Fabricate Bulk Heterojunction Research Articles

Optimizing Spin-Coat Speed for Fabrication of P3HT: PCBM Solar Cells

The effect of spin speed on the orientation of the conjugated polymer chains becomes a matter of concern while fabricating bulk heterojunction devices such as solar cells. The stability and performance strongly depend on the intertwining of the two molecules that form the bulk heterojunctions. In the case of P3HT: PCBM, it is the long chains of P3HT that encompasses the PCBM molecules. This work investigates the fabricating conditions of Poly (3-hexylthiophene) (P3HT) on the glass substrates in terms of spin coating speeds to obtain favourable geometry of P3HT. For this purpose, three different samples were prepared, keeping spin rate as 6850, 8150 and 9700 rpm, respectively. It was observed that at high spin rates, a large centrifugal force acts upon polymer chains, unfolding them into highly oriented structures. These P3HT chains are free from twists, kinks and are not intermingled. The results of the present work advocate fabricating P3HT: PCBM films at spin speeds less than 6850 rpm.

Comparative Photovoltaics of P3HT:N2200 and P3HT: Small-Gap Fullerene Ethyl-Nipecotate Bulk Heterojunction Structures

This work deals with the study on the optical absorption and photoluminescence spectra of a p-type organic semiconducting polymer, regioregular poly 3-hexylthiophene-2,5-diyl (P3HT) and the absorption spectra of an n-type fullerene-based small-gap fullerene-ethyl nipecotate (Fullerene-EN) and a non-fullerene-based polynaphthalene bithiophene (N2200) semiconducting materials. The band gap of P3HT, N2200, and small-gap fullerene-ethyl nipecotate are 2.42, 1.65, and 1.51 eV, respectively, calculated from experimental results through the Tauc equation. Active layers with blends of P3HT and small-gap fullerene-ethyl nipecotate and P3HT and N2200 have been used to fabricate bulk heterojunction (BHJ) structures. The P3HT:N2200 BHJ structure follows the current density versus voltage characteristics of a photovoltaic device with 0.28% power conversion efficiency, 1.58 mA/cm2 short-circuit current density, and 41% fill factor. However, the P3HT:small-gap fullerene-ethyl nipecotate structure does not show any photovoltaic J–V characteristics.

A New Dibenzoquinoxalineimide-Based Wide-Bandgap Polymer Donor for Polymer Solar Cells.

The molecular design of a wide-bandgap polymer donor is critical to achieve high-performance organic photovoltaic devices. Herein, a new dibenzo-fused quinoxalineimide (BPQI) is successfully synthesized as an electron-deficient building block to construct donor–acceptor (D–A)-type polymers, namely P(BPQI-BDT) and P(BPQI-BDTT), using benzodithiophene and its derivative, which bears different side chains, as the copolymerization units. These two polymers are used as a donor, and the narrow bandgap (2,20-((2Z,20Z)-((12,13-bis(2-ethylhexyl)-3,9-diundecyl-12,13-dihydro-[1,2,5]thiadiazolo [3,4-e]thieno[2,″30′:4′,50]thieno[20,30:4,5]pyrrolo[3,2g]thieno[20,30:4,5]thieno[3,2-b]indole-2,10 diyl)bis(methanylylidene))bis(5,6-difluoro-3-oxo-2,3-dihydro-1H-indene-2,1-diylidene))dimalononitrile) Y6 is used as an acceptor to fabricate bulk heterojunction polymer solar cell devices. Y6, as a non-fullerene receptor (NFA), has excellent electrochemical and optical properties, as well as a high efficiency of over 18%. The device, based on P(BPQI-BDTT):Y6, showed power conversion efficiencies (PCEs) of 6.31% with a JSC of 17.09 mA cm−2, an open-circuit voltage (VOC) of 0.82 V, and an FF of 44.78%. This study demonstrates that dibenzo-fused quinoxalineimide is a promising building block for developing wide-bandgap polymer donors.

