Graphene Oxide Hole Transport Layer Research Articles

Bifunctional Graphene Oxide Hole-Transporting and Barrier Layers for Transparent Bifacial Flexible Perovskite Solar Cells

A thin graphene oxide (GO) layer has been prepared on indium tin oxide (ITO)-coated glass and plastic (polyethylene naphthalate; PEN) substrates for the application as a hole transport layer (HTL) of p–i–n-type planar perovskite solar cells. Transparent devices can be fabricated by replacing the Ag top electrode of conventional nontransparent devices with an ITO top electrode using radio frequency (RF) sputtering. The GO layer with high transmittance in the visible range exhibits excellent hole-extracting capabilities from the perovskite layer. Scanning electron microscopy (SEM) and atomic force microscopy (AFM) analyses reveal that the GO HTL uniformly covers the substrate. In addition, the GO-based devices show significantly improved long-term stability compared with the conventional poly(3,4-ethylenedioxythiophene) polystyrene sulfonate (PEDOT:PSS)-based counterparts. The enhancement in stability becomes much more apparent for flexible devices with the PEN substrate, which has been attributed to the excellent barrier properties of the GO HTL. As a result, a transparent and flexible p-i-n-type perovskite solar cell with a bifunctional GO HTL exhibits a high efficiency of 9.34% (cf. 11.39% for the glass substrate and 12.31% for the nontransparent/glass substrate) and good long-term stability.

Boosting the performance of planar inverted perovskite solar cells employing graphene oxide as HTL

The numerical simulation tool SCAPS-1D was used to analyze perovskite solar cell having the architecture ITO/ PEDOT:PSS or GO /CH3NH3PbI3-xClx/ PCBM /Au contains inverted planar hetero-junction device. In this work, we investigated the effect of inserting the Graphene Oxide (GO) as Hole Transport layer (HTL) on the performance of perovskite solar cells. Simulation results show that the use of GO as a hole transport layer is efficient. The efficiency of PSCs based on GO HTL was increased by about 1.6 % compared to the conventional PEDOT:PSS HTL device. The obtained results of optimizing the thickness of GO HTL exhibited an optimum value around 10 nm with an efficiency of 12.35 %, Voc of 1.19 V and FF of 54.8 %. We have also shown that the performance of device for high GO carrier density is a better than with low ones. In addition, increasing the temperature beyond the optimum value obtained around 320 K for both HTL materials (GO and PEDOT:PSS) has detrimental effect on the performance of the perovskite solar cells however the device is more sensitive to the temperature with PEDOT:PSS than the GO ones. The effect of band gap of GO on the performance of device is also studied. The obtained results underline the determining role playedby this parameter with an optimum value around 3.25 eV.

Acid-free polyaniline:graphene-oxide hole transport layer in organic solar cells

Emeraldine-based polyaniline (EB-PANI) was synthesized via oxidative polymerization of aniline in aqueous acid. Various aliquots of graphene oxide (GO) aqueous dispersion were added to aniline during polymerization to achieve a mass percent of GO in the PANI:GO nanocomposites of 0%, 0.49%, 2.4%, 4.9%, 7.3%, 9.8%, 12.2%, and 24.5%, respectively. TEM images of the GO taken from different locations showed that most of the GO is either a double layer or multilayer graphene sheet—although some of the locations showed a single-layer graphene sheet. Raman shift of GO presents the G band located at 1591 cm−1 and the D band located at 1321 cm−1. The thermogravimetric analysis (TGA) of the PANI:GO nanocomposite showed the evidence of existing GO in PANI. The X-ray photoelectron spectroscopy (XPS) narrow scans of EB-PANI, GO, and PANI:GO showed a maximum that is assigned to the C–C peak position (284.8 eV). The deconvolution of the C1s peak in EB-PANI reveals the presence of C–N/C=N species (285.8 eV) assigned to the amine and imine nitrogens in polyaniline. The acid-free hole transport layer (HTL) synthesized from PANI:GO composites was used in two different types of organic solar cells (OPVs), i.e., P3HT:PC60BM (1:0.6) and PCDTBT:PC70BM (1:4). The highest power conversion efficiency (PCE) as a function of GO loadings in the PANI:GO nanocomposites for P3HT:PCBM cells was for the nanocomposite PANI:GO-7.5 with an average of ~ 0.2%, where the GO loading was 7.3% w/w. Equivalently, the PCDTBT:PCBM cells exhibited the highest PCE for PANI:GO-7.5 nanocomposite (~ 0.5%), as well.

