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Potential photovoltaic technology includes the newly developed dye-sensitized solar cells (DSSCs) and bulk heterojunction (BHJ) solar cells. Owing to their diverse qualities, polymers can be employed in third-generation photovoltaic cells to specifically alter their device elements and frameworks. Polymers containing phenothiazine, either as a part of their structure or as a dopant, are easy and economical to synthesize, are soluble in common organic solvents, and have the potential to acquire desired electrochemical and photophysical properties by mere tuning of their chemical structures. Such polymers have therefore been used either as photosensitizers in dye-sensitized solar cells, where they have produced power conversion efficiency (PCE) values as high as 5.30%, or as donor or acceptor materials in bulk heterojunction solar cells. Furthermore, they have been employed to prepare liquid-free polymer electrolytes for dye-sensitized and bulk heterojunction solar cells, producing a PCE of 8.5% in the case of DSSCs. This paper reviews and analyzes almost all research works published to date on phenothiazine-based polymers and their uses in dye-sensitized and bulk heterojunction solar cells. The impacts of their structure and molecular weight and the amount when used as a dopant in other polymers on the absorption, photoluminescence, energy levels of frontier orbitals, and, finally, photovoltaic parameters are reviewed. The advantages of phenothiazine polymers for solar cells, the difficulties in their actual implementation and potential remedies are also evaluated. [ABSTRACT FROM AUTHOR]

Potential photovoltaic technology includes the newly developed dye-sensitized solar cells (DSSCs) and bulk heterojunction (BHJ) solar cells. Owing to their diverse qualities, polymers can be employed in third-generation photovoltaic cells to specifically alter their device elements and frameworks. Polymers containing phenothiazine, either as a part of their structure or as a dopant, are easy and economical to synthesize, are soluble in common organic solvents, and have the potential to acquire desired electrochemical and photophysical properties by mere tuning of their chemical structures. Such polymers have therefore been used either as photosensitizers in dye-sensitized solar cells, where they have produced power conversion efficiency (PCE) values as high as 5.30%, or as donor or acceptor materials in bulk heterojunction solar cells. Furthermore, they have been employed to prepare liquid-free polymer electrolytes for dye-sensitized and bulk heterojunction solar cells, producing a PCE of 8.5% in the case of DSSCs. This paper reviews and analyzes almost all research works published to date on phenothiazine-based polymers and their uses in dye-sensitized and bulk heterojunction solar cells. The impacts of their structure and molecular weight and the amount when used as a dopant in other polymers on the absorption, photoluminescence, energy levels of frontier orbitals, and, finally, photovoltaic parameters are reviewed. The advantages of phenothiazine polymers for solar cells, the difficulties in their actual implementation and potential remedies are also evaluated.

Organic–inorganic halide perovskite solar cells (PSCs) and organic solar cells (OSCs) attract great attention as alternative renewable photovoltaic technology. The state‐of‐the‐art spiro‐OMeTAD (2,2′,7,7′‐tetrakis‐(N,N‐di‐p‐methoxyphenylamine)‐9,9′‐spirobifluorene) is the most successful hole‐transport material (HTM) employed in PSCs, whereas solution‐processed inverted OSCs generally use poly(3,4‐ethylenedioxythiophene):poly(styrenesulfonate) (PEDOT:PSS). Recently, various types of spirobifluorene‐based organic small molecules are reported to overcome the known disadvantages of spiro‐OMeTAD, such as the complex synthetic route, high synthetic cost, and requirement for hygroscopic dopants to improve the charge‐carrier mobility and device performance. Examples of spirobifluorene‐based molecules are also reported as alternative HTMs in inverted OSCs to exceed the drawbacks of PEDOT:PSS, such as acidity and batch‐to‐batch reproducibility. These features significantly limit spiro‐OMeTAD and PEDOT:PSS for large‐scale application in the future. Herein, an overview of recent developments in spirobifluorene organic small molecules as HTM in PSCs and OSCs is provided by focusing on synthetic and electrical features. Finally, the further research directions are discussed to develop novel spirobifluorene‐based HTMs for the realization of reliable and long‐term stable photovoltaic devices. [ABSTRACT FROM AUTHOR]

Important parameters of an organic semiconductor material are the electronic band gap (Eg) and the position of highest occupied and lowest unoccupied bands versus vacuum. These bands are called valence and conduction band for inorganic semiconductors. For organic semiconductors the bands defining the band gap are often called highest occupied molecular orbital (HOMO) and lowest unoccupied molecular orbital (LUMO). One advantage of semiconducting polymers is the ability to tune the band gap and the position of HOMO and LUMO levels by molecular chemical design. The organic photovoltaic solar cells need absorbers with a smaller bandgap to maximize the power conversion efficiency of these devices. There are several chemical strategies to synthesize low band gap polymers for optoelectronic applications. In this manuscript, an updated overview on the current status of these low band gap conjugated polymers will be given. The design principles of low band gap polymers, the properties of the resulting materials, and important applications and devices realized with this material class will be briefly discussed. [ABSTRACT FROM AUTHOR]

Binary additives of 1,8-diiodooctane (DIO) and 1,3,5-trichlorobenzene (135-TCB) were utilized for preparation of poly[4,8-bis(5-(2-ethylhexyl) thiophen-2-yl)benzo[1,2-b; 4,5-b']dithiophene-2,6-diyl-alt-(4-(2-ethylhexyl)-3fluorothieno[3,4-b]thiophene-)-2-carboxylate-2-6-diyl)] (PTB7-Th) and [6,6]-phenyl C 71 butyric acid methyl ester (PC 71 BM) films for bulk heterojunction (BHJ) solar cells. The addition of binary additives of DIO 3.0 vol% + 135-TCB 2.1 vol% into PTB7-Th:PC 71 BM films exhibited nano-sized of PTB7-Th networks homogeneous distribution and smaller sizes than the film without additive and with DIO 3.0 vol%. The out-of-plane orientation of PTB7-Th:PC 71 BM films were improved by addition of binary additives and 135-TCB. A rectification ratio of the BHJ solar cells were improved by using binary additives of DIO 3.0 vol% + 135-TCB 2.1 vol%. As a consequence, fill factor (FF) and power conversion efficiency (PCE) of the device with binary additives increased up to 0.69 and 7.4% as compared with FF (0.66) and PCE (6.9%) of the device with DIO 3.0 vol%. The external quantum efficiency the device with binary additives was enhanced in the region from 550 nm to 750 nm as compared with that of the device with DIO 3.0 vol%. This result was probably caused by the improvement of PTB7-Th orientation, and phase separation between the PTB7-Th and PC 71 BM. Image 1 • Binary additives of DIO and 135-TCB were utilized for preparation of BHJ films by convective deposition method. • Phase separation between the PTB7-Th and PC 71 BM films was improved. • The out-of-plane orientation of PTB7-Th in the BHJ films was enhanced by the addition of binary additives. • The improvement of a rectification ratio of the BHJ solar cells was observed. • The photovoltaic parameters were improved by using binary additives. [ABSTRACT FROM AUTHOR]