Novel Pyrrolo [3,4-b] Dithieno [3, 2-f:2″,3″-h] Quinoxaline-8,10 (9H)-Dione Based Wide Bandgap Conjugated Copolymers for Bulk Heterojunction Polymer Solar Cells.

Two D-A copolymers consisting of fused ring pyrrolo-dithieno-quinoxaline acceptors are synthesized with different donor units, i.e., benzodithiophene (BDT) with alkylthienyl (P134) and 2-ethylhexyloxy (P117) side chains. These copolymers are used as donors and a narrow bandgap acceptor Y6 to fabricate bulk heterojunction polymer solar cell devices. Owing to the strong electron-deficient fused ring pyrrolo-bithieno-quinoxaline and weak alkyl thienyl side chains in BDT, the polymer solar cells (PSCs) based on P134:Y6 attain the power conversion efficiency (PCE) of 15.42%, which is higher than the P117:Y6 counterpart (12.14%). The superior value of PCE for P134:Y6 can be associated with more well-adjusted charge transport, weak charge recombination, proficient exciton generation, and dissociation into free charge carriers and their subsequent charge collection owing to the dense π-π stacking distance and more considerable crystal coherence length for the P134:Y6 thin films. This investigation confirms the great potential of a strong acceptor-weak donor tactic for developing efficient D-A copolymers consists of quinoxaline acceptor for PSCs.

Effect of extending fluorinated thiophene π-bridges of BDT- and TT-based polymers for nonfullerene organic solar cells

A series of novel benzo[1,2-b:4,5-b]dithiophene (BDT) and thieno[3,4-b]thiophene (TT)-based medium-bandgap polymers (PBDTTT-2F and PBDTTT-3F) were synthesized using a Stille cross-coupling reaction; these polymers contain fluorinated thiophene π-bridges. The number-average molecular weights (Mn) of PBDTTT-2F and PBDTTT-3F are 37 kDa and 21 kDa, with dispersities of 2.5 and 2.7, respectively. The bandgap energies of PBDTTT-2F and PBDTTT-3F are 1.75 eV and 1.76 eV, respectively. The absorption regions of PBDTTT-2F and PBDTTT-3F cover 300–700 nm, which is complementary to the absorption range of the nonfullerene acceptor (IT-4F). The polymers were combined with IT-4F to fabricate bulk heterojunction solar cells. The PBDTTT-2F:IT-4F and PBDTTT-3F:IT-4F organic solar cells exhibited power conversion efficiencies (PCEs) of 9.52% and 9.08%, with short-circuit current densities of 17.13 and 16.58 mA cm−2, open-circuit voltages of 0.78 and 0.81 V, and fill factors of 72% and 68%, respectively. The superior PCE of the PBDTTT-2F:IT-4F device compared with that of the PBDTTT-3F:IT-4F device is attributed to the enhanced exciton dissociation, reduced charge recombination, and high carrier mobility in the PBDTTT-2F:IT-4F device.

Lithium‐Doped CuO Nanosheets: Structural Transformation, Optical, and Electrical Characteristics with Enhanced Photocatalytic and Solar Cell Performance

Energy and environmental stuff are two of the main worries for humanity, and nanoscience plays a key role in providing the solution. Huge nano‐research activities have attracted lot of attention in the current scenario. However, designing the material with enhanced optoelectronic properties remains the foremost challenge. In the present work, the Li doped CuO nanosheets are synthesized by the chemical route and examined in photovoltaics and environmental remediation applications. The crystallographic and optical study reveals that crystallite size and bandgap decrease with an increase in lithium‐doping concentration up to 5 mole % and beyond that a reverse trend is observed. Additionally, impedance study has shown the significant contribution of lithium‐ions to the total capacitance and resistivity. Further, the photoactivity of Cu1−xLixO nanosheets (optimum concentration of Cu1−xLixO NSs (x = 0.05)) is projected to the degradation of methylene blue (MB) and used to fabricate bulk heterojunction solar cell together with P3HT and PCBM blend, respectively. The ITO/PEDOT:PSS/P3HT:PC70BM:Cu1−xLixO (x = 0.05)/LiF/Al solar cell realized higher power‐conversion efficiency η ˜ 3.91 than their corresponding pristine device η ˜ 2.98 with enhanced photocurrent density from 9.026 to 11.56 mA cm−2. The proliferation in photocatalysts and solar cells efficiency of Cu1−xLixO (x = 0.05) is mainly attributed to the higher light absorption and lesser electron‐hole recombination. The approach for the synthesis of Cu1−xLixO NSs as potential donor material and device prototypes fabricated is completely safe and cost‐effective.

