PCBM Photoactive Layer 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.

Evaluation on output parameters of the inverted organic solar cells depending on transition-metal-oxide based hole-transporting materials

The study was focused on evaluating the effects of different hole transport layers (HTL) on optical, morphological, and electrical properties of organic solar cell (OSC) structures. Structuring the photoactive layer with blends of poly (3-hexylthiophene) (P3HT), and [6,6]-phenyl-C61-butyric acid methyl ester (PCBM) was practiced via spin coating technique. Transition-metal-oxides of vanadium pentoxide (V2O5), tungsten trioxide (WO3), and molybdenum trioxide (MoO3) as thin films with 10 nm thick were used for the HTL layers. The deposition of all interface layers except for P3HT:PCBM photoactive layer were radio-frequency (RF) magnetron sputtered. The surface morphological and optical properties of structures produced were examined by analyzing the UV–Vis–NIR and atomic force microscopy (AFM) measurements. The solar cell output parameters of the inverted OSCs produced were identified depending on transition-metal-oxide (TMO) based hole-transporting materials. MoO3 HTL was exhibited as smoothest interface with a root mean square (RMS) surface roughness value of 7.11 nm. The power conversion efficiency (PCE) values of OSCs with HTL of V2O5, WO3 and MoO3 were found as 1.91%, 2.04% and 2.11%, respectively. With a comparative investigation was reported that an OSC structure with HTL of MoO3 thin film providing optimal device performance in the present study might be preferred as an alternatively effective material for opto-electronic applications.

Effects of the photoactive layer properties and current transmission mechanism on optical and electrical characteristics of organic photovoltaic

The P3HT:PCBM is an important organic material as an active layer for bulk heterojunction (BHJ) organic photovoltaics (OPVs). However, in terms of photophysical properties, blend ratios of both materials and device design is an important parameter for OPVs devices. In this study, the P3HT:PCBM photoactive layer, blended in different proportions by mass (1:1, 1:0.8, 1:0.6) was coated on the PEDOT:PSS surface using the spin coater method for different devices. Finally, Al have been evaporated on the photoactive layer and the device structure completed. In other examples, 2 nm lithium fluoride (LiF) as buffer layer evaporated on the active layer for each blending ratio before metal. Optical absorption, AFM, XRD, Raman and XPS measurements were taken for each active layer and it was observed that the surface morphology and absorption characteristic of the active layer changed according to the mixing ratios. This change in active layer properties directly affected the device parameters. Electrical characterization of the six different devices performed with current density-voltage (J–V) measurement and by used a solar simulator under 100 mW/cm2 irradiation intensity. Depending on the increase in short circuit current density (Jsc) and open current voltage (Voc) values in the devices, the power conversion efficiency (PCE) of the OPVs obtained varied between 0.86% and 2.74%. This change can be attributed to the fact that the P3HT:PCBM photoactive layer forms a smoother surface morphology depending on the PCBM ratio and the series resistance decreases. Another reason for this change in PCE can be explained by the effective electron injection of the LiF layer, LiF/Al layer with lower work function and less carrier deposition at its metal-active layer interfaces. It result has been obtained that the active layer with a ratio of 1:0.8 has a more homogeneous surface morphology and the series resistance decreases, the presence of the LiF layer in the device structures increases the Jsc and Voc, accordingly the PCE increases to 2.74%. These results showed that BHJ OPV with high PCE can be obtained with the ideal mixing ratio and appropriate device design.