Two conjugated thienopyrrolodione-thiophene-vinyl-thiophene (TPDTVT)-based polymers, with one of them having an additional cyano (CN) group attached to the TVT building block, are synthesized and incorporated in photovoltaic device as electron-donating materials. Both TPD-TVT and TPD-TVTCN showed good thermal stability and appropriate solubility in chlorinated solvents, but they exhibited quite different optoelectrochemical and photovoltaic properties. The stronger intermolecular interactions of TPD-TVTCN, compared to TPD-TVT, lead to enhanced aggregation in blends with PC71BM. The domain sizes within 15-20 nm and improved molecular packing in TPD-TVTCN:PC71BM blend films result in better photovoltaic performance of TPD-TVTCN:PC71BM device compared to the device employing TPD-TVT. [ABSTRACT FROM AUTHOR]

Two high bandgap benzodithiophene–benzotriazole-based polymers were synthesized via palladium-catalysed Stille coupling reaction. In order to compare the effect of the side chains on the opto-electronic and photovoltaic properties of the resulting polymers, the benzodithiophene monomers were substituted with either octylthienyl (PTzBDT-1) or dihexylthienyl (PTzBDT-2) as side groups, while the benzotriazole unit was maintained unaltered. The optical characterization, both in solution and thin-film, indicated that PTzBDT-1 has a red-shifted optical absorption compared to PTzBDT-2, likely due to a more planar conformation of the polymer backbone promoted by the lower content of alkyl side chains. The different aggregation in the solid state also affects the energetic properties of the polymers, resulting in a lower highest occupied molecular orbital (HOMO) for PTzBDT-1 with respect to PTzBDT-2. However, an unexpected behaviour is observed when the two polymers are used as a donor material, in combination with PC61BM as acceptor, in bulk heterojunction solar cells. Even though PTzBDT-1 showed favourable optical and electrochemical properties, the devices based on this polymer present a power conversion efficiency of 3.3%, considerably lower than the efficiency of 4.7% obtained for the analogous solar cells based on PTzBDT-2. The lower performance is presumably attributed to the limited solubility of the PTzBDT-1 in organic solvents resulting in enhanced aggregation and poor intermixing with the acceptor material in the active layer.

Abstract: The photovoltaic and electrical properties of organic semiconductors are characterized by their low dielectric constant, which leads to the formation of polarons and Frenkel excitons. The low dielectric constant of organic semiconductors has been suggested to be significantly influential in geminate and bimolecular recombination losses in organic photovoltaics (OPVs). However, despite the critical attention that the dielectric constant has received in literature discussions, there has not yet been a thorough study of the dielectric constant in common organic semiconductors and how it changes when blended. In fact, there have been some inconsistent and contradictory reports on such dielectric constants, making it difficult to identify trends. Herein, at first a detailed explanation of a specific methodology to determine the dielectric constant in OPV materials with impedance spectroscopy is provided, including guidelines for possible experimental pitfalls. Using this methodology, the analysis for the dielectric constant of 17 common neat organic semiconductors is carried out. Furthermore, the relationship between the dielectric constant and blend morphology are studied and determined. It is found that the dielectric constant of a blend system can be very accurately predicted solely based on the dielectric constants of the neat materials, scaled by their respective weight ratios in the blend film. [ABSTRACT FROM AUTHOR]

Combination of directional solidification and convective deposition techniques was demonstrated for preparation of organic thin-film solar cells with poly[ N -9′-heptadecanyl-2,7-carbazole- alt -5,5-(4′,7′-di-2-thienyl-2′,1′,3′-benzothiadiazole)] (PCDTBT) and [6,6]-phenyl C 71 butyric acid methyl ester (PC 71 BM) as the active layer, and 1,3,5-trichlorobenzene (135-TCB) as the solidifying reagent. The nucleation density and directional solidification of PCDTBT:PC 71 BM films were controlled by the amount of 135-TCB and the coating direction of convective deposition. We found that hole mobility and power conversion efficiency ( PCE ) of PCDTBT:PC 71 BM based solar cells can be enhanced by the addition of 135-TCB into the PCDTBT:PC 71 BM layer. Through the optimization of photovoltaic performance, 30% improvement of PCE was attained when 20 mg mL −1 of 135-TCB was used for preparation of the cell as compared to the device without 135-TCB under the atmospheric conditions. [ABSTRACT FROM AUTHOR]

Abstract: The morphology of the active layer of a bulk heterojunction solar cell, made of a blend of an electron‐donating polymer and an electron‐accepting fullerene derivative, is known to play a determining role in device performance. Here, a combination of molecular dynamics simulations and long‐range corrected density functional theory calculations is used to elucidate the molecular‐scale effects that even minor structural changes to the polymer backbone can have on the “local” morphology; this study focuses on the extent of polymer–fullerene mixing, on their packing, and on the characteristics of the fullerene–fullerene connecting network in the mixed regions, aspects that are difficult to access experimentally. Three representative polymer donors are investigated: (i) poly[(5,6‐difluoro‐2,1,3‐benzothiadiazol‐4,7‐diyl)‐alt‐(3,3′″‐di(2‐octyldodecyl)‐2,2′;5′,2″;5″,2′″‐quaterthiophen‐5,5′″‐diyl)] (PffBT4T‐2OD); (ii) poly[(2,1,3‐benzothiadiazol‐4,7‐diyl)‐alt‐(3,3′″‐di(2‐octyldodecyl)‐2,2′;5′,2″;5″,2′″‐quaterthiophen‐5,5′″‐diyl)] (PBT4T‐2OD), where the fluorine atoms in the benzothiadiazole moieties of PffBT4T‐2OD are replaced with hydrogen atoms; and (iii) poly[(2,2′‐bithiophene)‐alt‐(4,7‐bis((2‐decyltetradecyl)thiophen‐2‐yl)‐5,6‐difluoro‐2‐propyl‐2H‐benzo[d][1,2,3]triazole)] (PT2‐FTAZ), where the sulfur atoms in the benzothiadiazole moieties of PffBT4T‐2OD are replaced with nitrogen atoms carrying a linear C3H7 side‐chain; these polymers are mixed with the phenyl‐C71‐butyric acid methyl ester (PC71BM) acceptor. This study also discusses the nature of the charge‐transfer electronic states appearing at the donor–acceptor interfaces, the electronic couplings relevant for the charge‐recombination process, and the electron‐transfer features between neighboring PC71BM molecules. [ABSTRACT FROM AUTHOR]

ABSTRACT Two copolymers having D-A-D-A ( P1) and D-A ( P2) structures with quinoxaline acceptor unit and dithienosilole donor unit were synthesized and their optical and electrochemical (both experimental and theoretical) properties were investigated. The optical properties showed that these copolymers P1 and P2 exhibit optical bandgaps of 1.54 and 1.62 eV, respectively, with broader absorption profiles extending up to 800 nm and 770 nm, respectively. The electrochemical investigation of these two copolymers indicates that they exhibit suitable highest occupied molecular orbital and lowest unoccupied molecular orbital energy levels for efficient exciton dissociation and high open circuit voltage in the resultant polymer solar cells (PSCs). These copolymers were used as donors along with the PC71BM as acceptor for the fabrication of solution processed bulk heterojunction PSCs. The optimized P1:PC71BM and P2:PC71BM active layers treated with solvent vapor treatment showed overall power conversion efficiency (PCE) of 7.16% and 6.57%, respectively. The higher PCE of P1-based device as compared to P2 might be attributed to higher crystallinity of P1 and good hole mobility resulting more balanced charge transport. © 2017 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2018, 56, 376-386 [ABSTRACT FROM AUTHOR]