Comprehensive and Comparative Analysis of Photoinduced Charge Generation, Recombination Kinetics, and Energy Losses in Fullerene and Nonfullerene Acceptor-Based Organic Solar Cells.

In this work, a unique comprehensive and comparative analysis of photoinduced charge generation, recombination kinetics, and energy losses has been carried out to study the effect of different fullerene-based acceptors (FBAs) and nonfullerene acceptors (NFAs) on the performance of organic solar cells (OSCs). For this, different FBAs, specifically ICBA, PC60BM, and PC70BM, and NFAs, namely, ITIC, IT-4F, and IEICO-4F, were employed independently along with a particular donor polymer, PBDB-T, to fabricate bulk heterojunction OSCs and their performances have been compared. This donor molecule is known to give similar power conversion efficiency (PCE) with FBAs and NFAs and hence is ideal for comparative studies. The origin of the higher PCE of NFA-based OSCs vs FBA-based OSCs is analyzed in terms of spectral coverage, charge generation, recombination, and energy loss. It is found that the energy loss (ΔEloss) is ∼0.8 to 1 eV for FBA-based OSCs, while it is 0.5-0.7 eV for NFA-based OSCs. Interestingly, for the PBDB-T:IEICO-4F-based system, energy losses due to charge generation (ΔECT) are ∼0 eV and therefore this system has minimum ΔEloss among all of the studied devices. Providing a systematic, comprehensive, and comparative outlook, our study may further be extended to new upcoming NFA systems and beyond the donor system used in this work.

Fabrication of bulk heterojunction organic solar cells with different configurations using electrospray

In this work, we fabricated bulk heterojunction (BHJ) organic solar cells (OSCs) using electrospray deposition (ESD) with two different device configurations. ITO/PEDOT:PSS/P3HT: PCBM/Ca/Al and ITO/ZnO and TiO2/P3HT: PCBM/MoO3/Ag, termed as direct and inverted OSCs, respectively. In ZnO/ TiO2 -based inverted solar cells, ZnO/ TiO2 films were synthesized by sol-gel process and deposited on ITO deposited glass substrates using the spin-coating technique. P3HT/PCBM blend layers were deposited by using electrospray deposition (ESD). To observe the thermal effects on the device efficiencies, the devices were annealed at different temperatures (up to 140 °C). The cell’s performance parameters were compared at an annealing temperature of 120 °C. Comparing the performance parameters of both types of OSCs at an annealing temperature of 120 °C, the power conversion efficiency (PCE) the 1.62% is found for direct-structured OSC while 1.57% and 1.0% for ZnO/ TiO2-based inverted structures, respectively. Interestingly, the enhanced device performance parameters were obtained with oxides-based OSCs. Compared to ZnO-based inverted OSC, the TiO2-based inverted OSC has lower efficiency which might be due to the highly resistive surface of TiO2 with deep-level traps. These traps can be reduced by light soaking to achieve the optimal power conversion efficiency.