A comparative study on the effect of monodisperse Au and Ag nanoparticles on the performance of organic photovoltaic devices

The monodisperse Au (~5 nm) and Ag (~3 nm) nanoparticles used in this study were obtained using surfactant-assistant solvothermal methods and characterized by XRD TEM and SEM. Then, these nanoparticles were embedded into the P3HT:PCBM photoactive layer at different ratios and the effects of the nanoparticles on the performance of the organic solar cells have been studied by varying the loading percent of the NPs in the range of 0.5–2 wt%. The best solar cell composition was determined to be 1 wt% for Au NPs and 0.5 wt% for Ag NPs. Optical absorption spectrum of P3HT:PCBM, P3HT:PCBM:AuNPs and P3HT:PCBM:AgNPs active layers were obtained using UV–visible spectroscopy. The J–V plots of ITO/PEDOT:PSS/P3HT:PCBM/LiF/Al solar cells having 1.10−6 m2 OSC area and with different Au NPs and Ag NPs loading ratios in the P3HT:PCBM were obtained under air mass (AM) 1.5G illumination. Open circuit voltage, short-circuit current density, fill factor, and power conversion efficiency of the OSC were calculated. The highest PCE values were obtained as 3.35% for Au NPs and as 3.50% for Ag NPs doped devices. This increase in PCEs was explained by a plasmonic effect that stems from the metallic NPs.

Tailoring organic bulk-heterojunction for charge extraction and spectral absorption in CsPbBr3 perovskite solar cells

All-inorganic CsPbBr3 perovskite solar cells (PSCs) are promising candidates to balance the stability and efficiency issues of organic-inorganic hybrid devices. However, the large energy barrier for charge transfer and narrow spectral response are still two challenging problems for performance improvement. We present here an organic bulk-heterojunction {poly(3-hexylthiophene-2,5-diyl):[6,6]-phenyl C61 butyric acid methyl ester (P3HT: PCBM)} photoactive layer to boost the charge extraction and to widen the spectral absorption, achieving an enhanced power conversion efficiency up to 8.94% by optimizing the thickness of P3HT: PCBM photoactive layer, which is much higher than 6.28% for the pristine CsPbBr3 device. The interaction between the carbonyl group in PCBM and unsaturated Pb atom in the perovskite surface can effectively passivate the defects and reduce charge recombination. Furthermore, the coupling effect between PCBM and P3HT widens the spectral response from 540 to 650 nm for an increased short-circuit current density. More importantly, the devices are relatively stable over 75 days upon persistent attack by 70% relative humidity in air condition. These advantages of high efficiency, excellent long-term stability, cost-effectiveness and scalability may promote the commercialization of inorganic PSCs.

Hybrid P3HT: PCBM/GaN nanowire/Si cascade heterojunction for photovoltaic application

Poly (3-hexylthiophene) (P3HT) and phenyl-C61-butyric acid methyl ester (PCBM) are commonly used for the fabrication of organic photovoltaics (OPV). Efficiency limitations of OPVs could be circumvented by incorporation of inorganic nanostructures into organic blends. Again, integration of organic solar cells with well-developed silicon photovoltaic technology is ultimately desirable. In the present work, GaN nanowires with diameters of 25–50 nm and two lengths (200 and 500 nm) have been grown using molecular beam epitaxy technique. Solar-grade monocrystalline silicon wafers were used as substrates for nanowire synthesis. GaN nanostructures were incorporated into P3HT:PCBM photoactive layer in order to facilitate charge transfer between P3HT:PCBM and Si. Samples with and without nanowires were compared. Addition of nanowires led to the improvement in photovoltaic performance. Open circuit voltage has risen by 72% and short circuit current density by 200%. Series resistance has decreased 50 times, and power conversion efficiency has risen 20.7 times. Additional maxima are found in photocurrent spectrum corresponding to carriers being generated near GaN absorption edge. Moreover, external quantum efficiency peaks near GaN absorption edge, indicating the formation of current transfer channel via P3HT/GaN/Si cascade heterojunction. Mechanism explaining source of abovementioned improvement is proposed.

Manipulation of PBDT-DTNT:PCBM photoactive layers for a stability increment by core–shell and core–mantle–shell supramolecules

Two types of core–shell and core–mantle–shell supramolecules were designed based on grafted-CNTs and PBDT-DTNT chains and employed in the active layers of PBDT-DTNT:PC71BM solar cells to stabilize morphology and performance.