基于氧化石墨烯空穴传输层的钙钛矿太阳能电池

基于氧化石墨烯空穴传输层的钙钛矿太阳能电池

Moderately reduced graphene oxide via UV-ozone treatment as hole transport layer for high efficiency organic solar cells

Abstract This work demonstrates a new hole transport layer (HTL) via UV-ozone assisted moderate reduction of graphene oxide (GO) in organic solar cells (OSCs). The XPS and Raman measurements confirmed the successful reduction/removal of oxygen functional groups after UV-ozone treatment. Remarkably enhanced performance of the OSCs was demonstrated by the 15 min treated device with power conversion efficiency (PCE) of 4.07%, followed by the 10 min device with almost similar PCE of 4.03%, as compared to the device with untreated GO HTL exhibiting a much lower PCE of 2.80%. The significant enhancement in the device performance is attributed to the moderate reduction of oxygen functional groups, leaving behind highly conductive graphene as well as the decreased series resistance, increased shunt resistance and comparatively smooth HTL morphology. Further, it is also ascribed to enhanced short circuit current density, open circuit voltage and fill factor of UV-ozone treated GO which directly contributed to the improved PCE. Moreover, the OSCs with the UV-ozone treated GO HTL showed very good stability over the 250 h of exposure to ambient atmosphere.

Fluorinated Reduced Graphene Oxide as an Efficient Hole-Transport Layer for Efficient and Stable Polymer Solar Cells.

In this work, we have rationally designed and successfully synthesized a reduced graphene oxide (GO) functionalized with fluorine atoms (F-rGO) as a hole-transport layer (HTL) for polymer solar cells (PSCs). The resultant F-rGO has an excellent dispersibility in dimethylformamide without any surfactants, leading to a good film-forming property of F-rGO for structuring a stable interface. The recovery of conjugated C=C bonds in GO oxide after reduction increases the conductivity of F-rGO, which enhances the short-circuit current density of photovoltaic devices from 15.65 to 16.89 mA/cm2. A higher work function (WF) (5.1 eV) of F-rGO than that of GO (4.9 eV) is attributed to the fluorine group with a high electronegativity. Naturally, the better-matched WF with the highest occupied molecular orbital level of the PTB7-Th (5.22 eV) donor induces an improved energy alignment in devices, resulting in a superior open-circuit voltage of the device (0.776 vs 0.786 V). Consequently, the device with F-rGO as the HTL achieves a higher power conversion efficiency (8.6%) with long-term stability than that of the devices with GO HTLs and even higher than that of the poly(3,4-ethylenedioxythiophene)/poly(styrenesulfonate) (PEDOT/PSS) control device. These results clearly verify that the F-rGO is a promising hole-transport material and an ideal replacement for conventional PEDOT/PSS, further promoting the realization of low-cost, solution-processed, high-performance, and high-stability PSCs.

Significantly improved photovoltaic performance in polymer bulk heterojunction solar cells with graphene oxide /PEDOT:PSS double decked hole transport layer

This work demonstrates the high performance graphene oxide (GO)/PEDOT:PSS doubled decked hole transport layer (HTL) in the PCDTBT:PC71BM based bulk heterojunction organic photovoltaic device. The devices were tested on merits of their power conversion efficiency (PCE), reproducibility, stability and further compared with the devices with individual GO or PEDOT:PSS HTLs. Solar cells employing GO/PEDOT:PSS HTL yielded a PCE of 4.28% as compared to either of individual GO or PEDOT:PSS HTLs where they demonstrated PCEs of 2.77 and 3.57%, respectively. In case of single GO HTL, an inhomogeneous coating of ITO caused the poor performance whereas PEDOT:PSS is known to be hygroscopic and acidic which upon direct contact with ITO reduced the device performance. The improvement in the photovoltaic performance is mainly ascribed to the increased charge carriers mobility, short circuit current, open circuit voltage, fill factor, and decreased series resistance. The well matched work function of GO and PEDOT:PSS is likely to facilitate the charge transportation and an overall reduction in the series resistance. Moreover, GO could effectively block the electrons due to its large band-gap of ~3.6 eV, leading to an increased shunt resistance. In addition, we also observed the improvement in the reproducibility and stability.

Bulk Heterojunction Organic Solar Cells with Graphene Oxide Hole Transport Layer: Effect of Varied Concentration on Photovoltaic Performance

We report solution processable hole transport layer (HTL) for bulk heterojunction organic solar cells (BHJ OSCs) based on varied concentration of graphene oxide (GO) in aqueous suspension. The effects of varied concentration of GO at 1, 2, and 4 mg/mL on the morphological, optical, electrical, and photovoltaic properties of the OSCs have been studied. Device with the lowest concentration and least thickness of GO showed most optimized performance with a power conversion efficiency (PCE) of 2.73%, as compared to the higher concentrations, where the PCE reduced to 0.67 and 0.22% for the devices with HTL of 2 and 4 mg/mL, respectively. The remarkable reduction in the device performance at higher concentrations is mainly attributed to a drastic decrease in the short circuit current that reduced from 8.14 mA/cm2 to 2.90 and 1.10 mA/cm2 at 2 and 4 mg/mL, respectively. Similarly, the increased series resistance (Rs) from 6.89 Ω/cm2 to 9.54 and 11.51 Ω/cm2 has also reduced the device performance. Optical transmit...

