Application In Polymer Solar Cells Research Articles

3,4‐Dicyanothiophene—a Versatile Building Block for Efficient Nonfullerene Polymer Solar Cells

AbstractIn this contribution, a versatile building block, 3,4‐dicyanothiophene (DCT), which possesses structural simplicity and synthetic accessibility for constructing high‐performance, low‐cost, wide‐bandgap conjugated polymers for use as donors in polymer solar cells (PSCs), is reported. A prototype polymer, PB3TCN‐C66, and its cyano‐free analogue polymer PB3T‐C66, are synthesized to evaluate the potential of using DCT in nonfullerene PSCs. A stronger aggregation property in solution, higher thermal transition temperatures with higher enthalpies, a larger dipole moment, higher relative dielectric constant, and more linear conformation are exhibited by PB3TCN‐C66. Solar cells employing IT‐4F as the electron acceptor offer power conversion efficiencies (PCEs) of 11.2% and 2.3% for PB3TCN‐C66 and PB3T‐C66, respectively. Morphological characterizations reveal that the PB3TCN‐C66:IT‐4F blend exhibits better π–π paracrystallinity, a contracted domain size, and higher phase purity, consistent with its higher molecular interaction parameter, derived from thermodynamic calculations. Moreover, PB3TCN‐C66 offers a higher open‐circuit voltage and reduced energy loss than most state‐of‐the‐art wide‐bandgap polymers, without the need of additional electron‐withdrawing substituents. Two additional polymers derived from DCT also demonstrate promising performance with a higher PCE of 13.4% being achieved. Thus, DCT represents a versatile and promising building block for constructing high‐performance, low‐cost, conjugated polymers for application in PSCs.

Biaxially-extended side-chain engineering of benzodithiophene-based conjugated polymers and their applications in polymer solar cells

Abstract Herein, three benzodithiophene (BDT)-based conjugated polymers, PBDTT-FBT, P3TBDT-FBT, and PTBOT-FBT, with gradually increased biaxially-extended side-chain conjugation are synthesized. The increase in the side-chain conjugated plane is revealed to enhance the π-π* transition and intramolecular charge transfer (ICT) of the polymer to result in improved absorption at near-ultraviolet region. Besides, the electron-withdrawing ability of the large side-chain conjugation effectively downshifts the energy levels of the derived polymer. Through providing complementary absorption spectra and suitable cascade energy levels, PTBOT-FBT with the largest side-chain conjugation is demonstrated as an effective third photoactive component for both fullerene and non-fullerene-acceptor (NFA) binary bulk-heterojunction (BHJ) systems, which enables a respective improvement of 2.5% and 11.8% in PCE of the studied fullerene- and NFA-based ternary solar cell devices. Moreover, it is found that the ternary NFA-based BHJ film exhibits a more favorable morphology after adding PTBOT-FBT as compared to the fullerene-based film, suggesting the higher tolerance of the polymers with bulky sidechains in the NFA system.

Random and block conjugated polymers: a comparative study of properties

The synthesis and comparative study of four conjugated terpolymers with different arrangements for application in polymer solar cells (PSC’s) as electron donor materials is reported. The synthesized polymers were characterized by NMR, GPC, UV–Vis, TGA, FTIR, Cyclic Voltammetry (CV) and AFM. The photovoltaic devices were characterized by comparison between J(V) curves in dark and standard illumination conditions (100 µW/cm2). All materials synthesized showed good solubility and thermal stability, indicating that they are suitable for PSC's. Terpolymers (random and block) were synthesized by the Suzuki–Miyaura route varying proportion of carbazole and fluorene monomers, showing high yields. The optical and electronic characterizations showed that increasing carbazole amount decreases the polymer energy band gap, a strategic issue in order to improve photovoltaic device efficiency. The block and the random terpolymer presented similar maximum absorbance λmax, HOMO, LUMO, and band gap. Therefore, the light absorption is more influenced by composition than by differences in microstructure between random and block arrangements. Additionally, the low roughness obtained from AFM indicated a good mixture between polymers and fullerene derivative PCBM, also a key factor in the PSCs efficiency. However, the device efficiency presented not only a strong dependence on the fluorene/carbazole ratio but also on polymer structure.

