梅山 有和

Neat ITIC films are found to facilitate charge transfer, dissociation, and free carrier formation without the need for donor layers. This process, driven by V-type molecular stacking, significantly boosts organic photovoltaic efficiency.

An unusual emissive charge-transfer excited state was formed at the pyrene–MoS₂ interface.

Interfacial electron transfer across perovskite-electron acceptor heterojunctions plays a significant role in the power-conversion efficiency of perovskite solar cells. Thus, electron donor-acceptor thin films of halide perovskite nanocrystals receive considerable attention. Nevertheless, understanding and optimizing distance- and thickness-dependent electron transfer in perovskite-electron acceptor heterojunctions are important. We reveal the distance-dependent and diffusion-controlled interfacial electron transfer across donor-acceptor heterojunction films formed by formamidinium or cesium lead bromide (FAPbBr3/CsPbBr3) perovskite nanocrystals with TiO2/C60. Self-assembled nanocrystal films prepared from FAPbBr3 show a longer photoluminescence lifetime than a solution, showing a long-range carrier migration. The acceptors quench the photoluminescence intensity but not the lifetime in a solution, revealing a static electron transfer. Conversely, the electron transfer in the films changes from dynamic to static by moving toward the donor-acceptor interface. While radiative recombination dominates the electron transfer at 800 μm or farther, the acceptors scavenge the photogenerated carriers within 100 μm. This research highlights the significance of interfacial electron transfer in perovskite films.

A comprehensive study on the relationship between the structure and the photophysical and photovoltaic properties of acceptor-donor-acceptor (A-D-A) type nonfullerene acceptors (NFAs) is of pivotal importance to obtain design guidelines for high-performance organic photovoltaics (OPVs). In this study, we synthesized a D unit, NTT, in which the central benzene core, indacenodithieno[3,2-b]thiophene (IT), is replaced by naphthalene. Notably, NTTIC, an A-D-A type NFA with NTT as the D unit, showed a longer singlet exciton lifetime in the film than the IT-based benchmark NFA, ITIC. When paired with a conjugated polymer donor, PBDB-T, the NTTIC-based OPV device exhibited a higher power conversion efficiency (PCE = 9.95%) than the ITIC-based device (9.71%). Furthermore, due to the larger domain size of NTTIC in PBDB-T:NTTIC, the exciton diffusion (ED) at the donor/acceptor interface and the charge transfer (CT) were slower (14 ps in total) than those of PBDB-T:ITIC (7 ps in total). Nevertheless, the total efficiency of the ED and CT in PBDB-T:NTTIC was similar to that in PBDB-T:ITIC (95%) owing to the longer singlet exciton lifetime of the NTTIC film. These results demonstrate the high potential of naphthalene-cored D units of A-D-A type NFAs to achieve a long singlet exciton lifetime and a resultant high PCE in NFA-based OPVs.

Scalable and transparent polyether-based waterborne polyurethane (WPU) thin films that adhere firmly to Al nanofilm but not to PET film without release agents have been designed and prepared. In order to realize cleaner production, eco-friendly acetyl tributyl citrate (ATBC) instead of toxic additives like N-methylpyrrolidone was introduced into polymerization system as both an effective dispersant of dimethylolpropionic acid crystal as hydrophilic chain extender and a viscosity thinner of the synthesized precursors to promote homogeneous hydrophilic extension reaction in the absence of toxic catalysts. The appropriate ATBC and dimethylolpropionic acid contents are critical to formation of stable translucent dispersion of the WPU with total hard segments as high as 56 wt% at –NCO/-OH molar ratio of 1.05. Molecular structure and ATBC existence of the WPU film have been characterized by IR, NMR, gas chromatography, and thermogravimetry, suggesting that ATBC will not release into the environment even if at 140 °C because of its high boiling point and ultralow volatility. The reserved ATBC in the WPU film also acts as an effective plasticizer and lubricant so that the WPU film can be quickly peeled off from PET. The lowest T-peel strength of 1.3 N m−1 on PET is achieved for the WPU film with a high tensile strength of 15.8 MPa and a medium elongation at break of 237%. The WPU films have tunable stickiness onto PET film from sticky to completely nonsticky. Importantly, the WPU films offer simultaneously strong adhesion to Al nanofilm and high thermal stability but high peelability from the PET, allowing to fabricate a stable holographic/photolithographic composite film by Al deposition at &gt 1000 °C and ensure high flatness and luster of the composite film. Optimal formulations of WPU materials with high comprehensive performance including good film-processability, ultralow VOC emission, high mechanical and thermal properties, controllable surface tension, and tunable adhesion to Al nanofilm have been proposed for transferable holographic films.

