Layer In Polymer Solar Cells Research Articles

Bridging for Carriers by Embedding Metal Oxide Nanoparticles in the Photoactive Layer to Enhance Performance of Polymer Solar Cells

Carrier collection and light absorption is a couple of contradiction for polymer solar cells (PSCs) because of the limited carrier mobility and optical absorption coefficient for the organic active layers. In this article, the concept of “bridging for carriers” is introduced by embedding metal oxide (ZnO for electrons and NiO x for holes in this study) nanoparticles into the photoactive layer of PSCs to improve exciton separation, enhance carrier transport, reduce electron–hole recombination and thus facilitate carrier collection. It is found that ∼57.6% increase in the power conversion efficiency, i.e., from 1.98% to 3.12% for the optimal addition of ZnO and NiO x into the active layer of the P3HT:PC61BM blend is achieved as compared with the control case without adding ZnO and NiO x nanoparticles. In combination with the simple hydrothermal method of preparing these metal oxide nanoparticles, this study is believed to provide valuable contribution to explore facile approaches to address the contradiction of carrier collection and light absorption for PSCs by bridging for carriers in the photoactive layer.

Improving light harvesting and charge extraction of polymer solar cells upon buffer layer doping

It is an important strategy to improve the performance of polymer solar cells (PSCs) by incorporating metal nanoparticles into functional layers. Herein, gold (Au)@titanium dioxide (TiO2) plasmonic core-shell nanoparticles (PCSNPs) are synthesized and doped into zinc oxide (ZnO) as hybrid electron transport layer in PSCs. Improved light trapping and electrical conductivity are achieved through localized surface plasma resonance of Au@TiO2 PCSNPs. As a result, the short-circuit current density is apparently enhanced, while remaining the unchanged open-circuit voltage. The maximum PCE of 8.801% is obtained when 1.5 wt% Au@TiO2 PCSNPs are introduced into the ZnO layer. This study provides a new inspiration for the development of high efficiency PSCs.

Influences of synthesis parameters on the physicochemical and electrochemical characteristics of reduced graphene oxide/Pt nanoparticles as hole transporting layer in polymer solar cells

P-type nanocomposites of reduced graphene oxide/Pt nanoparticles (NPs), rGO/Pt(NPs), were synthesized through in-situ crystallization method and applied as a novel hole transporting layer (HTL) in polymer solar cells (PSCs). Three types of rGO/Pt NPs nanocomposites were synthesized by applying ethylene glycol (EG), sodium citrate (SC) and ascorbic acid (AA) as reducing agents through the in-situ crystallization method. The physicochemical and electrochemical characteristics of rGO/Pt(NPs) nanocomposites were compared to investigate the influences of the reducing agent type. Results revealed that the reducing agent type greatly affects the elimination level of oxygen-containing functional groups from GO nanosheets, the structural disorders induced in the resulting rGOs, and the size and the dispersion homogeneity of Pt NPs deposited onto the rGO nanosheets. This led to considerable changes in the electrical conductivity and the charge transfer resistance of the prepared nanocomposites. The rGO/Pt(NPs) sample synthesized using EG showed the lowest sheet resistance of 15 kΩ/sq, the lowest charge transfer resistance of 81 Ω and the highest flat-band potential (UF) of -4.82 eV. The PSCs prepared based on this sample exhibited 210 % and 35 % enhancement in PCE compared to the PSCs fabricated based on rGO/Pt(NPs) synthesized by SC and AA, respectively, due to easier charge extraction/collection. The PCE of this device was also about 10 % higher than that achieved for the reference PSC prepared using PEDOT:PSS.

Performance improvement of polymer solar cells with binary additives induced morphology optimization and interface modification simultaneously

Active layer morphology optimization and electrode buffer layer interface modification are commonly used strategies in improving the performance of polymer solar cells (PSCs). In this study, we prepared PTB7: PC71BM bulk heterojunction PSCs with 1,8-diiodooctane (DIO) and polyethylene glycol (PEG) additives, and studied the influence of binary additives on exciton dissociation, charge transport and charge extraction. DIO facilitates donor/acceptor phase separation for efficient exciton dissociation and charge transport. The migration of PEG from active layer to the PEDOT:PSS layer improves the crystallinity of PTB7, optimizes charge transport pathway, and enhances the conductivity of PEDOT:PSS layer. With the combined advantages of binary additives in active layer morphology optimization and anode buffer layer modification, the device exhibits a high short-circuit current density of 20.03 mA/cm2 and an improved power conversion efficiency. Binary additive provides a promising method to optimize active layer morphology and improve interfacial buffer layer of PSCs simultaneously.