Water–Alcohol-Soluble Hyperbranched Polyelectrolytes and Their Application in Polymer Solar Cells and Photocatalysis

We report here a series of water–alcohol-soluble hyperbranched polyelectrolytes, which can be used as both cathode interfacial materials (CIMs) in polymer solar cells (PSCs) and organic photocataly...

Novel benzodithiophene type low band gap polymer solar cell application and device stability study with atomic layer deposition encapsulation technique

Novel benzodithiophene type copolymer was synthesized through a solvent evaporation technique. Poly(5-(5-(4, 8-bis((2-ethylhexyl)oxy)benzo[1,2-b:4, 5-b’]dithiophen-2-yl)thiophen-2-yl)-2, 3-bis(3, 4-bis(decyloxy)phenyl)-8-(thiophen-2-yl) quinoxaline) (P-TQTBDT) solar cells were encapsulated with conventional and Atomic Layer Deposition (ALD) techniques. Characterizations of the samples were carried out via nuclear magnetic resonance (NMR), gel permeation chromotagraphy (GPC) and cyclic voltammetry (CV) techniques. Stability studies were carried out both P3HT and P-TQTBDT solar cells for comparison of commercial P3HT and our novel polymer solar cell. Our results confirm that ALD is a promising technique for encapsulation of polymer solar cell since stability of P-TQTBDT improved to 72% durability from 38% durability with ALD encapsulation technique during 300 h under AM1.5 G solar irradiation. P-TQTBDT solar cell showed higher stability (about 10%) than P3HT solar cell for both encapsulation methods. We focused on the stability of polymer solar cell can be improved with ALD encapsulation technique. Our aim was to compare P-TQTBDT polymer solar cell with P3HT solar cell. The stability results of P-TQTBDT showed that P-TQTBDT copolymer could be promising polymer to obtain very high stability of polymer solar cells.

Small energy loss and high open circuit voltage in conventional structure polymer solar cells with the mixture thin films of polyethylenimine ethoxylated and TiOX as the electron extraction layer and Ag as the cathode

One of the challenges facing the fabrication of high-performance conventional structure polymer solar cells (PSCs) is the development of new interface materials that have better air stability and charge carrier collection and transport ability. In this study, the mixture thin films of polyethylenimine ethoxylated (PEIE) and TiOX are developed as the electron extraction layer (EEL) and Ag as the cathode for the application in PSCs, replacing the Ca/Al composite cathode. Ultraviolet photoelectron spectroscopy (UPS) and space-charge-limited current (SCLC) measurements demonstrate that PEIE:TiOX/Ag shows appropriate energy levels, substantially reduced barrier potential, weakened charge carrier recombination and enhanced electron mobility. As a result, the PEIE:TiOX-based PSCs demonstrate not only an enhanced power conversion efficiency (PCE) of 10.94% but also the photovoltaic performance insensitive to the storage time, yielding an aged PCE that is 92% of the fresh PCE. This result can be further explained by the dependence of the charge carrier mobility on storage time. Our work suggests exploiting the PEIE:TiOX/Ag composite thin films as the composite cathode replacing Ca/Al thin films for successfully enhancing the photovoltaic performance and improving the stability of PSCs.