Two new acceptor–π(donor)–donor–π(donor)-acceptor small molecules SM1 and SM2 with benzodithiophene (BDT) donor core unit linked via phenothiazine (PTZ) donor units with 1,3–indanedione and malononitrile end capping units, respectively, have been designed and synthesized and used as electron donor along with PC 71 BM as acceptor for solution-processed bulk heterojunction organic solar cells. The influence of these end-capping groups on their thermal, optical, electrochemical properties and photovoltaic performance was investigated. After the optimization of the donor to acceptor weight ratio and solvent vapor annealing, the organic solar cells based on SM1 :PC 71 BM and SM2 :PC 71 BM active layers showed the power conversion efficiency (PCE) of 6.20% and 7.45%, respectively. Hence, the end-capping acceptor units for the two small molecules revealed a significant influence on the PCE of the organic solar cells, which resulted from differences in film absorption, molecular packing and charge transport properties. [ABSTRACT FROM AUTHOR]

We synthesized an ultra low bandgap terpolymer denoted as P containing fluorinated-fluorene attached thiadiazoloquinoxaline and benzothiadiazole acceptors and thiophene as donor in its backbone and investigated its optical and electrochemical properties. This terpolymer is used for as donor along with PC 71 BM as electron acceptor in solution processed polymer solar cells (PSCs). The P showed a shows strong absorption band from 650 nm to 1100 nm with an optical bandgap of 1.12 eV and highest occupied molecular orbital (HOMO) and lowest unoccupied molecular orbital (LUMO) energy levels of −5.25 eV and −3.87 eV, respectively. After the optimization of P to PC 71 BM weight ratio, the optimized weight ratio 1:2 in chlorobenzene (CB) solution, the PSC showed overall power conversion efficiency of 4.10% (J sc of 10.96 mA/cm 2 , V oc of 0.68 V and FF of 0.55). After the solvent additive (3 v% DIO) followed by subsequent thermal annealing (SA-TA) the PCE has been increased up to 7.54% with J sc of 16.12 mA/cm 2 , V oc of 0.65 V and FF of 0.72. The increase in the PCE is related with the enhancement in the both J sc and FF, attributed optimized nanoscale morphology of the active layer for both efficient exciton dissociation and charge transport towards the electrodes and balanced charge transport in the device, induced by the TSA treatment of the active layer. This is the highest PCE of PSCs with an energy loss about 0.47 eV with the low bandgap of 1.12 eV. [ABSTRACT FROM AUTHOR]

We report bulk heterojunction organic solar cells utilising the electron-donating polymer PffBT4T-2OD blended with the fullerene acceptor PC71BM, with cells explored based on both conventional and inverted architectures. As charge-transporting layers, we utilise the hole-transporting polymer poly (2, 3-dihydrothieno-1, 4-dioxin)-poly (styrenesulfonate) (PEDOT:PSS) in conventional device architectures, and zinc oxide (ZnO) electron-transport in inverted devices. Critically, all charge-transporting layers and the poly[(5,6-difluoro-2,1,3-benzothiadiazol-4,7-diyl)-alt- (3,3‴-di(2-octyldodecyl) 2,2'; 5',2''; 5",2‴ -quaterthiophen-5,5‴-diyl)] (PffBT4T-2OD): [6,6]-phenyl C71 butyric acid methyl ester (PC71BM) active layer blend were spray coated in air. We demonstrate champion devices having a power conversion efficiency of 8.13% and 8.43% for conventional and inverted architectures respectively. [ABSTRACT FROM AUTHOR]

Donor-acceptor (D-A) type fully conjugated block copolymer systems have been rarely reported due to the challenges in synthetic approaches to prepare well-defined low-polydispersity products. In this work, fully conjugated block copolymers are synthesized in a one-pot reaction through Stille coupling polycondensation, by utilizing the end-functional polymer copolymerization method. End-functional P3HT are copolymerized with AA (2,7-dibromo-9-(heptadecan-9-yl)-9 H-carbazole) and BB (4,7-bis(5-(trimethylstannyl)thiophen-2-yl)benzo[c][1,2,5]thiadiazole, TBT) type monomers, respectively. The orthogonal solubility between the very soluble P3HT donor and the insoluble PCDTBT acceptor block improves the purity of block copolymers as well as distinct nano-scale phase-separation compared with other reports on miscibility of donor and acceptor polymer block. Further purification via preparative GPC is carried out to remove the excess of unreacted P3HT and free PCDTBT as well as to achieve low polydispersity of block copolymers. The chemical structure of the P3HT- b-PCDTBT block copolymers are verified via H-NMR, and further confirmed by FTIR spectra. The block copolymer shows broad absorption and moderate optical band gap of 1.8 eV. Furthermore, the fully conjugated block copolymer films exhibit significant fine structures, much smoother film morphology compared to P3HT/PCDTBT polymer blends. By adding a small amount of block copolymer P3HT- b-PCDTBT as a compatibilizer into the bulk-heterojunction of P3HT:PCBM blends, polymer solar cells with an 8% increase of short circuit current ( J and 10% increase of power conversion efficiency (PCE) are achieved owing to the improvement of the active-layer film morphology. To the best of our knowledge, this is the first report on donor-acceptor type fully conjugated block copolymer as an effective ternary additive in polymer: fullerene bulk heterojunction solar cells. [ABSTRACT FROM AUTHOR]

Optical and photovoltaic properties were studied for ternary photovoltaic cells containing a traditional donor-acceptor bulk-heterojunction (BHJ) active layer modified with polymethine dye molecules in a broad range of compositions and wavelengths. An effect of composition induced optical transparency, due to the strong modification of the density of states, was observed for symmetrical compositions with approximately equal amount of components. Based on our spectroscopic ellipsometry and atomic force microscopy (AFM) studies we can suggest that the variation of the refractive index, which is significantly reduced in the visible range for ternary systems, is involved in the physical mechanism of the phenomenon. Despite of an addition of the IR absorbing component (which allows broadening of the absorption band to up to 800 nm) no improvement in the power conversion efficiency (PCE) is observed in comparison to the binary BHJ system (P3HT:PCBM). Nevertheless, we believe that further advance of the efficiency will be possible if the energy levels will be chemically designed to avoid formation of charge traps at the BHJ interface during light excitation. Such fine adjustment of the system should become possible with a proper choice of polymer:dye composition due to a high versatility of the polymethine dyes demonstrated in previous studies. [ABSTRACT FROM AUTHOR]