In situ synthesis of gold/silver nanoparticles and polyaniline as buffer layer in polymer solar cells

A new class of hole transport layer (HTL), which is composed of gold (Au) and silver (Ag) nanoparticles (NPs), in situ synthesized with polyaniline (PANI), has been used in polymer solar cells (PSCs). Optimum metal NPs addition showed sheet resistance and transparency of 6 × 105–4.9 × 105 (Ω/sq) and 76–81%, for Au and Ag nanoparticles respectively. The effect of simultaneous addition of Au and Ag NPs (Au10Ag10PANI) were also verified and showed sheet resistance and transparency of 4.6 × 105(Ω/sq) and 77%, respectively. Impedance spectroscopy (IS) revealed charge transport improvement in Au10Ag10PANI-based PSCs and power conversion efficiency (PCE) was enhanced 74% in comparison with PEDOT:PSS-based devices. Incident Photon-to-electron Conversion Efficiency (IPCE) analysis was performed and calculated Jsc from IPCE was almost the same as Jsc calculated from current-voltage analysis. The improvement is mainly related to enhancing exciton generation, improved extraction, higher conductivity and broader light absorption compared with device containing single nanoparticles, which leads to an increase in short-circuit current. High conductivity, transparency and facile method of synthesis can make the proposed materials as a qualified alternative for PEDOT:PSS in the future.

Effect of low temperature synthesis of carbon nanotube nanocomposite on the photovoltaic performance of anode buffer layer in polymer solar cells

Today’s solar cells are simply not efficient enough and are currently too expensive to manufacture for large-scale electricity generation. However, potential advancements in nanotechnology may open the door to the production of cheaper and slightly more efficient solar cells. This research is based on the study of photovoltaic properties of low temperature synthesized carbon nanotube (CNT) nanocomposite as an anode buffer layer for the PEDOT:PSS based polymer solar cells. CNT was synthesized using simple and cost effective method at low temperature. The structural and optical properties of prepared CNT samples were characterized using X-ray diffraction (XRD) analysis, Fourier Transform Infrared (FTIR) spectroscopy, Scanning Electron Microscopy (SEM) and UV spectroscopy. CNT/PEDOT:PSS nanocomposite solutions was prepared and spin coated on a cleaned glass substrate at different spin coating speed, the fabricated buffer layer thin film devices were annealed from 100 °C to 500 °C, their optical and electrical properties were then analyzed. The XRD of synthesized CNTs nanoparticles show diffraction pattern which exhibit tetragonal structure and FTIR shows functional group of carbon nanotube. The SEM image showed that the obtained sample maintained tubular structure, cluster at 20 nm but properly dispersed at 100 nm. The optical studies of the films show an increase in absorbance as the annealing temperature increases. The photovoltaic performance of the polymer solar cell showed an improved efficiency of 6.44 % for optimized device. It is deduced from this work that low temperature synthesized CNT nanocomposite demonstrated better performance as anode buffer layer for high efficient polymer solar cells.

Natural extraction from spinach leaves as efficient modifier for ZnO based electron transporting layer in polymer solar cells

Abstract In this work, natural extraction (NE) from spinach leaves is used as modifier for ZnO based electron transporting layer (ETL) in polymer solar cells (PSCs). And NE modifying decreased the work function of ZnO film, smoothed the surface of ZnO and enhanced the charge carrier extraction, resulting in much improved devices performance. The device founded on ZnO/NE ETL with PCE-10:PC71BM as the photoactive layer attained PCE (power conversion efficiency) = 9.41% (18.51% enhancement compared with that for device based on pure ZnO ETL), suggesting that NE is an interesting candidate as efficient modifier for ETL in PSCs.