Finely Tuned Cores in Star‐Shaped Zwitterionic Molecules for Interface Engineering of High‐Performance Polymer Solar Cells

Developing stable and cheap organic cathode interlayers (OCIs; to replace metal cathode and expensive OCIs for enhancing the device stability and reducing the manufacturing cost) is an important topic for commercial applications of polymer solar cells (PSCs). Herein, four one‐step synthesized organic electron transport layers (G‐Series electron‐transport layers [ETLs]) with a novel star‐shaped molecular structure consisting of a series of different heteroatom atoms as cores and sulfobetaine ions as a terminal substituent are explored. The energy levels can be finely tuned by applying different heteroatom atoms as cores. With the conventional device structure with poly[[2,6′‐4,8‐di(5‐ethylhexylthienyl)benzo[1,2‐b;3,3‐b]dithiophene][3‐fluoro‐2[(2‐ethylhexyl) carbonyl]thieno[3,4‐b]thiophenediyl]] (PTB7‐Th) as a donor and [6,6]‐phenyl‐C71‐butyric‐acid‐methyl‐ester (PC70BM) as an acceptor, the G‐C2‐based devices exhibit a power conversion efficiency (PCE) of 8.90% with Al as the top electrode, much higher than that of the corresponding Ca/Al‐based device (7.43%). Furthermore, G‐Series‐based solar cells are also more stable than the reference device based on Ca. In addition, these easy‐to‐get ETLs can be widely suitable for other PSCs based on different active layer systems. This work not only shows a new strategy for fine‐tuning energy levels of nonconjugated zwitterionic molecules but also provides simple and stable ETLs for low‐cost and high‐performance PSCs.

TTA as a potential hole transport layer for application in conventional polymer solar cells

Abstract Hole transport layers (HTLs) play a vital role in organic solar cells (OSCs). In this work, a derivative of tetrathiafulvalene with four carboxyl groups TTA was introduced as a novel HTL to fabricate OSC with high performance. Displaying a better energy level match between HTL and active layers, the TTA based devices show a peak power conversion efficiency of 9.09%, which is comparable to the devices based on PEDOT:PSS. The favorable surface morphology recorded via atomic force microscopy, low series loss and charge recombination indicated by electrochemical impedance spectroscopy, synchronously verify the potential of TTA for application in OSCs as a valid kind of HTLs.

Chlorine Effects of Heterocyclic Ring‐Based Donor Polymer for Low‐Cost and High‐Performance Nonfullerene Polymer Solar Cells

The industrialization of polymer solar cells (PSCs) requires high‐performance devices with high efficiencies and stabilities. Although high‐performance PSCs are achieved via outstanding research into their component materials and device structures, several challenges still need to be overcome, including the synthetic complexity (SC) of producing the active material. In this study, donor polymers based on two heterocyclic rings and simple donor–acceptor structures are designed to obtain a low‐cost material for PSCs. An inexpensive and high‐performance donor polymer P(Cl) is realized by the introduction of a chlorine‐atom substitution. P(Cl), which has lower SC than commercial donor polymers, has many advantages, such as high overall yield, low number of synthetic steps, and inexpensive raw materials. Moreover, fabricated P(Cl)‐based PSCs exhibit a high power‐conversion efficiency (PCE) of 12.14%. Through the shelf protocol of the international summit on organic photovoltaics stability in dark testing‐1 (ISOS‐D‐1) measurements, superior long‐term stability is demonstrated for P(Cl)‐based devices both without and with encapsulation; their PCEs are maintained at 91% and 100% of the initial values for up to 2002 and 2858 h, respectively, under ambient conditions. Therefore, P(Cl) is a promising donor polymer for commercial PSC applications.