A novel small molecule with D1-A-D2-A-D1 structure denoted as DTS(QxHT 2 ) 2 based on quinoxaline acceptor and dithienosilone donor units was synthesized and its optical and electrochemical properties were investigated. The thin film of DTS(QxHT 2 ) 2 showed a broad absorption profile covering the solar spectrum from 350 nm to 780 nm with an optical bandgap of 1.63 eV. The energy levels estimated from the cyclic voltammetry indicate that this small molecule is suitable as donor along with PC 71 BM as acceptor for the fabrication solution processed bulk heterojunction solar cells for efficient exciton dissociation and high open circuit voltage. The organic solar cells based on optimized DTS(QxHT2)2:PC 71 BM active layers processed with chloroform and DIO/CF showed overall power conversion efficiency of 3.16% and 6.30%, respectively. The higher power conversion efficiency of the solar cell based on the DIO/CF processed active layer is attributed to enhanced short circuit photocurrent and fill factor may be related to better phase separation between donor and acceptor in the active layer and more balanced charge transport, induced by the solvent additive. The power conversion efficiency of the organic solar cell was further improved up to 7.81% based on active layer processed with solvent additive, using CuSCN as hole transport layer instead of PEDOT:PSS and mainly attributed to increased fill factor and open circuit voltage due the formation of better Ohmic contact between the active layer and the CuSCN layer. [ABSTRACT FROM AUTHOR]

We investigate a correlation between the type of solvent additives (SAs) with specific criteria such as aromatic additives (AAs) and non-aromatic additives (NAAs) and phase separation in the bulk heterojunction (BHJ) films comprising low-band gap polymer and fullerene derivatives. When AAs are used as SAs, the geometrical structures (π-π and lamellar stacking) of aggregated polymer chains do not significantly change. However, NAAs increase the lamellar stacking distance through a strong interaction with non-aromatic segments of polymers. Therefore, a well-phase separated BHJ morphology with the finer fibrils is developed, thereby leading to balanced charge mobilities and a reduced charge recombination in BHJ solar cells. Finally, the optimized solar cell exhibits a high power conversion efficiency of 7.9%. [ABSTRACT FROM AUTHOR]

Anodized TiO2 nanotubes have received much attention for their use in solar energy applications including water oxidation cells and hybrid solar cells [dye-sensitized solar cells (DSSCs) and bulk heterojuntion solar cells (BHJs)]. High surface area allows for increased dye-adsorption and photon absorption. Titania nanotubes grown by anodization of titanium in fluoride-containing electrolytes are aligned perpendicular to the substrate surface, reducing the electron diffusion path to the external circuit in solar cells. The nanotube morphology can be optimized for the various applications by adjusting the anodization parameters but the optimum crystallinity of the nanotube arrays remains to be realized. In addition to morphology and crystallinity, the method of device fabrication significantly affects photon and electron dynamics and its energy conversion efficiency. This paper provides the state-of-the-art knowledge to achieve experimental tailoring of morphological parameters including nanotube diameter, length, wall thickness, array surface smoothness, and annealing of nanotube arrays.

Herein we report on the synthesis of an N-annulated perylene diimide (PDI) disubstituted thieno[3,4-c]pyrrole-4,6-dione (TPD) molecular acceptor (PDI–TPD–PDI) by direct heteroarylation (DHA) methods. Three sets of DHA conditions that explore the effects of solvent, temperature, and catalyst were employed to find the optimal conditions for the synthesis of two PDI–TPD–PDI derivatives. We then selected one PDI–TPD–PDI for use as a non-fullerene acceptor in organic solar cell devices with the donor polymer PBDB-T. Active layer bulk-heterojunction blends were modified using several post-deposition treatments, including thermal annealing, solvent vapour annealing, and high boiling solvent additives. It was found that active layers cast from o-dichlorobenzene with a 3% v/v diphenylether additive yielded films with adequate phase separation, and subsequently gave the best organic solar cell performance, with power conversion efficiencies greater than 3%.

Bimolecular recombination in bulk heterojunction organic solar cells is the process by which nongeminate photogenerated free carriers encounter each other, and combine to form a charge transfer (CT) state which subsequently relaxes to the ground state. It is governed by the diffusion of the slower and faster carriers toward the electron donor-acceptor interface. In an increasing number of systems, the recombination rate constant is measured to be lower than that predicted by Langevin's model for relative Brownian motion and the capture of opposite charges. This study investigates the dynamics of charge generation, transport, and recombination in a nematic liquid crystalline donor:fullerene acceptor system that gives solar cells with initial power conversion efficiencies of >9.5%. Unusually, and advantageously from a manufacturing perspective, these efficiencies are maintained in junctions thicker than 300 nm. Despite finding imbalanced and moderate carrier mobilities in this blend, strongly suppressed bimolecular recombination is observed, which is ≈150 times less than predicted by Langevin theory, or indeed, more recent and advanced models that take into account the domain size and the spatial separation of electrons and holes. The suppressed bimolecular recombination arises from the fact that ground-state decay of the CT state is significantly slower than dissociation. [ABSTRACT FROM AUTHOR]

A new electron deficient monomer (PDBT) unit incorporating a weak electron accepting unit, pyrrolo[3,4- c ]pyrrole-1,3-dione (DPPD), and a strong electron accepting unit, 4,7-di(thiophen-2-yl)benzo[c][1,2,5]thiadiazole (BT), with a configuration of DPPD-BT-DPPD was prepared, and copolymerized with a benzodithiophene (BDTT) derivative to afford a new alternating ternary copolymer P(BDTT-PDBT). The estimated optical band gap ( E g ) and highest occupied/lowest unoccupied (HOMO/LUMO) molecular orbital energy levels of P(BDTT-PDBT) were 1.72 eV and −5.45 eV/−3.62 eV, respectively. A field effect transistor made from P(BDTT-PDBT) exhibited a hole mobility of 3.2 × 10 −3 cm 2 V −1 s −1 . Conventional single layer polymer solar cells (PSCs) prepared using P(BDTT-PDBT) with an additive offered a maximum power conversion efficiency ( PCE ) of 5.73% with an open-circuit voltage ( V oc ) of 0.90 V, a short-circuit current ( J sc ) of 9.73 mA/cm 2 , and a fill factor ( FF ) of 0.66. Interestingly, the PSC device prepared without an additive also showed a similar PCE of 4.84% (V oc ∼ 0.92 V, J sc ∼ 8.08 mA/cm 2 , and FF ∼ 0.65). This paper reports the preparation of an efficient ternary copolymer for polymer solar cells utilizing high energy sunlight, as well as the property modulation of an alternating binary copolymer, P(BDTT-DPPD), containing BDTT and DPPD derivatives via the insertion of a strong electron accepting BT unit on the P(BDTT-DPPD) backbone. [ABSTRACT FROM AUTHOR]

A family of porphyrins and benzoporphyrins bearing phenyl, thiophenyl, or bithiophenyl groups at their meso-positions are synthesized and systematically investigated for their potential use in bulk heterojunction solar cells (BHJ-SCs). Comparative studies of these compounds show that the introduction of the thiophenyl and bithiophenyl groups, and the extension of the porphyrin π-conjugated system significantly affect both photophysical and electrochemical properties. Binary conventional and ternary converted BHJ-SCs based on these compounds are fabricated and studied. Results show that remarkable enhancement of the device efficiency is achieved by using the thiophene-containing benzoporphyrin derivatives as additives for a poly(3-hexylthiophene) (P3HT):phenyl-C61-butyric acid methyl ester blend in the inverted BHJ-SCs. The optimum BHJ-SC exhibits a maximum energy conversion efficiency of 4.3%, corresponding to 19% enhancement of the conversion efficiency as compared with the benchmark BHJ-SCs. [ABSTRACT FROM AUTHOR]