Production and Characterization of P3HT:PCBM Photoactive Layer Based Inverted Polymer Solar Cells

Bu çalışmada, SnO2, TiO2 ve ZnO şeffaf metal oksit ince filmler kullanılarak tersine çevrilmiş güneş hücreleri üretildi. Cam/flor katkılı kalay oksit (Glass/FTO) alttaşlar ve P3HT:PCBM polimer foto-aktif katmanı kullanılarak Cam/FTO/SnO2/Polimer/MoO3/Ag, Cam/FTO/TiO2/Polimer/MoO3/Ag ve Cam/FTO/ZnO/Polimer/MoO3/Ag güneş hücresi yapıları üretildi. Şeffaf metal oksitler püskürtme yöntemi, polimer tabası ise dönel kaplama yöntemi kullanılarak kaplandı. Kaplama sonrası SnO2, TiO2, ZnO ve P3HT:PCBM polimer katmanlarının yüzey morfolojileri Atomik Kuvvet Mikroskopu (AFM) yardımı ile analiz edildi. Ayrıca, polimer katmanının kaplama sonrasında zamana göre kuruma süreci görüntülendi. Üretilen tersine çevrilmiş güneş hücrelerinde elektron taşıma tabakası olarak görev yapan şeffaf metal oksitlerin güneş hücrelerinin fotovoltaik performansına etkileri AM 1.5 Güneş altına incelendi ve püskürtme yöntemi ile kaplanan SnO2, TiO2 ve ZnO tabakalarına sahip hücrelerin güç dönüşüm verimlilikleri sırayla %1.62, %2.78 ve %3.32 olarak ölçüldü.

Thermal stability analysis of buffered layer P3HT/P3HT:PCBM organic solar cells

Here to determine the thermal stability of buffered layer organic solar cell (BL-OSC), the effect of post anneal treatment has been studied. To investigate the effect of post annealing, the organic solar cells (OSCs) are annealed at the 120°C for different time duration. It has been observed that the BL-OSC structure exhibits the better thermal stability. Further, as the authors vary the post-annealing time duration from 0 min to 20 min, the power conversion efficiency (PCE) in the case BL-OSC drops by ~20%, whereas in conventional OSC, the PCE drops by ~35%. This annealing dependent study shows that, in conventional OSC structure an increase in phase segregation between donor and acceptor molecules reduces exciton dissociation and charge separation, this leads to sharp increase in series resistance and significant reduction in fill factor of the device. Whereas in the case of BL-OSS, there is a minimum reduction in the fill factor, which also determines the superior carrier collection and low recombination on the elevated annealing conditions. Further, the experimental results show that, in comparison with the conventional OSC structure, inserting the pure P3HT interlayer between PEDOT:PSS (hole transport layer) and P3HT:PCBM (photoactive layer) improves the PCE of the device by 34%.

In-depth investigation of the charge extraction efficiency for thermally annealed inverted bulk-heterojunction solar cells

The performance of bulk-heterojunction solar cells is significantly affected by several factors among which are the nano-morphology of the photoactive layer and the properties of interfacial layers promoting charge extraction and collection at the electrodes. In this work, we investigate the correlation between the MoOx layer thickness and the thermal annealing procedure on the device performance and on the charge extraction efficiency of inverted ITO/PEI/P3HT:PCBM/MoOx/Ag bulk heterojunction solar cells. The surface morphology of pristine and annealed P3HT:PCBM photoactive layers is examined by atomic force microscopy before and after the exposure to dichloromethane revealing that the distribution of the amorphous regions within the P3HT:PCBM layers can be related to the applied thermal annealing procedure. The chemical and molecular composition profiles in the photoactive layer and at the interfaces are investigated through depth profile analyses combining X-ray photoelectron spectroscopy and time-of-flight secondary ion mass spectrometry showing a decreasing oxidation gradient of the MoOx and low diffusion of the MoOx species in the P3HT:PCBM layer. Additionally, we show that the voltage dependent photocurrent is significantly affected by non-geminate recombination for devices with a too thin MoOx layer thickness, while applying a non-optimal thermal annealing procedure leads to increased geminate recombination of charge carriers. The highest charge extraction efficiency and device performance is reached for devices with a MoOx layer above 5 nm while thermal annealing procedure has to be applied before the deposition of the MoOx/Ag layers.