Narrow band gap benzodithiophene and quinoxaline bearing conjugated polymers for organic photovoltaic applications

The reasonable selection and optimization of donor-acceptor units allow the band gap tuning as well as the light absorption ability and the energy levels of the photoactive layer of Bulk Heterojunction (BHJ) solar cells. In this work, a series of new quinoxaline and selenophene based benzo[1,2-b:4,5-b′] dithiophene (BDT) bearing conjugated polymers were synthesized via Pd (0) catalyzed Stille polycondensation reaction. The 2-(2-octyldodecyl)selenophene ring was attached to 4th and 8th positions of phenyl ring in BDT to obtain donor moiety and three different quinoxaline moieties as acceptors were introduced into the BDT backbone. After completion of synthesis of desired polymers, their structures were identified with 1H NMR spectroscopy and their number and weight average molecular weights were examined with gel permeation chromatography (GPC). The effects of introducing fused structure and incorporation of an electron withdrawing F atom to the quinoxaline part on the electrochemical, spectroelectrochemical, optical and morphological properties of the synthesized polymers were examined and correlated to the photovoltaic performance. Both polymers namely P1, P2 and P3 were utilized as donor segments in active layer. They were combined with PC71BM ([6,6]-phenyl C71-butyric acid methyl ester) as the acceptor to fabricate bulk heterojunction solar cells. Highest power conversion efficiencies were found as 2.36% for P1, 2.07% for P2 and 2.45% for P3 under AM 1.5 G (100 mW/cm2) conditions.

Pyrene-benzo[1,2,5]thiadiazole based conjugated polymers for application in BHJ solar cells

Ethylhexyloxy-functionalised pyrene (PEH) was prepared and copolymerised with both dithienyl-benzo[c]-[1,2,5]thiadiazole and dibithiophenyl-benzo[c]-[1,2,5]thiadiazole via a Stille coupling polymerisation method to yield PPEH-DTBT-8 and PPEH-DT2BT-8, respectively. A comparative study was conducted to assess the impact of substituting thiophene for bithiophene repeat units upon the resulting properties of the conjugated polymers. PPEH-DT2BT-8 which has bithiophene spacers between pyrene and benzothiadiazole repeat units, exhibited a narrower optical and electrochemical band gap relative to PPEH-DTBT-8; a consequence of the incorporating bithiophene spacer units which promote intramolecular charge transfer between the electron donating and electron accepting moieties. Both PPEH-DTBT-8 and PPEH-DT2BT-8 showed deep HOMO levels of −5.54 and −5.50 eV, respectively. The polymers possess good thermal stabilities with degradation temperatures in excess of 310 °C. The photovoltaic performance of the two polymers was studied by fabricating bulk heterojunction (BHJ) photovoltaic devices using PC70BM as the acceptor. PPEH-DTBT-8 and PPEH-DT2BT-8 demonstrated efficiencies of 0.33 and 1.83%, respectively. The higher efficiency of PPEH-DT2BT-8 can be attributed to vastly improved FF and Jsc values.

High‐Performance Pseudoplanar Heterojunction Ternary Organic Solar Cells with Nonfullerene Alloyed Acceptor

AbstractThe vast majority of ternary organic solar cells are obtained by simply fabricating bulk heterojunction (BHJ) active layers. Due to the inappropriate distribution of donors and acceptors in the vertical direction, a new method by fabricating pseudoplanar heterojunction (PPHJ) ternary organic solar cells is proposed to better modulate the morphology of active layer. The pseudoplanar heterojunction ternary organic solar cells (P‐ternary) are fabricated by a sequential solution treatment technique, in which the donor and acceptor mixture blends are sequentially spin‐coated. As a consequence, a higher power conversion efficiency (PCE) of 14.2% is achieved with a Voc of 0.79 V, Jsc of 25.6 mA cm−2, and fill factor (FF) of 69.8% compared with the ternary BHJ system of 13.8%. At the same time, the alloyed acceptor is likely formed between two the acceptors through a series of in‐depth explorations. This work suggests that nonfullerene alloyed acceptor may have great potential to realize effective P‐ternary organic solar cells.

Enhanced response of bulk heterojunction polymer photodetectors upon incorporating CsPbBr3 quantum dots

CsPbBr3 quantum dots (QDs) were doped into a blend of poly(3-hexylthiophene) and indene-C60 bisadduct to fabricate bulk heterojunction polymer photodetectors. The addition of the QDs significantly increased the shunt resistance of the device, thereby suppressing the reverse leakage current and improving both the signal-to-noise ratio and the specific detectivity. The photoresponse and recovery time both decreased because of the enhanced built-in electric field and improved charge carrier mobility.