Enhanced carrier mobility and power conversion efficiency of organic solar cells by adding 2D Bi2OS2

Although polymer solar cells (PSCs) have many advantages, they have obtained great progress in the two decades, the low charge carrier mobility still restricts performance progress of PSCs. Two-dimensional (2D) Bi-based semiconductor nanomaterial (Bi2OS2) can be a potential material for improving the charge carrier mobility in the active layer of PSCs, because it exhibits a high carrier mobility, suitable band gap, wide absorption range, and good stability. In this work, we synthesize the 2D Bi2OS2 nanomaterial and incorporate it into active layer of PSCs as a third component for the first time. By introduction 1 wt% 2D Bi2OS2 nanomaterial into the PSCs, the power conversion efficiency (PCE) of PSCs can be obviously improved by more than 17% comparison with binary PSCs (from 10.51% to 12.31%). The enhancement of PCE is mainly due to the improving of charge transport, surface morphology, and crystallization of active layer. It is worth noting that the 2D Bi2OS2 play the role of the heterogeneous nucleation in the active layer, resulting in the enhanced crystallization of PBDB-T and ITIC. These results not only provide a way to improve the performance of PSCs, but also show that the 2D Bi2OS2 nanomaterial has great potential application in the PSCs.

Small-molecule electrolytes with different ionic functionalities as a cathode buffer layer for polymer solar cells

Small-molecule electrolytes were designed and synthesized as the cathode interlayer in inverted polymer solar cells.

Design and synthesis of an amino-functionalized non-fullerene acceptor as a cathode interfacial layer for polymer solar cells

A non-fullerene acceptor with amino groups can be used as a cathode interlayer to enhance the photovoltaic performance.

Hybrid ZnO Electron Transport Layer by Down Conversion Complexes for Dual Improvements of Photovoltaic and Stable Performances in Polymer Solar Cells

Polymer solar cells (PSCs) have shown excellent photovoltaic performance, however, extending the spectral response range to the ultraviolet (UV) region and enhancing the UV light stability remain two challenges to overcome in the development of PSCs. Lanthanide down-conversion materials can absorb the UV light and re-emit it at the visible region that matches well with the absorption of the active layer material PTB7-Th (poly[[2,6′-4,8-di(5-ethylhexylthienyl)benzo[1,2-b;3,3-b]dithiophene][3-fluoro-2[(2-ethylhexyl)carbony]thieno[3,4-b]thiophenediyl]]) and PBDB-T-2F, thus helping to enhance the photovoltaic performance and UV light stability of PSCs. In this research, a down-conversion material Eu(TTA)3phen (ETP) is introduced into the cathode transport layer (ZnO) in PSCs to manipulate its nanostructure morphology for its application in hyperfine structure of PSCs. The device based on the ZnO/ETP electron transport layer can obtain power conversion efficiencies (PCEs) of 9.22% (PTB7-Th–PC71BM ([6,6]-phenylC71-butyric acid methyl ester) device) and 13.12% (PBDB-T-2F–IT-4F device), respectively. Besides, in the research on PTB7-Th-PC71BM device, the stability of the device based on ZnO/ETP layer is prolonged by 70% compared with the ZnO device. The results suggest that the ZnO/ETP layer plays the role of enhanced photovoltaic performance and prolonged device stability, as well as reducing photo-loss and UV degradation for PSCs.

Solution‐Processable 2D α‐In2Se3 as an Efficient Hole Transport Layer for High‐Performance and Stable Polymer Solar Cells

Herein, a 2D α‐In2Se3 nanosheet, a binary III–VI group compound semiconductor, is fabricated by liquid‐phase exfoliation method, and the photoelectric properties of α‐In2Se3 material are investigated in depth. It is found that α‐In2Se3 film exhibits significant conductivity, outstanding optical transmission, and a suitable work function. Combined with its smooth surface and preferable hydrophobicity, α‐In2Se3 film can efficiently facilitate hole transporting in the polymer solar cells (PSCs). Due to the aforesaid advantages, a 2D α‐In2Se3 nanosheet is used as a hole transport layer (HTL) in conventional PSCs for the first time, and a relatively high power conversion efficiency (PCE) of 9.58% is achieved with the structure of ITO/α‐In2Se3/PBDB‐T:ITIC/Ca/Al, which is comparable with poly(3,4‐ethylenedioxythiophene): poly(styrenesulfonate) (PEDOT:PSS)‐based devices (9.50%). Interestingly, it is demonstrated that the α‐In2Se3 film possesses excellent thermal stability in the range from room temperature to 280 °C, and a PCE of 9.35% is achieved without annealing treatment of α‐In2Se3 film, which exhibits a great potential of α‐In2Se3 for an annealing‐free approach. Furthermore, the incorporation of α‐In2Se3 HTL also remarkably enhances the long‐term stability of PSCs compared with PEDOT:PSS‐based devices. So, the results show that 2D α‐In2Se3 is a promising candidate to be an efficient and stable hole‐extraction layer.