Three novel conjugated polymers incorporating extended DADAD and DADADAD building blocks with the 5,6-bisalkoxybenzoxadiazole acceptor (A) and the electron donor (D) thiophene units were synthesized and fully characterized. The application of the benzoxadiazole instead of benzothiadiazole resulted in a significant increase in the open circuit voltage of organic solar cells based on such polymers. The best performing material delivered a decent solar light power conversion efficiency of 5.5% in organic bulk heterojunction solar cells using PC 71 BM as an electron acceptor component. The obtained results revealed a high potential of using different acceptor building blocks in the design of novel (-X-DADAD-) n polymers with tailored optoelectronic and photovoltaic properties. [ABSTRACT FROM AUTHOR]

A series of pyrrolo[3,4-c]pyrrole-1,3(2H,5H)-dione (DPPD)-based polymers incorporating different alkyl side chains on the imide nitrogen were prepared to investigate the imide-linked alkyl side chain effects on the properties of DPPD-based polymers. DPPD derivatives with heptyl, octyl, decyl and dodecyl substituents on the imide nitrogen were prepared and copolymerized with 2,6-bis(trimethyltin)-4,8-bis(2-ethylhexyloxy)benzo[1,2-b:4,5-b′]dithiophene (BDT) to offer polymers P(BDT-C 7 -DPPD), P(BDT-C 8 -DPPD), P(BDT-C 10 -DPPD), and P(BDT-C 12 -DPPD), respectively. All four polymers displayed identical optical band gaps ( E g ∼ 2.11 eV) and highest occupied/lowest unoccupied molecular orbital energy levels (HOMO/LUMO ∼ −5.39 eV/–3.28 eV). The conventional single layer polymer solar cell (PSC) fabricated with a device structure of ITO/PEDOT:PSS/polymer:PC 70 BM (1:1.5 wt%)/Al offered a power conversion efficiency ( PCE ) of 1.65%, 1.49%, 1.24%, and 0.87%, respectively. The PSC device performance was improved to 5.67%, 5.29%, 4.06%, and 2.46%, respectively, with the use of processive additive such as 1,8-diiodoocate (DIO). [ABSTRACT FROM AUTHOR]

Two small molecules denoted as K2 and K3 containing fluorine atoms at different positions of benzotriazole, with linear D1-A-D2-A-D1 configuration based on dithienosilole and fluorobenzotriazole as donor and acceptor materials, were designed and synthesized for small molecule organic solar cells. Their optical and electrochemical properties were investigated. We have used these small molecules as electron donor along with the [6,6]-phenyl C 60 butyric acid methyl ester or [6,6]-phenyl C 71 butyric acid methyl ester as electron acceptor for the fabrication of solution processed organic bulk heterojunction solar cells. High power conversion efficiency values of 6.01% and 4.57% were obtained for devices based on K2 :PC 71 BM and K3 :PC 71 BM active layers with optimized donor to acceptor weight ratios and processed with a two step annealing treatment. The efficiency of solar cells based on small molecules can be increased considerably by careful engineering and optimization of molecular structure of the blended film morphology. [ABSTRACT FROM AUTHOR]

Polymer-fullerene packing in mixed regions of a bulk heterojunction solar cell is expected to play a major role in exciton-dissociation, charge-separation, and charge-recombination processes. Here, molecular dynamics simulations are combined with density functional theory calculations to examine the impact of nature and location of polymer side-chains on the polymer-fullerene packing in mixed regions. The focus is on poly-benzo[1,2-b:4,5-b′]dithiophene-thieno[3,4-c]pyrrole-4,6-dione (PBDTTPD) as electron-donating material and [6,6]-phenyl-C61-butyric acid methyl ester (PC61BM) as electron-accepting material. Three polymer side-chain patterns are considered: i) linear side-chains on both benzodithiophene (BDT) and thienopyrroledione (TPD) moieties; ii) two linear side-chains on BDT and a branched side-chain on TPD; and iii) two branched side-chains on BDT and a linear side-chain on TPD. Increasing the number of branched side-chains is found to decrease the polymer packing density and thereby to enhance PBDTTPD-PC61 BM mixing. The nature and location of side-chains are found to play a determining role in the probability of finding PC61BM molecules close to either BDT or TPD. The electronic couplings relevant for the exciton-dissociation and charge-recombination processes are also evaluated. Overall, the findings are consistent with the experimental evolution of the PBDTTPD-PC61BM solar-cell performance as a function of side-chain patterns. [ABSTRACT FROM AUTHOR]

Two donor−acceptor low band gap polymers P1 (octyl as solubilizing group) and P2 (ethylhexyl as solubilizing group) containing fluorenylthiophene-substituted benzoditihiophene as an electron-rich unit and 3,6-bis(5-bromothiophen-2-yl)-2,5-bis(2-ethylhexyl)pyrrolo[3,4-c]pyrrole-1,4(2H,5H)-dione as an electron-deficient unit are designed and synthesized for polymer solar cells application. Compared with P2 based on ethyl hexyl group, P1 with octyl group displays well resolved vibronic shoulder peak in absorption spectra, stronger intermolecular interactions, and higher hole mobility. Polymer solar cells based on P1 and [6,6]-phenyl-C71-butyric acid methyl ester (PC71BM) exhibit a maximum power conversion efficiency of 1.78% under AM 1.5G illumination (100 mW/cm2). [ABSTRACT FROM AUTHOR]

The light intensity dependence of the main photoelectrical parameters of the nonfullerene small-molecule bulk heterojunction (BHJ) solar cells p-DTS(FBTTh2)2:perylene diimide (T1:PDI) shows that the nongeminate recombination losses play an important role in this system. A simple approach for the quantitative analysis of capacitance spectroscopy data of the organic BHJ solar cells, which allows to determine the density of free charge carriers as a function of applied bias under standard working conditions, is demonstrated. Using the proposed capacitance spectroscopic technique, the nongeminate recombination losses in the T1:PDI solar cells are quantitatively characterized in the scope of the bimolecular- and trap-assisted recombination mechanisms. Their contributions are separately analyzed within a wide range of the applied bias. [ABSTRACT FROM AUTHOR]

In this publication we show that the procedure to synthesize nanocrystals and the post-synthetic nanocrystal ligand sphere treatment have a great influence not only on the immediate performance of hybrid bulk heterojunction solar cells, but also on their thermal, long-term, and air stability. We herein demonstrate this for the particular case of spherical CdSe nanocrystals, post-synthetically treated with a hexanoic acid based treatment. We observe an influence from the duration of this post-synthetic treatment on the nanocrystal ligand sphere size, and also on the solar cell performance. By tuning the post-synthetic treatment to a certain degree, optimal device performance can be achieved. Moreover, we show how to effectively adapt the post-synthetic nanocrystal treatment protocol to different nanocrystal synthesis batches, hence increasing the reproducibility of hybrid nanocrystal:polymer bulk-heterojunction solar cells, which usually suffers due to the fluctuations in nanocrystal quality of different synthesis batches and synthesis procedures. [ABSTRACT FROM AUTHOR]