Synthesis and Photovoltaic Properties of A Dithieno[6,5-b:10,11-b′]-8H-Cyclopentyl[1,2-b:4,3-b′]Diphenanthrene based Donor-Acceptor Alternating Copolymer

A novel fused nonacyclic monomer of dithieno[6,5-b:10,11-b′]-8H-cyclopentyl[1,2-b:4,3-b′] diphenanthrene (DTCPDP) was synthesized by combining the structural features of ladder-type and multiple fused multi-cyclic aromatics. DTCPDP has a single sp3-hybridized carbon bridge between fused multi-cyclic aromatics. The copolymerization of DTCPDT with the electron accepting unit of 4,7-di(thiophen-2-yl)benzo[c][1,2,5]thiadiazole (DTBT) via Stille coupling afforded a novel donor-acceptor (D-A) alternating copolymer PDTCPDT-DTBT. The copolymer exhibited good chemical and thermal stabilities, with an optical band gap of 1.82 eV and a low-lying highest occupied molecular orbital (HOMO) energy level of -5.32 eV. When the copolymer was incorporated into polymer: fullerene (PC71BM) blends to fabricate bulk heterojunction polymer solar cell devices, the devices exhibited a moderate maximum power conversion efficiency (PCE) of 5.90%.

Effect of substituents of twisted benzodiperylenediimides on non-fullerene solar cells

Twisted benzodiperylenediimides (TBDPDI) with large rigid conjugated core and strong absorption is regarded as an excellent acceptor in non-fullerene solar cells. Since side chains of semiconductors play a crucial role in the solar cells, TBDPDI acceptors with different side chains (1-ethylpropyl, C5; 2-ethylhexyl, C8; 1-pentylhexyl, C11; 2-octyldodecyl, C20; 1-undecyldodecyl, C23) were synthesized. In solution, TBDPDI compounds (C5, C11, and C23) with alkyl chains branched at 1-position show significantly different absorption profiles and fluorescence intensity with those (C8 and C20) branched at 2-position, due to stronger aggregation of the latter. Nevertheless, alkyl chains have little effect on the molecular orbital energy levels and optical band gaps, as verified by cyclic voltammetry and solid state absorption. Due to their complementary absorption and matchable energy levels with donor of PCE10, these acceptors and PCE10 were used together to fabricate bulk heterojunction (BHJ) solar cells. Because of inferior phase separation with large domain size around 100 nm and bulky insulated side chains, acceptors (C20 and C23) with long alkyl chains have the low electron mobility (μe) around 10−8 cm2 V−1 s−1 and the low power conversion efficiency (PCE) of solar cells. TBDPDI (C11) with 1-pentylhexyl gives the highest PCE of 5.0% under the optimized condition, which is attributed to proper phase separation with domain size around 20 nm and highest μe of 10−6 cm2 V−1 s−1.

Formation of phenyl-C61-butyric acid methyl ester nanoscale aggregates after supercritical carbon dioxide annealing

In this study, we successfully developed a novel method to create [6,6]-phenyl-C61-butyric acid methyl ester (PCBM) nanoscale aggregates using supercritical carbon dioxide (scCO2) annealing and fabricated bulk heterojunction (BHJ) solar cells with the nanoscale PCBM to improve device performance. PCBM forms nanoscale aggregates with a size of approximately 70 nm after scCO2 annealing at 11 MPa and 50 °C for 60 min. However, PCBM remains amorphous after thermal annealing (TA) at 150 °C for 5 min. The morphology, structure, and crystallinity of poly(3-hexylthiophene) (P3HT) in the scCO2-treated P3HT film are nearly the same as those in the TA-treated P3HT film. In the P3HT/PCBM blend, the formation of PCBM nanoscale aggregates by scCO2 treatment decreases the disturbance for P3HT crystallization and improves diffusion and regular packing of P3HT molecular chains. This increases the crystallinity of P3HT so that it becomes higher than that in the TA-treated blend film. The nanoscale aggregates of PCBM and the higher crystallinity of P3HT give the scCO2-treated P3HT/PCBM BHJ solar cells a maximum power conversion efficiency (PCE) of 2.74%, which is much higher than that of the as-cast device (PCE is 1.70%) and a little higher than the highest PCE (2.64%) of thermally annealed devices. These results indicate that scCO2 is an effective, mild, and environmental method to modulate the nanoscale aggregates of PCBM and to improve the PCE of BHJ solar cells. However, the size of the PCBM aggregates is a little larger than the most suitable size of the exciton diffusion length, leading to limited improvement of the PCE.