Graphene nanoplatelet doping of P3HT:PCBM photoactive layer of bulk heterojunction organic solar cells for enhancing performance

Hybrid organic photovoltaic (OPV) cells based on conjugated polymer photoactive materials are promising candidates for flexible, high-performance and low-cost energy sources owing to their inexpensive materials, cost-effective processing and ease of fabrication by simple solution processes. However, the modest PV performance obtained to date—in particular the low power conversion efficiency (PCE)—has impeded the large scale deployment of OPV cells. The low PCE in OPV solar cells is mainly attributed to the low carrier mobility, which is closely correlated to the transport diffusion length of the charge carriers within the photoactive layers. The 2D graphene material could be an excellent candidate for assisting charge transport improvement in the active layer of OPV cells, due to its huge carrier mobility, thermal and chemical stability, and its compatibility with the solution process. In this work, we report on the improvement of the optoelectronic properties and photovoltaic performance of graphene nanoplatelet (GNP)-doped P3HT:PCBM photoactive blended layers, integrated into a bulk heterojunction (BHJ) organic-photovoltaic-based device, using PEDOT:PSS on an ITO/glass substrate. First, the light absorption capacity was observed to increase with respect to the GNP content, while the photoluminescence showed clear quenching, indicating electron transfer between the graphene sheets and the polymeric matrix. Then, the incorporation of GNP into the BHJ active layer resulted in enhanced PV performance with respect to the reference cell, and the best PV performance was obtained with 3 wt.% of GNP loading, with an open-circuit voltage of 1.24 V, a short-circuit current density value of 6.18 mA cm−2, a fill factor of 47.12%, and a power conversion efficiency of about 3.61%. We believe that the obtained results contribute to the development of organic photovoltaic devices and to the understanding of the impact of sp2-bonded carbon therein.

Role of organic interfacial modifiers in inverted polymers solar cells: An in-depth analysis of perylene vs fullerene organic modifiers

Interfacial issues can significantly restrict the performance of photovoltaic devices by exacerbating the charge recombination channels, macroscopic phase separation, and providing a non-ideal contact for selective extraction of charges particularly in photovoltaic devices using organic and inorganic materials together. Organic interfacial modifiers (IMs) are often used to mitigate these issues by modifying the organic-inorganic interface. In order to extricate the role of these IMs on the photovoltaic performance we have made a comprehensive study on the application of perylene-based and fullerene small molecules having different molecular origin as organic IMs on ZnO electron extracting layers in inverted BHJs photovoltaic devices. We report an elaborate study on the electronic and surface altering properties of these IMs and correlated their effect on the different PV performance parameters of the inverted BHJ solar cells employing P3HT: PCBM photoactive layer. Our investigations demonstrate the role of these organic IMs in reducing the ZnO cathode work function and increasing its electron transportation property along with the passivation of superficial traps states present on ZnO which helps in selective extraction of charge carriers from the devices and minimize the recombination losses. These different aspects of IMs compete and their balanced effect decides the final outcome. As a result, we obtain a substantial improvement in the device performance with power conversion efficiency (PCE) of 3.0% for the C70/ZnO cathode device which shows over 60% improvement in contrast to the devices without any ZnO surface modification. The present investigation intents to exhibit the feasibility of vacuum sublimated organic small molecules in performance improvement in BHJ solar cells utilizing the ZnO ETLs and contrast their efficacy for the purpose rather than setting any benchmark device performance although the efficiencies obtained are typical for the active layer used in the study.

Photonic Flash Sintering of Ink-Jet-Printed Back Electrodes for Organic Photovoltaic Applications.