We present the synthesis and photovoltaic application of a conjugated polymer, PBDT-KTBDT, composed of two benzo[1,2- b:4,5- b′]dithiophene (BDT)-based units. In detail, PBDT-KTBDT is composed of alkoxy-substitued BDT units as the electron donating groups and alkylcarbonythienyl-substitued BDT units as the electron withdrawing moieties. The proposed polymer exhibits good solubility, sufficient thermal stability, moderate UV-vis absorption wavelength and energy levels. Solution-processed organic solar cells were fabricated using PBDT-KTBDT as an electron donor and PCBM as an electron acceptor, and a power conversion efficiency of 1.50% was obtained. Our results reveal that the copolymer with donor-donor composition is a viable candidate as a semiconductor in OPVs, and it is possible to further improve solar cells through more extensive research on these two BDT units-based materials. [ABSTRACT FROM AUTHOR]

Property modulation of 2,5-dioctylpyrrolo[3,4-c]pyrrole-1,3(2H,5H)-dione (DPPD)-based high energy converting wide band gap polymers, P(BDT-TDPPDT) and P(BDTT-TDPPDT), was studied via the incorporation of an additional DPPD unit on their repeating units. A new electron acceptor (BDPPD) unit containing two DPPD units was prepared and copolymerized with the distannyl derivatives of benzodithiophene (BDT) or 2D-conjugated benzodithiophene (BDTT) to provide two new polymers, P(BDT-BDPPD) and P(BDTT-BDPPD). The optical band gaps and highest occupied molecular orbital (HOMO)/lowest unoccupied molecular orbital (LUMO) energy levels of P(BDT-BDPPD) and P(BDTT-BDPPD) were 2.16 eV, 2.08 eV and −5.37 eV/‒3.21 eV, −5.44 eV/‒3.36 eV, respectively. The hole mobilities of P(BDT-BDPPD) and P(BDTT-BDPPD) were in the order of 10 −4 cm 2 V −1 s −1 . The polymer solar cells (PSCs) prepared with the configuration of ITO/PEDOT:PSS/P(BDT-BDPPD) or P(BDTT-BDPPD):PC 70 BM/Al gave maximum power conversion efficiencies ( PCEs ) of 2.74% and 3.63%, respectively. The insertion of a BDPPD unit instead of a TDPPDT unit on the DPPD-based polymer backbone did not affect the optical and electrochemical properties considerably. On the other hand, the new polymers, P(BDT-BDPPD) and P(BDTT-BDPPD), resulted in improved photovoltaic performances compared to the reported polymers, P(BDT-TDPPDT) and P(BDTT-TDPPDT), for the devices prepared without additives. [ABSTRACT FROM AUTHOR]

We present bulk heterojunction organic solar cells fabricated by spray-casting both the PEDOT:PSS hole-transport layer (HTL) and active PBDTTT-EFT:PC71BM layers in air. Devices were fabricated in a (6 × 6) array across a large-area substrate (25 cm2) with each pixel having an active area of 6.45 mm2. We show that the film uniformity and operational homogeneity of the devices are excellent. The champion device with spray cast active layer on spin cast PEDOT:PSS had an power conversion efficiency (PCE) of 8.75%, and the best device with spray cast active layer and PEDOT:PSS had a PCE of 8.06%. The impacts of air and light exposure of the active layer on device performance are investigated and found to be detrimental. Copyright © 2015 John Wiley & Sons, Ltd. [ABSTRACT FROM AUTHOR]

In this study, we fabricated PEDOT:PSS film with different concentrations 0–5 mg/ml of boric acid (H 3 BO 3 ) doped PEDOT:PSS film as hole collector layer. Undoped and boric acid doped PEDOT:PSS films are prepared with spin coating technique and characterized by XRD, UV, AFM, FTIR and electrical conductivity measurements. We fabricated polymer solar cells in the form of ITO/PEDOT:PSS:H 3 BO 3 /P3HT:PCBM/Al. Results show that the open-circuit voltage ( V oc ) and the fill factor (FF) increased by introducing H 3 BO 3 as dopant into the PEDOT:PSS layer due to an increase in the work function of PEDOT:PSS layer and improvement of surface roughness, respectively. The solar cells without H 3 BO 3 showed a power conversion efficiency PCE of 1.79% whereas the cells with H 3 BO 3 concentration of 1.25 mg/ml in PEDOT:PSS, showed a higher performance resulting in a PCE of 2.14% under AM 1.5G illumination. [ABSTRACT FROM AUTHOR]

Carbazole based molecules are more important in organic solar cell (OSC) applications, because carbazole derivatives have more thermal stability, high hole transporting property, more electron rich (p-type) material, higher photoconductivity, and better chemical stability. This review deals with bulk heterojunction organic solar cell (BHJ OSC) devices, structures, working principle, device characterization, perovskite type solar cell, and studies of the photovoltaic performance of carbazole based derivatives such as 2,7-carbazole, indolo[3,2- b ]carbazole containing donors (D) coupled with various acceptors (A) namely benzothiadiazole, thiazolothiazole, diketopyrrolopyrrole, and quinoxaline that are reported during the last decade and also dye-sensitized solar cell (DSSC) performance of carbazole derivatives. We will briefly outline the relationship between the structure and power conversion efficiencies (PCEs). [ABSTRACT FROM AUTHOR]

This communication presents the preliminary investigations of the activity of azomethine naphthalene diimides in organic solar cell. This study explores the photovoltaic properties of four azomethine naphthalene diimides in bulk heterojunction photovoltaic cells under an illumination of 17 mW/cm 2 . Organic solar cells in the configuration of indium tin oxide/poly(3,4-(ethylenedioxy)thiophene):poly(styrenesulfonate)/active layer/aluminum (ITO/PEDOS:PSS/active layers/Al) were constructed. Three kinds of devices which differ in the composition of active layer were fabricated. In the first type of device the active layer contains of [6,6]-phenyl-C61-butyric acid methyl ester (PCBM) with the azomethine naphthalene diimide, whereas, in the second type active layer consists of blend of poly(3-hexylthiophene-2,5-diyl) (P3HT) with the azomethine naphthalene diimide. The third type of device comprises of active layer containing P3HT and PCBM with azomethine naphthalene diimides. Compound end-capped with ethylenedioxythiophene units showed the highest value of power conversion efficiency (PCE) of 5.50%, being superior to the device based on P3HT and PCBM for which PCE of 3.88% was measured. To the best of our knowledge, first time the device based on azomethine naphthalene diimide exhibited such high value of power conversion efficiency. [ABSTRACT FROM AUTHOR]

Two new conjugated acceptor–donor–acceptor (A–π-D–π-A) compounds having a Zn-porphyrin acting as donor and linked by ethynylenes to one or two units of thienylenevinylene and capped by dicyanovinylene groups as acceptor units have been synthesized and their photophysical and electrochemical properties were investigated. These compounds were used as donor materials and PC 61 BM and PC 71 BM were used as acceptors in solution-processed bulk-heterojunction (BHJ) organic solar cells and the best photoconversion efficiency (PCE) obtained was 3.21%. [ABSTRACT FROM AUTHOR]