Recent Progress in Carbon-Based Buffer Layers for Polymer Solar Cells.

Carbon-based materials are promising candidates as charge transport layers in various optoelectronic devices and have been applied to enhance the performance and stability of such devices. In this paper, we provide an overview of the most contemporary strategies that use carbon-based materials including graphene, graphene oxide, carbon nanotubes, carbon quantum dots, and graphitic carbon nitride as buffer layers in polymer solar cells (PSCs). The crucial parameters that regulate the performance of carbon-based buffer layers are highlighted and discussed in detail. Furthermore, the performances of recently developed carbon-based materials as hole and electron transport layers in PSCs compared with those of commercially available hole/electron transport layers are evaluated. Finally, we elaborate on the remaining challenges and future directions for the development of carbon-based buffer layers to achieve high-efficiency and high-stability PSCs.

Molecular Engineering on Bis(benzothiophene-S,S-dioxide)-Based Large-Band Gap Polymers for Interfacial Modifications in Polymer Solar Cells.

The development of effectively universal interfacial materials for both conventional and inverted polymer solar cells (PSCs) plays a very crucial role in achieving highly photovoltaic performance and feasible device engineering. In this study, two novel alcohol-soluble conjugated polymers (PBSON-P and PBSON-FEO) with bis(benzothiophene-S,S-dioxide)-fused aromatics (FBTO) as the core unit and amino as functional groups are synthesized. They are utilized as universal cathode interfacial layers for both conventional and inverted PSCs simultaneously. Ascribing to the enlarged conjugated planarity and higher electron affinity for an FBTO unit, both PBSON-P and PBSON-FEO exhibit versatile electron-transporting abilities. They show wide band gaps that are important for light absorption in inverted PSCs, at which point PBSON-P and PBSON-FEO are more progressive than some of the reported small band gap cathode interfacial materials. Importantly, PBSON-P and PBSON-FEO display deep highest occupied molecular orbital energy levels, which can block holes at the cathode and thus increase the fill factor. As a result, both conventional and inverted PSCs using PBSON-P and PBSON-FEO as cathode interlayers realize high photovoltaic performance. Therefore, this series of novel polymers are amphibious cathode interfacial materials for high-performance conventional and inverted PSCs.

New Antimony-Based Organic-Inorganic Hybrid Material as Electron Extraction Layer for Efficient and Stable Polymer Solar Cells.

Hybrid organic-inorganic materials are a new class of materials used as interfacial layers (ILs) in polymer solar cells (PSCs). A hybrid material, composed of antimony as the inorganic part and diaminopyridine as the organic part, is synthesized and described as a new material for application as the electron extraction layer (EEL) in PSCs and compared to the recently demonstrated hybrid materials using bismuth instead of antimony. The hybrid compound is solution-processed onto the photoactive layer based on a classical blend, which is composed of a PTB7-Th low band gap polymer as the donor mixed with PC70BM fullerene as the acceptor material. By using a regular device structure and an aluminum cathode, the solar cells exhibited a power conversion efficiency of 8.42%, equivalent to the reference device using ZnO nanocrystals as the IL, and strongly improved compared to the bismuth-based hybrid material. The processing of extraction layers up to a thickness of 80 nm of such hybrid material reveals that the change from bismuth to antimony has strongly improved the charge extraction and transport properties of the hybrid materials. Interestingly, nanocomposites made of the hybrid material mixed with ZnO nanocrystals in a 1:1 ratio further improved the electronic properties of the extraction layers, leading to a power conversion efficiency of 9.74%. This was addressed to a more closely packed morphology of the hybrid layer, leading to further improved electron extraction. It is important to note that these hybrid EELs, both pure and ZnO-doped, also greatly improved the stability of solar cells, both under dark storage in air and under lighting under an inert atmosphere compared to solar cells treated with ZnO intermediate layers.