Phase aggregation and morphology effects on nanocarbon optoelectronics

Controllable morphology and interfacial interactions within bulk heterojunction nanostructures show significant effects on optoelectronic device applications. In this study, a nanocarbon heterojunction, consisting of single-walled carbon nanotubes (s-SWCNTs) and fullerene derivatives, is reported by assembling/blending its structures through solution-based processes. A uniform and dense graphene oxide hole transport layer is used to facilitate the photoconversion at a near infrared (NIR) wavelength. Effective interfacial interaction between the s-SWCNTs and fullerene is suggested by the redshifted photoabsorption and nanoscale/micron-scale fluorescence, which is associated with self-assembled nanocarbon morphology.

Noncovalently grafting sulfonic acid onto graphene oxide for improved hole transport in polymer solar cells

Sulfonic acid was successfully grafted onto graphene oxide (GO) via a facile noncovalent functionalization approach using pyrene as the anchoring bridge, affording a novel water-processable sulfonic acid functionalized GO, which shows improved hole transport in polymer solar cells (PSCs) compared to that of pristine GO. The successful grafting of 1-pyrenesulfonic acid (PSA) onto the carbon basal plane of GO is confirmed by FT-IR, UV-vis and Raman spectroscopic studies. An AFM study on the film morphology of GO–PSA reveals that the PSA moiety attaches onto both sides of the single layered graphene sheets, thus prohibiting the exfoliated single-layer graphene sheets from re-stacking. Finally, GO–PSA was applied as an effective hole transport layer (HTL) in poly(3-hexylthiophene-2,5-diyl):[6,6]-phenyl-C61-butyric acid methyl ester (P3HT:PCBM) bulk heterojunction (BHJ) PSC devices. Under the optimized conditions, the ITO/GO–PSA/P3HT:PCBM/Al BHJ-PSC device has a power conversion efficiency (PCE) of 2.86%, which is enhanced by ca. 42.3% compared to that of the reference device based on pristine GO HTL (2.01%). The PCE enhancement is primarily attributed to the increase of fill factor (FF) due to the improved hole transport of GO upon PSA grafting, which results from the improved conductivity of GO upon PSA grafting and the decrease of the contact resistance between P3HT and GO because of the enhanced surface doping of P3HT by the –OSO3H groups.

Moderately reduced graphene oxide as hole transport layer in polymer solar cells via thermal assisted spray process

Polymer solar cells (PSCs) with a structure of transparent electrodes/moderately reduced graphene oxide (GO)/active layer/LiF/Al were fabricated, in which moderately reduced GO serves as a hole transport layer (HTL). The GO based HTLs were prepared using spray process, which is one of the most promising methods to demonstrate cost-efficient high speed mass production of PSCs, on hot substrate fixed at various temperatures of 100, 200, 300, and 400°C, respectively. Power conversion efficiencies (PCEs) of PSCs with sprayed GO HTLs were gradually increased as the temperature of substrate was going up and in particular PSC including sprayed GO at the highest temperature, 400°C, showed best efficiency of 3.71%. Higher performance of PSCs fabricated with GO sprayed at higher temperature was attributed to improved electrical property of GO HTL, resulting from moderate in situ reduction of GO during spray process on hot substrate.

Plasmonic organic photovoltaic devices with graphene based buffer layers for stability and efficiency enhancement

Enhancement of photoconversion efficiency (PCE) and stability in bulk heterojunction (BHJ) plasmonic organic photovoltaic devices (OPVs) incorporating graphene oxide (GO) thin films as the hole transport layer (HTL) and surfactant free Au nanoparticles (NPs) between the GO HTL and the photoactive layers is demonstrated. In particular the plasmonic GO-based devices exhibited a performance enhancement by 30% compared to the devices using the traditional PEDOT:PSS layer. Likewise, they preserved 50% of their initial PCE after 45 h of continuous illumination, contrary to the PEDOT:PSS-based ones that die after 20 h. The performance increase is attributed to the improved photocurrent and fill factor owing to the enhanced exciton generation rate due to NP-induced plasmon absorption enhancement. Besides this, the stability enhancement can be attributed to limited oxygen and/or indium diffusion from the indium tin oxide (ITO) electrode into the active layer. The industrial exploitation of composite GO/NPs as efficient buffer layers in OPVs is envisaged.