To investigate the property modulation of 2,5-di(2-thienyl)pyrrole (TPT)-based polymers via the incorporation of alkyl, aryl or cyano groups on the TPT unit, four new polymers namely P(BDT-AlTPTH), P(BDT-AlTPTCN), P(BDT-ArTPTH) and P(BDT-ArTPTCN) containing 4,8-bis(2-ethylhexyloxy)benzo[1,2-b:4,5-b′]dithiophene (BDT) and TPT derivatives were prepared and their opto-electrical, charge transport and photovoltaic properties were studied. The opto-electrical studies suggest that the N-aryl TPT-based polymers such as P(BDT-ArTPTH) and P(BDT-ArTPTCN) displayed redshifted absorption maxima and higher highest occupied molecular orbital (HOMO) energy levels compared to those of their corresponding N-alkyl TPT-based polymers such as P(BDT-AlTPTH) and P(BDT-AlTPTCN). On the other hand, polymers P(BDT-AlTPTCN) and P(BDT-ArTPTCN) incorporating electron-accepting cyano group on TPT backbone showed blueshifted absorption maxima and deeper HOMO energy levels compared to those of polymers P(BDT-AlTPTH) and P(BDT-ArTPTH) containing hydrogen on TPT backbone. The organic field-effect transistors (OFETs) made from the synthesized polymers suggest that the TPT-based polymers containing hydrogen on TPT backbone exhibit quite similar mobility, but the incorporation of cyano group on TPT backbone notably decrease the hole mobility. The photovoltaic studies suggest that the polymer solar cells (PSCs) made from the TPT-based polymers containing hydrogen on TPT backbone give higher power conversion efficiency (PCE) than those made from their corresponding polymers incorporating cyano group on TPT backbone. [ABSTRACT FROM AUTHOR]

We have designed, synthesized and utilized a new non-fullerene electron acceptor, 9,9′-(9,9-dioctyl-9 H-fluorene-2,7-diyl)bis(2,7-dioctyl-4-(octylamino)benzo[ lmn][3,8]phenanthroline-1,3,6,8(2 H,7 H)-tetraone) ( B2), for use in solution-processable bulk-heterojunction devices. B2 is based on a central fluorene moiety, which was capped at both ends with an electron-accepting naphthalenediimide functionality. B2 exhibited excellent solubility (>30 mg mL−1 in chloroform), high thermal and photochemical stability, and appropriate energy levels for use with the classical polymer donor regioregular poly(3-hexylthiophene). A power conversion efficiency of 1.16 % was achieved for primitive bulk-heterojunction devices with a high fill factor of approximately 54 %. [ABSTRACT FROM AUTHOR]

We synthesized two new, air-stable and environmentally friendly polyazomethines and characterized their photovoltaic and electrochemical impedance spectroscopic properties. Two polyazomethines with one (25Th-DMB) or three (2252Th-DMB) thiophene rings were synthesized and tested as donors in the active layer in solar cells. The investigated polymer solar cells contained different amounts of PCBM and PC 71 BM. The bulk heterojunction polymer solar cells were fabricated and studied, considering the architecture of the devices (i.e., LiF, TiO 2 , and TiO 2 :Ag) and the fabrication conditions (i.e., air, inert gas, and annealing). The highest power conversion efficiency, which was equal to 0.52% under simulated 100 mW/cm 2 AM 1.5G irradiation, was determined for the device using polyazomethine with three thiophene rings and PC 71 BM created in air with the ITO/PEDOT:PSS (100 cP)/2252Th-DMB:PC 71 BM (1:2)/Al architecture. In addition, the power conversion efficiency was strongly dependent on the viscosity of the PEDOT:PSS used. [ABSTRACT FROM AUTHOR]

The synthesis, optoelectronic, and photovoltaic properties of novel acceptor-donor-acceptor (A-D-A) based π-conjugated functional molecules 1- 3, comprising a planar S,N-heteropentacene as central donor substituted with various terminal acceptor units, such as 1,1-dicyanovinylene (DCV) and 1-(1,1-dicyanomethylene)-cyclohex-2-ene (DCC), are reported. The structural variation of the end groups provides molecules 1- 3 with gradually increased π-conjugation due to a rising number of double bonds, which comes from the DCC unit(s). From optoelectronic investigation, structure-property relationships are deduced and the novel A-D-A heteropentacenes 1- 3 are implemented as photoactive donor component in solution-processed bulk heterojunction solar cells together with [6,6]-phenyl-C61-butyric acid methyl ester as acceptor. The structural variation in the S,N-heteropentacenes leads to clear trends in the photovoltaic performance and power conversion efficiencies of up to 4.9% are achieved. Furthermore, due to extension of the double bonds a clear trade-off between the open circuit voltage ( VOC) and the short circuit current density ( JSC) values is observed. The role of additives on the optimization of the nanoscale morphology and device performance is investigated. The findings presented herein demonstrate that depending on the types of materials the additive may have significantly different effects on the active layer morphology and the device performance. [ABSTRACT FROM AUTHOR]

Two new narrow bandgap D–A conjugated copolymers P1 and P2 containing different fused thiophene donor unit and same benzothiadiazole acceptor unit were synthesized by Stille cross-coupling polymerization, and characterized by 1 H NMR, elemental analysis and GPC, TGA, DSC. Cyclic voltammetry measurement showed that the HOMO energy level both copolymers is deep lying (−5.10 and −5.35 eV for P1 and P2 , respectively) which show that copolymers has good stability in the air and assured a higher open circuit voltage when it photovoltaic application. These copolymer were used as donor along with PC 71 BM and the BHJ polymer solar cells based on P1 :PC 71 BM and P2 :PC 71 BM processed with chloroform (CF) solvent showed over all PCE of 4.54% and 4.36%, respectively. Additionally, the PCE was improved up to 5.62% and 5.24% for P1 :PC 71 BM and P2 :PC 71 BM active layer processed with DIO (4 v%)/CF solvent. The enhancement in the PCE has been attributed to improved nanoscale morphology and crystalline nature of active layer as well as charge transport in the device with the addition of DIO, due to the higher boiling point of DIO causing slow evaporation rate during the film formation. [ABSTRACT FROM AUTHOR]

A series of diketopyrrolopyrrole (DPP)-based conjugated polymers were synthesized with varied side groups such as alkyl and aryl side-chains on a DPP backbone. Their thermal, optical, and photovoltaic properties were investigated. After adding 2% of 1,8-diiodooctane (DIO) as a processing additive in active layers for the bulk heterojunction device, we could achieve the highest PCE of 2.02% with V oc = 0.68 V, J sc = 5.31 mA cm −2 , and FF = 56.0% for PDPPT-s1 :[70]PCBM (1:2). The device for PDPPT-as designed with asymmetrical side groups on the DPP units also showed good solar cell performance comparable with PDPPT-s1 . These results suggest that the DIO additives can control side-chain interference on DPP units. [ABSTRACT FROM AUTHOR]