Nd:YAG pulsed laser production of reduced-graphene oxide as hole transporting layer in polymer solar cells and the influences of solvent type

Abstract Graphene oxide (GO) was reduced using 532 nm Nd:YAG pulsed laser irradiation (unfocused, 10 Hz repetition rate, 0.3 J/cm2) in different solvents including water, ethanol and formic acid. The obtained reduced GOs (r-GOs) were employed as hole transporting layers (HTLs) in fabrication of polymer solar cells (PSCs). The changes in the chemical composition, phase purity, optical properties, level of defects, sheet resistance (Rsh), charge transfer resistance (Rct) and morphology of r-GOs were systematically investigated using Fourier transform infrared spectroscopy, x-ray diffraction, UV–Vis and Raman spectroscopy, four-point probe, electrochemical impedance spectroscopy and atomic force microscopy. Results revealed that laser reduction of GO in formic acid led to formation of r-GOs with superior physicochemical and electrochemical characteristics, implying higher hole scavenging ability of formic acid compared to water and ethanol. The r-GOs prepared in formic acid appeared to have the lowest Rsh, Rct and surface roughness. This was attributed to the higher elimination of oxygenated functional groups in formic acid, confirmed by results obtained from physicochemical characterization of the prepared samples. Comparing the photovoltaic parameters of PSCs prepared based on r-GOs as HTL revealed that the r-GO sample produced in formic acid can act as a better HTL in P3HT:PCBM-based PSCs. This cell exhibited the highest short circuit current density (10.15 mA) and power conversion efficiency (4.02%), which was about 22% higher than that achieved for the reference PSC prepared using PEDOT:PSS as HTL. Results suggest that pulsed laser production can be considered as a promising method to produce r-GOs possessing appropriate characteristics as HTL in PSCs.

In-situ synthesis of organic-inorganic hybrid thin film of PEDOT/V2O5 as hole transport layer for polymer solar cells

Here, an organic-inorganic hybrid thin film of PEDOT/V2O5 complex was successfully obtained via an in-situ synthesis method. In detail, PEDOT buffer layer was prepared by in-situ oxidative polymerization. Then, a layer of V2O5 nanoparticles was deposited on it. V2O5 nanoparticles can closely combine with PEDOT and modifying the surface defects of PEDOT. For the control polymer solar cells (PSCs) with a PEDOT:PSS hole transport layer (HTL), a power conversion efficiency (PCE) of 3.50% is obtained. Encouragingly, a higher PCE of 3.76% is achieved for the cell using the as-prepared PEDOT/V2O5 as the HTL, which increased by 8% than that of the control device. Furthermore, the devices with PEDOT/V2O5 show a better stability than the control devices using PEDOT:PSS as HTL. The results indicate that PEDOT/V2O5 is an excellent HTL for efficient and stable PSCs.

The research and fabrication of graphene quantum dots applied as the hole transporting layer in polymer solar cells

In this report, we studied and fabricated graphene quantum dots by improved the Hummer method using NH3 reducing agent. The diameter of graphene quantum dots was approximately 6 nm, applied as the hole transport layer in organic solar cell to improve the quantum efficiency of solar cells. GQDs were very friendly with environment, made at low temperatures and might be dried into powder form and dissolved well in polar solvents. Graphene quantum dots with a 0D structure had the workfunction suistable for the conductive polymer which increased the short current (from 2.41 mA/cm2 to 4.38 mA/cm2) of polymer solar cells. They improved the performance significantly compared to conventional solar cells.

Well‐defined structures and nanoscale morphology for all‐conjugated BCPs

A series of conjugated donor–acceptor (D–A) block copolymers (BCPs) were synthesised using a one-pot Stille coupling polycondensation reaction. This involved reaction between a series of mono-bromo-functionalised Poly3-hexylthiophene (P3HT) polymers (P3HT-Br, Mn: 17, 21 and 43 kg/mol) and [N, N ′-bis (2-decyl-tetradecyl)-1,7-dibromo-3,4,9,10-perylene diimide (PBI) and [2,5-bis(trimethylstannyl)-thiophene] (T) monomers. Purification using preparative gel permeation chromatography (GPC) removed any excess P3HT and resulted in BCPs with low polydispersity index values. The P3HT-b-PBIT BCPs were characterised using 1 H-NMR and Fourier-transform infrared spectroscopy. When compared to a P3HT/PBIT polymer blend, the D–A BCP films exhibited a remarkably fine structure with a nanoscale morphology. These results indicated that these D–A BCPs have the potential for use as nanostructured active layers in polymer solar cells.

Correction to: A study on stability of active layer of polymer solar cells: effect of UV–visible light with different conditions

The original article was published with incorrect affiliation of Prof. Ibnelwaleed Hussein as well as the project number in the acknowledgment.