Double acceptor donor–acceptor alternating conjugated polymers containing cyclopentadithiophene, benzothiadiazole and thienopyrroledione: toward subtractive color organic photovoltaics

Double acceptor copolymers comprising benzothiadiazole (BT), thieno[3,4-c]pyrrole-4,6-dione (TPD) and two cyclopentadithiophene (CPDT) units, and a series of copolymers comprising CPDT-A-CPDT (A: acceptor=BT or TPD) with different numbers of thiophene units have been synthesized by combinations of Suzuki and Stille coupling, direct arylation and oxidative polymerization. Ultraviolet–visible absorption spectra and cyclic voltammograms were measured to compare the optical and electrochemical properties of the polymers. The double acceptor copolymer exhibited hybridized features resulting from the presence of both BT, as well as TPD. On the other hand, an increase in the number of electron donor units resulted in an increase in the band gap for both the TPD and BT series. Organic photovoltaics (OPV) devices were fabricated using the polymers and a fullerene derivative. These donor–acceptor alternating copolymers showed higher OPV performance (power conversion efficiency=3–4%) than other polymers. The active layer comprising the double acceptor polymer and a fullerene derivative showed subtractive color resulting from wide-range visible light absorption, which is advantageous for developing transparent building-integrated OPVs. The OPV performance of BT-based copolymers synthesized via direct arylation was comparable or lower compared with those prepared by conventional cross-coupling polymerizations. Double acceptor donor–acceptor alternating conjugated copolymers comprising thienopyrroledione, benzothiadiazole, two cyclopentadithiophene groups and their analogs with thiophene or bithiophene units have been synthesized by combinations of direct arylation, Suzuki and Stille coupling and oxidative polymerization. These polymers were used to fabricate bulk heterojunction organic photovoltaic (OPV) devices with fullerene derivatives. The active layer comprising the double acceptor polymer with fullerene derivatives showed a subtractive color resulting from wide-range visible light absorption, which is advantageous for practical OPV applications.

Synthesis of pyrrolidinofullerenes and their applications as an n-type component in organic transistors and polymer solar cells

We synthesized pyrrolidinofullerenes functionalized with an electron donor or acceptor group via Prato reaction. Their structures were studied using 1H-NMR, FT-IR and MALDI-TOF mass spectrometry. The electronic energy levels were calculated using quantum chemical calculation based on the density functional theory, showing that the lowest unoccupied molecular orbitals were in the range of −3.7 and −3.9 eV. The electron mobility of one of the fullerene derivatives was as high as 0.05 cm2/(V s), suggesting that pyrrolidinofullerenes can be promising n-type semiconductors. The fullerene derivatives were also blended with P3HT to fabricate bulk heterojunction polymer solar cells, and the performance of solar cells as a function of structural variations of the fullerene derivatives was investigated.