A study of the photonic flash sintering of a silver nanoparticle ink printed as the back electrode for organic solar cells is presented. A number of sintering settings with different intensities and pulse durations have been tested on both full-area and grid-based silver electrodes, using the complete emission spectrum of the flash lamps from UV-A to NIR. However, none of these settings was able to produce functional devices with performances comparable to those of reference cells prepared using thermally sintered ink. Different degradation mechanisms were detected in the devices with a flash-sintered back electrode. The P3HT:PCBM photoactive layer appears to be highly heat-sensitive and turned out to be severely damaged by the high temperatures generated in the silver layer during the sintering. In addition, UV-induced photochemical degradation of the functional materials was identified as another possible source of performance deterioration in the devices with grid-based electrodes. Reducing the light intensity does not provide a proper solution because in this case the Ag electrode is not sintered sufficiently. For both types of devices, with full-area and grid-based electrodes, these problems could be solved by excluding the short wavelength contribution from the flash light spectrum using a filter. Optimized sintering parameters allowed manufacture of OPV devices with performance equal to those of the reference devices. Photonic flash sintering of the top electrode in organic solar cells was demonstrated for the first time. It reveals the great potential of this sintering method for the future roll-to-roll manufacturing of organic solar cells from solution.

Organic Solar Cells with Boron- or Nitrogen-Doped Carbon Nanotubes in the P3HT : PCBM Photoactive Layer

Either boron- or nitrogen-doped carbon nanotubes (B- or N-CNTs) were incorporated in bulk heterojunction organic solar cells photoactive layer composed of poly(3-hexylthiophene) (P3HT) : (6,6)-phenyl-C61-butyric acid methyl ester (PCBM). The physical and chemical properties were investigated using different spectroscopic techniques. The cell performance was followed from their current-voltage (J-V) characteristics. Recombination dynamics of the photo-generated free charge carriers were investigated using micro- to milliseconds transient absorption spectroscopy (TAS). Transmission electron microscopy (TEM) images revealed the presence of cone structures and bamboo compartments in B-CNTs and N-CNTs, respectively. X-ray photoelectron spectroscopy (XPS) revealed very little boron was substituted in the carbon network and presence of pyrrolic, pyridinic, and quaternary species of nitrogen in N-CNTs.J-Vcharacteristics were found to be similar for the devices with B- and N-CNTs even though boron- and nitrogen-doped CNTs are known to have different properties, that is, p-type and n-type, respectively. TAS results showed that all devices had long lived free charge carriers but the devices with B- or N-CNTs had low power conservation efficiency and voltage.

Incorporation of SiO2 dielectric nanoparticles for performance enhancement in P3HT:PCBM inverted organic solar cells

It is well known that organic solar cells (OSCs) with inverted geometry have not only demonstrated a better stability and longer device life time but also have shown improved power conversion efficiency (PCE). Recent studies exhibit that incorporation of metal and/or semiconducting nanoparticles (NPs) can further increase the PCE for OSCs. In this present work, we have synthesized SiO2 NPs of various sizes (25, 50, 75 and 100nm) using the modified Stober method and incorporated them into P3HT:PCBM photoactive layer and ZnO based electron transport layer (ETL) in order to investigate the light trapping effects in an OSC. Absorption studies have shown a considerable increase in photo absorption in both cases. The fabricated devices demonstrated 13% increase in the PCE when SiO2 NPs are incorporated in P3HT:PCBM photoactive layer, whereas PCE was increased by 20% when SiO2 NPs are incorporated in ZnO based ETL. Mott–Schottky analysis and impedance spectroscopy measurements have been carried out to determine the depletion width and global mobility for both the devices. The possible reason for PCE enhancement and the role of SiO2 NPs in active layer and ZnO ETL are explained on the basis of the results obtained from Mott–Schottky analysis and impedance spectroscopy measurements.