Enhanced stability of plasmonic polymer solar cells using ferrocenedicarboxylic acid modification

The power conversion efficiency (PCE) of polymer solar cells (PSCs) can obviously be improved by plasmon resonance effects of noble metal nanoparticles. However, incorporating noble metal such as Ag and Au nanoparticles (NPs) can usually accelerate the deterioration of PSCs due to the diffusion of noble metal atoms, which would limit the potential application of plasmonic PSCs. PSCs with ferrocenedicarboxylic acid (FDA) modified Al-doped ZnO (AZO) layer compared to pure AZO layer can synchronously increase PCEs and ultraviolet (UV) and moisture stabilities. PSCs with Ag NPs doped Al-doped ZnO (AZO:Ag) increased to 10.20% of PCE from 9.08% PCE of the reference PSCs with pure AZO layer, but show inferior stability. Furthermore, PSCs with FDA modified AZO:Ag layer obtained 10.0% of PCEs and showed superior UV durability and moisture stability. PSCs with FDA modified AZO:Ag layer respectively maintain the original PCE values of 50% and 53% exposing UV light for 13 h and aging for 9 months at RH 10%, which are obviously higher than 36% and 34% of the original PCEs of PSCs with AZO:Ag layer. The results indicate that FDA modification is an effective strategy to solve the quick deterioration of plasmonic PSCs without evidently sacrificing PCEs.

A Simple Approach to Prepare Chlorinated Polymer Donors with Low-Lying HOMO Level for High Performance Polymer Solar Cells

Both photovoltaic performance and cost of materials are the key factors for commercial application of polymer solar cells (PSCs). In this study, we designed and synthesized two new conjugated polym...

The recent progress of wide bandgap donor polymers towards non-fullerene organic solar cells

This review summarized the recent progress of highly efficient wide bandgap (WBG) donor polymers and their applications in non-fullerene polymer solar cells (NF-PSCs). A brief introduction of the background of WBG donor polymer developments was given. Then the research progress of the reported WBG donor polymers by classification of D-type and DA type molecular backbones was reviewed. The resulting structure-property correlations of the WBG donor polymers were also discussed to highlight the importance of chemical modifications, which have promoted the great progress of NF-PSC field. Finally, an outlook for future innovations of WBG donor polymers and their NF-PSCs was provided.

Simplified synthetic routes for low cost and high photovoltaic performance n-type organic semiconductor acceptors

The application of polymer solar cells (PSCs) with n-type organic semiconductor as acceptor requires further improving powder conversion efficiency, increasing stability and decreasing cost of the related materials and devices. Here we report a simplified synthetic route for 4,4,9,9-tetrahexyl-4,9-dihydro-s-indaceno [1,2-b:5,6-b’] dithiophene by using the catalyst of amberlyst15. Based on this synthetic route and methoxy substitution, two low cost acceptors with less synthetic steps, simple post-treatment and high yield were synthesized. In addition, the methoxy substitution improves both yield and efficiency. The high efficiency of 13.46% was obtained for the devices with MO-IDIC-2F (3,9-bis(2-methylene-5 or 6-fluoro-(3-(1,1-dicyanomethylene)-indanone)-4,4,9,9-tetrahexyl-5,10-dimethoxyl-4,9-dihydro-s-indaceno[1,2-b:5,6-b’] dithiophene) as acceptor. Based on the cost analysis, the PSCs based on MO-IDIC-2F possess the great advantages of low cost and high photovoltaic performance in comparison with those PSCs reported in literatures. Therefore, MO-IDIC-2F will be a promising low cost acceptor for commercial application of PSCs.

Surface roughness regulation of reduced-graphene oxide/iodine – Based electrodes and their application in polymer solar cells

The current work presents an iodine-mediated fine-tuning method for the electrical and electrochemical properties of reduced-graphene oxide (r-GO)/iodine – based electrodes for application in ITO-free polymer solar cells (PSCs). A multi-technique investigation was applied to correlate the morphological features of GO thin films (GO TFs) with iodine adsorption during the reduction process by HI vapor, electrochemical band gap, Fermi potential, charge carrier mobility and charge density of iodine/r-GO based electrodes. The electrical and electrochemical characteristics of iodine/r-GO electrodes changed considerably by alteration of their surface roughness and iodine content. Iodine/r-GO TFs with the lowest surface roughness and the highest iodine content exhibited the highest charge carrier density and Fermi potential. Electrochemical impedance spectroscopy (EIS) and quantum Hall effect (QHE) results confirmed the p-type conductivity of r-GOs/iodine-based electrodes. PSCs were fabricated using r-GO/iodine electrodes as the photo-anode to follow the influences of iodine content and surface roughness on the photovoltaic performance of the cells. PSCs prepared based on r-GO/iodine electrodes possessing the lowest surface roughness and the highest iodine content provided the lowest charge transfer resistance (Rct) and remarkably higher (∼48%) PCE.