Instigating network structure in bulk heterojunction organic solar cells creating a unique approach in augmenting the optical absorption

In this study, enhancement of device characteristics of poly (3-hexylthiophene): phenyl C61-butyric acid methyl ester (P3HT:PCBM) by changing active layer film morphology into network structure is elucidated. Electrospraying assisted hierarchical assembly of short fibrils provides network structure. Effects of electrospraying parameters such as solvent, polymer blend concentration, applied voltage, tip to collector distance, flow rate and deposition time are analyzed. Solvent and applied voltage is observed to be the major parameters governing the formation of network structure. The optimized conditions are used to investigate the optical and structural properties in the fabricated device. Reflectance studies showed improvement in light absorption due to increased surface area. Structural characterization studies indicate an increase in crystallinity as compared to spincoated samples. The optimized conditions for the electrospun network structures additionally interpenetrated by P3HT:PCBM solution by spin coating are used to fabricate bulk heterojunction device. Device characteristics showed an increase in short circuit current and thus increase in efficiency from 2.18% to 3.66%. There is a enhancement of 37.5% going from a maximum external quantum efficiency of 40%–55% for electrosprayed and spincoated devices. This work suggests that network morphology could be used to enhance the photovoltaic properties.

Porphycene-Diketopyrrolopyrrole Conjugates As p-Type Organic Solar Cell Materials

Porphycene is a constitutional isomer of porphyrin. Porphycene has a lower LUMO level and smaller HOMO-LUMO difference than porphyrin since its molecular symmetry is lower than that of porphyrin. 1 These properties have allowed us to explore the possible applications of porphycenes in the fields of photodynamic therapy (PDT), photoinactivation of viruses and bacteria, protein mimicry, nonlinear optics, and catalysis. Recently, we have focused on the porphycene using as the semiconducting materials for organic solar cell (OSC). OSC materials require for the absorption covering the visible to NIR regions and appropriate HOMO and LUMO energy levels. In this presentation, we have designed, synthesized and properties of the porphycene–diketopyrropyrrole conjugate (Pc–DPP) though ethynyl linkages for the OSC as p-type materials. The absorption of the DPP unit appears at around 450-550 nm, while porphycene has an absorption valley around 400-550 nm. The combination of DPP and porphycene via ethynyl linkages is expected to generate absorption covering the visible to NIR regions of the spectrum. We have measured absorption spectra of Pc–­DPP and 2,7,12,17-tetrahexylporphycene (THPc) as reference compound in thin-film on glass substrate. THPc has strong Soret band at 400 nm and Q-bands around 550 to 700 nm. On the other hand, as the result of the connection with porphycene and DPP units, Pc–DPP has broad absorption covering the visible to near in-fared regions. Based on these optical characters, we have fabricated bulk heterojunction (BHJ) OSC by solution process with Pc–DPP as a p-type material and PC61BM as an n-type material. The active layer of the mixture of Pc–DPP and PC61BM with 0.1% 1,8-diiodooctane containing chloroform was deposited on the PEDOT:PSS-treated ITO substrate by spin coating and then calcium and aluminum electrode were deposited on the active layer by vacuum process. After optimized the device conditions, we achieved the PCEs of 1.4% (J sc = 4.88 mA cm-2, V oc = 0.81 V and FF = 0.37). We will also report the evaluations of film structures of these devices by AFM and XRD measurements.

Copper nanowire-graphene core-shell nanostructure for highly stable transparent conducting electrodes.

A copper nanowire-graphene (CuNW-G) core-shell nanostructure was successfully synthesized using a low-temperature plasma-enhanced chemical vapor deposition process at temperatures as low as 400 °C for the first time. The CuNW-G core-shell nanostructure was systematically characterized by scanning electron microscopy, transmission electron microscopy, X-ray diffraction, Raman, and X-ray photoelectron spectroscopy measurements. A transparent conducting electrode (TCE) based on the CuNW-G core-shell nanostructure exhibited excellent optical and electrical properties compared to a conventional indium tin oxide TCE. Moreover, it showed remarkable thermal oxidation and chemical stability because of the tight encapsulation of the CuNW with gas-impermeable graphene shells. The potential suitability of CuNW-G TCE was demonstrated by fabricating bulk heterojunction polymer solar cells. We anticipate that the CuNW-G core-shell nanostructure can be used as an alternative to conventional TCE materials for emerging optoelectronic devices such as flexible solar cells, displays, and touch panels.