alloy, i.e. metallic glass (MG), is a metal without long-range ordered atomic arrangements. The unique structural property of MGs contributes to the superior mechanical and chemical properties to that of conventional metals. In this research, the unique characteristics of MG is considered for fabrication of long-term stable thin film strain sensors and the electrode for organic solar cells. MG thin film with zirconium (Zr) based composition exhibited encouraging results on strain sensing, showing high mechanical stability with reversible resistive response under the applied strain by bending. Furthermore, MG thin films with aluminum (Al) based composition exhibited high chemical stability, which contributed to the organic solar cell's stable operation without significant degradation in performance. Thus, the results suggest that MG is a promising material to realize long-term sustainable organic photovoltaic device. • Newly designed metallic glasses (MGs) of zirconium (Zr) and aluminum (Al) were investigated for organic thin film devices. • Zr-based MG exhibited improved stable resistive response with respect to exerted strains. • Al-based MG was sputtered onto MoO x layer for long-term stable photovoltaic operations. • MG electrodes’ superior mechanical and chemical stability contribute to enhanced reliability of the flexible devices.

Fluorine doped tin oxide as an alternative of indium tin oxide for bottom electrode of semi-transparent organic photovoltaic devices

Indium tin oxide (ITO) is commonly used as the transparent bottom electrode for organic solar cells. However, it is known that the cost of the ITO is quite high due to the indium element, and in some studies ITO coated glass substrate is found to be the most expensive component of device fabrication. Moreover, indium migration from ITO can cause stability issues in organic solar cells. Nevertheless, the use of ITO as the bottom electrode is still dominating in the field. Here, we explore the possibility of using fluorine doped tin oxide (FTO) as an alternative to ITO for the bottom electrode of organic solar cells particularly on semi-transparent cells. We present side-by-side comparisons on their optical, morphological and device properties and suggest that FTO could be more suitable than ITO as the bottom electrode for glass substrate based organic photovoltaic devices.