Toward Stable Solar Hydrogen Generation Using Organic Photoelectrochemical Cells

Organic photoactive materials are promising candidates for the generation of solar fuels in terms of efficiency and cost. However, their low stability in aqueous media constitutes a serious problem for technological deployment. Here we present organic photocathodes for the generation of hydrogen in aqueous media with outstanding stability. The device design relies on the use of water-resistant selective contacts, which protect a P3HT:PCBM photoactive layer. An insoluble cross-linked PEDOT:PSS hole-selective layer avoids delamination of the film, and an electron-selective TiOx layer in contact with the aqueous solution electrically communicates the organic layer with the hydrogen-evolving catalyst (Pt). We developed a novel method for the synthesis of the TiOx layer compatible with low-temperature conditions. Tuning the thickness of the TiOx/Pt layer leads to a trade-off between the achievable photocurrent (∼1 mAcm–2) and the stability of the photocathode (stable hydrogen generation of 1.5 μmol h–1 cm–2 fo...

Hexagonal columnar liquid crystals as a processing additive to a P3HT:PCBM photoactive layer

Trihydrazone-functionalized cyanopyridine liquid crystals are introduced into the photoactive layer as processing additives to acquire an improved interpenetrating network and charge carrier mobility.

Elaboration of Conductive Polymer thin films (P3HT/PCBM) by spin coating method – Application for hybrid organic solar cell

The nanostructured polymer-fullerene thin film is one of the most prominent materials to make the hybrid bulk heterojunction solar cell (BHJ) with high conversion efficiency. Especially when the blend of P3HT and PCBM was used as the donor and acceptor materials. The properties of P3HT and PCBM layer in solar cell has been much studied and considered as high performance systems. One of the important factors for the high performance device is the fabrication of photo active layer with the appropriate thickness and morphology. In the ideal case, the intermolecular distance between the polymer and fullerene should be approximately 10-20 nm (the exciton diffusion distance) giving an area of extensive contact between the two phases. After the dissociation of carriers, the two polymer phases should create the path way for carriers to reach electrodes. But so far, this ideal configuration has not been published. In this work, we’ve elaborated the P3HT and PCBM photo active layers by spin coating methodon glass substrates covered ITO electrode. The rotational velocity was determined to get the necessary effective thickness of the polymer film. The annealing effect on structure, optical and electrical properties of the polymer thin film with different content of PCBM were also investigated. The experiments show the best device on electrode ITO has I-V characteristic as a photodiode and short circuit current (Isc) aboutmili-Ampere. These results demonstrate convincingly that polymer layers elaborated by spin coating method can result a good performance of the device.

Cross-linkable azido C60-fullerene derivatives for efficient thermal stabilization of polymer bulk-heterojunction solar cells

Original [60]PCBM-inspired fullerene derivatives bearing an azido functional group were synthesized. By incorporating an optimized quantity of this thermal cross-linker additive in the P3HT:[60]PCBM photoactive layer, an impressive stabilization of the bulk-heterojunction morphology at its optimal photovoltaic performance was achieved.

High-performance of PEDOT/PSS free organic solar cells on an air-plasma-treated ITO substrate.

In this work, we demonstrate the high-performance of a PEDOT:PSS free organic photovoltaic cell (OPVC) using an air-plasma modified ITO surface, followed by controlled solvent evaporation and annealing of the P3HT:PCBM photoactive layer. Ultraviolet photoelectron spectroscopy (UPS), X-ray photoelectron spectroscopy (XPS), and conductive atomic force microscopy (c-AFM) results show that the work function of ITO was increased to as high as that of PEDOT:PSS (5.2 eV) after air-plasma treatment, along with significantly enhanced electrical homogeneity. From the dynamic secondary ion mass spectroscopy (DSIMS) results, we confirm that the thermodynamic stability of the slow-dried active layer is attributed to the uniform vertical compositional distribution on the air plasma treated ITO surface, even after thermal annealing at 150 °C for 10 min. The resulting device has an open-circuit voltage of 0.65 V, a fill factor of 63%, and a power conversion efficiency of 3.38%, providing a high performance PEDOT:PSS free OPVC device.