Two benzothiazole (BT) based donor–acceptor–π–acceptor (D–A–π–A) molecular system denoted as BT3 and BT4 have been designed, synthesized and their optical and electrochemical properties were investigated. The BT4 show wider absorption profile and lower bandgap as compared to BT3 due to the strong electron withdrawing ability of dicyanoquinodimethane (DCNQ) as compared to tetracyanobutadiene (TCBD). The solution processed bulk heterojunction solar cells were fabricated using BT3 and BT4 as electron donor and PC 71 BM as electron acceptor. The organic solar cells optimized dichloromethane (DCM) processed BT3 :PC 71 BM (1:1) and BT4 :PC 71 BM (1:1) showed PCE of 2.56% and 3.68%, respectively. The higher PCE of BT4 :PC 71 BM is related to the wider absorption of the blend and better ordered domain sizes in the blend as compared to BT3 :PC 71 BM. The devices processed with 1,8-diiodoctane (DIO) additives showed PCE of 3.77% and 5.27%, for BT3 :PC 71 BM and BT4 :PC 71 BM blends, respectively. [ABSTRACT FROM AUTHOR]

A polyazomethine (PPV-PAZ-DMB) containing vinylene and aliphatic side chains was synthesized by polycondensation method. The structure of polymer was characterized by means Fourier transform infrared (ATR-FTIR), proton and carbon nuclear magnetic resonance ( 1 H, 13 C NMR) spectroscopy and the results show an agreement with the proposed structure. Photovoltaic properties of PPV-PAZ-DMB were studied by constructing bulk heterojunction (BHJ) solar cells with the architecture ITO/PEDOT:PSS/PPV-PAZ-DMB:PCBM/Al, where ITO: indium tin oxide, PEDOT:PSS: poly(3,4-ethylenedioxythiophene):poly(styrenesulfonate). Photovoltaic parameters were analyzed taking into account amount of [6,6]-phenyl C 61 butyric acid methyl ester ( PCBM) added to PPV-PAZ-DMB and presence of 10-camphorsulfonic acid (CSA) in active layer. With the weight ratio PPV-PAZ-DMB:PCBM of 1:3 and the presence of CSA, the power conversion efficiency (PCE) of the device reached 0.32% with open circuit voltage V oc = 0.47 V, short circuit current density J sc = 2.91 mA/cm 2 and fill factor (FF) 0.25 under simulated 100 mW/cm 2 AM 1.5 G irradiation. It is showed that the PCE of device with CSA was 40 times higher than that of the device without CSA. Devices were additionally tested by electrochemical impedance spectroscopy. An influence of CSA as a dopant on absorption wavelengths, energy gap and HOMO-LUMO levels was investigated. [ABSTRACT FROM AUTHOR]

We report the synthesis and properties of a phthalocyanine derivative with eight fused thienyl rings and eight triisopropylsilylethynyl substituents. The fused thienyl rings were designed to enhance intermolecular interactions among the phthalocyanine molecules in the solid state whereas the triisopropylsilylethynyl substituents were aimed to improve solubility. Compared to the simple octa(2-thienyl) substituted phthalocyanine, a remarkable decrease of solubility and a 67 nm red shift in UV–visible absorption maximum were observed. The fused thienyl compound was used as a donor material in bulk heterojunction solar cells. The power conversion efficiency of 0.60% was achieved under simulated solar illumination. [ABSTRACT FROM AUTHOR]

Two new conjugated D–A polymers P3 (PBTT-d-BTT) and P4 (PBTT-d-TPD) based on same benzo[1,2- b :3,4- b′ :6,5- b ″] trithiophene (BTT) donor and different acceptors monomers 5,8-dibromo-2-dodecanoylbenzo[1,2- b :3,4- b′ :6,5- b ″] trithiophene (d-BTT), and 1,3-dibromo-5-(2-ethylhexyl)thieno[3,4]pyrrol-4,6-dione (d-TPD) respectively, were synthesized by Stille cross-coupling reaction and characterized by gel permeation chromatography (GPC), 1 H NMR, UV–Vis absorption, thermal analysis and electrochemical cyclic voltammetry (CV) tests. Photovoltaic properties of the polymers were studied by using the polymers as donor and PC 71 BM as acceptor with a weight ratio of polymer:PC 71 BM 1:1, 1:2 and 1:2.5. The optimized photovoltaic device was fabricated with an active layer of a blend P3 :PC 71 BM and P4 :PC 71 BM with a blend ratio of 1:2 showed PCE 3.16% and 2.42%, respectively under illumination of AM 1.5 at 100 mW/cm 2 with solar simulator. The PCE of the device based on P3 :PC 71 BM processed with DIO/o-DCB has been further improved up to 4.64% with J sc of 10.52 mA/cm 2 and FF of 0.58 attributed to the increase in crystalline nature of active layer and more balanced charge transport in the device, induced by DIO additive. [ABSTRACT FROM AUTHOR]

A pyrrole-based, imide-functionalized, electron-deficient monomer unit, 4,6-dibromo-2,5-dioctylpyrrolo [3,4-c]pyrrole-1,3(2H,5H)-dione (DPPD), was copolymerized with electron-rich 2,6-bis(trimethyltin)-4,8-bis(2-ethylhexyloxy)benzo[1,2-b:4,5-b']dithiophene to afford the polymer P(BDT-DPPD). The weight-averaged molecular weight (Mw) of P(BDT-DPPD) was 6.41 x 10³ g/mol with a polydispersity index (PDI) of 1.32. P(BDT-DPPD) displayed a broad absorption band from 300 to 600 nm with onset absorption at 596 nm in the film state. The calculated optical bandgap of P(BDT-DPPD) was 2.08 eV, and the estimated highest occupied molecular orbital energy level of P(BDT-DPPD) was -5.48 eV. The polymer solar cell (PSC) fabricated in the ITO/PEDOT:PSS/P(BDT-DPPD)/PC70BM (1:2wt%)/Al configuration was found to give a maximum power conversion efficiency (PCE) of 1.46% with an open-circuit voltage (Voc) of 0.79 V, a current density (Jsc) of 4.59 mA/cm², and a fill factor (FF) of 40%. [ABSTRACT FROM AUTHOR]

A series of two-dimensional (2D) conjugated copolymers with spatial D-A-D structures (PTNBTB, PTCBTB, and PTSBTB) consisting of hetero-atom-bridged dithiophene and phenylvinyl-substituted benzothiadiazole blocks in the main chain have been designed, synthesized, and characterized. The structure-property relationships of the resulting copolymers were systematically investigated. The effects of the bridging atoms (N, C, and Si) on their thermal, optical, electrochemical and charge-transporting properties were also studied. PTNBTB exhibits a smaller band gap with red-shifted absorption, whereas PTSBTB possesses deeper HOMO level and higher hole mobility than PTCBTB or PTSBTB. Bulk heterojunction (BHJ) solar cells were fabricated and characterized with the conventional configuration of ITO/PEDOT:PSS/copolymer:PCBM (1:1)/Ca/Al. As expected, PTSBTB devices showed the highest PCE, up to 4.01%, which was due to the lower HOMO level, higher carrier mobility, and stronger optical response as well as the finer nanoscale phase separation of the pristine polymer and/or the corresponding blending active layer with PCBM. The primary results offer useful insights in designing 2D copolymers with spatial D-A-D backbone and different hetero-atom bridged donor units to finely tune the absorptions, electronic energy levels, carrier mobilities and the photovoltaic properties. [ABSTRACT FROM AUTHOR]