Easily Accessible Low Band Gap Polymer for Efficient Nonfullerene Polymer Solar Cells with a Low Eloss of 0.55 eV.

Polymer solar cells (PSCs) have been attracting attention as a promising photovoltaic technology, and power conversion efficiencies (PCEs) of over 14% have been demonstrated. However, the state-of-the-art conjugated polymers for PSCs are based on the complex molecular structure that requires several steps for synthesis and purification, which impedes low materials cost for the PSCs. Thus, it is a key challenge to develop high-performance conjugated polymers with easily accessible building blocks for applications in practical PSCs. Here, a novel low band gap polymer (PFBTBOX) which comprises readily available building blocks was designed and synthesized to be used as an electron donor for PSCs. Affirmative optoelectronic properties of PFBTBOX for photovoltaic applications resulted in high PCEs up to 10.20 and 8.11% with nonfullerene and fullerene acceptors, respectively. Moreover, PFBTBOX exhibited minimal energy loss as low as 0.55 eV with a nonfullerene acceptor, indicating that PFBTBOX is a promising electron donor polymer for practical PSCs with high efficiency exceeding 10%.

Facile one-pot polymerization of a fully conjugated donor–acceptor block copolymer and its application in efficient single component polymer solar cells

A single component polymer solar cell with a CDABP film annealed at 180 °C showed a maximum power conversion efficiency of 5.28%, which is much higher than that (2.62%) of the device with the as-cast film.

Efficient organic-inorganic hybrid cathode interfacial layer enabled by polymeric dopant and its application in large-area polymer solar cells

An organic-inorganic hybrid cathode interfacial layer (CIL) was developed by doping ZnO with the naphthalene-diimide based derivative NDI-PFNBr. It was found the resulting organic-inorganic hybrid CIL showed apparently improved conductivity and could act as an effective cathode interlayer to modify indium tin oxide (ITO) transparent electrodes. As a result, by employing the blend of PTB7-Th:PC71BM as the photoactive layer, the inverted polymer solar cells (PSCs) exhibited a remarkable enhancement of power conversion efficiency (PCE) from 8.52% for the control device to 10.04% for the device fabricated with the hybrid CIL. Moreover, all device parameters were simultaneously improved by using this hybrid CIL. The improved open-circuit voltage ( V OC) was attributed to the reduced work function of the ITO cathode, whereas the enhancements in fill factor (FF) and short-circuit current density ( J SC) were assigned to the increased conductivity and more effective charge extraction and collection at interface. Encouragingly, when the thickness of the hybrid CIL was increased to 80 nm, the resulting device could still keep a PCE of 8.81%, exhibiting less thickness dependence. Considering these advantages, 16 and 93 cm2 large-area PSCs modules were successfully fabricated from the hybrid CIL by using doctor-blade coating techniques and yielded a remarkable PCE of 8.05% and 4.49%, respectively. These results indicated that the hybrid CIL could be a promising candidate to serve as the cathode interlayer for high-performance large-area inverted PSCs.

High-Performance Nonfullerene Polymer Solar Cells Based on a Wide-Bandgap Polymer without Extra Treatment.

Nonfullerene polymer solar cells (PSCs) are developed based on a fluorinated thienyl-based wide-bandgap (WBG) polymer PBBF as the electron donor and nonfullerene small molecule IDIC as the electron acceptor. PBBF exhibits a strong absorption in the range of 300-605nm with a wide optical bandgap of 2.05eV, which is complementary with that of IDIC. Meanwhile, it possesses a deeper highest occupied molecular orbital energy level of -5.52eV and a higher hole mobility of 7.3×10-4 cm2 V-1 s-1 compared to the nonfluorinated polymer PBDTT. The PSCs based on PBBF:IDIC without extra treatment show a power conversion efficiency (PCE) of 8.5% with a V oc of 0.95V, a J sc of 15.3mAcm-2 , and an FF of 58.8%, which is much higher than that of the devices based on PBDTT:IDIC (a PCE of 5.3% with a V oc of 0.88V, a J sc of 13.7mAcm-2 , and an FF of 43.9%). These results indicate that PBBF is a promising WBG polymer donor material for the photovoltaic applications in nonfullerene PSCs.

A new narrow bandgap polymer as donor material for high performance non-fullerene polymer solar cells

Abstract Polymer solar cells (PSCs) based on narrow bandgap (NBG) photovoltaic materials have attracted significant attention due to their unique applications in semitransparent devices and organic tandem solar cells. In this work, we design and synthesize a new NBG polymer PBTT based on 2-(2-ethylhexyl)-thienyl substituted benzodithiophene (BDT-T) and n-octyl-3-fluorothieno[3,4-b]thiophene-2-carboxylate (TT) as donor material for the applications in non-fullerene PSCs. Compared with the widely used NBG polymer PTB7-Th, PBTT exhibited higher film extinction coefficient of 9.27 × 10 4 cm−1, higher-lying energy levels, more ordered molecule packing and higher hole mobility of 2.13 × 10 −3 cm2 V−1 s −1. The PSCs based on PBTT: IEICO obtained a power conversion efficiency (PCE) of 9.5% with a Voc of 0.86 V, a Jsc of 17.9 mA cm−2 and a FF of 61.3%, which is significantly enhanced over that (7.3%) of the corresponding devices with PTB7-Th as donor. The significantly improved PCE could be attributed to the higher charge mobility and the improved morphology of the PBTT: IEICO blend film. These results demonstrate that PBTT is a very promising NBG polymer donor material for the applications in non-fullerene PSCs.

Fluorobenzotriazole‐Based Medium‐Bandgap Conjugated D–A Copolymers for Applications to Fullerene‐Based and Nonfullerene Polymer Solar Cells

ABSTRACTTwo new medium‐bandgap (MBG) donor–acceptor (D–A) conjugated polymers (PSTF and PDTS) with fluorobenzotriazole as an A unit and spiro[cyclopenta[1,2‐b:5,4‐b′]dithiophene‐4,9′‐fluorene] (STF) or dithienosilole (DTS) as the D unit are designed and synthesized as donor materials for polymer solar cell (PSC) applications. PSTF shows a broader absorption spectrum relative to PDTS reflecting an additional high‐energy absorption band due to the conjugated thiophene side chains on STF moiety. Compared with PDTS, PSTF exhibits weaker π–π aggregation and lower lying HOMO level. Photovoltaic properties of the PSCs reveal that either PSTF or PDTS using PC61BM as acceptor exhibits better performances than that of ITIC as acceptor, which results from the simultaneously increased Voc, Jsc, and FF of PC61BM‐based PSCs. Moreover, when combined with PC61BM and ITIC, the PSTF‐based PSCs exhibit an efficiency of 3.66% and 2.42%, respectively, which is 45% and almost 1.5 times higher than that of the PDTS‐based PSCs, respectively. This can be ascribed to the obviously improved Voc and FF of PSTF‐based PSCs benefitted from the deeper HOMO level and better active layer morphology. Our work demonstrates that using spiro‐annulated building block as donor unit to construct MBG D‐A copolymers is an alternative and effective approach for achieving efficient donor materials in PSCs. © 2018 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2018, 56, 2330–2343