Morphological control of C60 fullerene using liquefied porphyrins (1 and 2) as the host matrices was explored. Slow evaporation of the solvent of the equimolar mixture of porphyrin and C60 in toluene afforded the porphyrin/C60 composite with a 3:1 molar ratio. The stoichiometric binding behaviors suggest that specific porphyrin-C60 interactions operate the formation of the porphyrin/C60 composites, as corroborated by spectroscopic and thermal properties, and glazing-incidence wide-angle X-ray diffraction. Under the bulk conditions, the conventional thermodynamic advantage of multiple binding cooperativity for molecular recognition is unlikely to explain the stoichiometric binding behaviors. Instead, we propose a size-matching effect on the porphyrin-C60 interaction in the bulk porphyrin matrices, i.e., "supramolecular solvation". The glassy nature of the porphyrin matrices was transmitted to C60 through the specific interaction, and the porphyrin/C60 composites adopted glassy states at room temperature.

Phase-separated structures in photoactive layers composed of electron donors and acceptors in organic photovoltaics (OPVs) generally exert a profound impact on the device performance. In this study, nonfullerene acceptors (NFAs) where a heteronanographene central core was furnished with branched alkoxy chains of different lengths, TACIC-EH, TACIC-BO, and TACIC-HD, were prepared to adjust the aggregation tendency and systematically probe the relationships of film structures with photophysical and photovoltaic properties. The side-chain length showed negligible effects on the absorption properties and energy levels of TACICs. In addition, regardless of the chain length, all TACIC films exhibited characteristically long singlet exciton lifetimes (1330-2330 ps) compared to those in solution (≤220 ps). Using a conjugated polymer donor, PBDB-T, the best OPV performance was achieved with TACIC-BO that contained medium-length chains, exhibiting a power conversion efficiency (PCE) of 9.92%. TACIC-HD with the longest chains showed deteriorated electron mobility due to the long insulating alkoxy groups. Therefore, the PBDB-T:TACIC-HD-based device revealed a low charge collection efficiency and PCE (8.21%) relative to the PBDB-T:TACIC-BO-based device, but their film morphologies were analogous. Meanwhile, TACIC-EH with the shortest chains showed low solubility and formed micrometer-sized large aggregates in the blend film with PBDB-T. Although the charge collection efficiency of PBDB-T:TACIC-EH was lower than that of PBDB-T:TACIC-BO, the efficiencies of exciton diffusion to the donor-acceptor interface were sufficiently high (>98%) owing to the elongated singlet exciton lifetime of TACIC-EH. The PCE of the PBDB-T:TACIC-EH-based device remained moderate (7.10%). Therefore, TACICs with the long singlet exciton lifetimes in the films provide a clear guideline for NFAs with low sensitivity of OPV device performance to the blend film structures, which is advantageous for large-scale OPV production with high reproducibility.

Carbon nanotubes (CNTs) interlocked by cyclic compounds through supramolecular interaction are promising rotaxane-like materials applicable as 2D and 3D networks of nanowires and disease-specific theranostic agents having multifunctionalities. Supramolecular complexation of CNTs with cyclic compounds in a “ring toss'' manner is a straightforward method to prepare interlocked CNTs however, to date, this has not been reported on. Here, the “ring toss” method to prepare interlocked CNTs by using π-conjugated carbon nanorings: [8]-, [9]-, and [10]cycloparaphenyleneacetylene (CPPA) is reported. CPPAs efficiently interact with CNTs to form CNT@CPPA complexes, while uncomplexed CPPAs can be recovered without decomposition. CNTs, which tightly fit in the cavities of CPPAs through convex–concave interaction, efficiently afford “tube-in-ring”-type CNT@CPPA complexes. “Tube-in-ring”-type and “ring-on-tube”-type complexation modes are successfully distinguished by spectroscopic, thermogravimetric, and microscopic analyses.

Small-sized single crystalline silicon solar cells (ca. 25 mm2) were fabricated by a non-vacuum process as an energy supply for small devices (ubiquitous devices: a wristwatch, desktop calculator etc.) and processed for a tandem solar-cell research. A side-edge etching procedure was performed in order to eliminate detrimental cracks to improve photovoltaic properties. Moreover, the new structure of the small-sized solar cell with side contact provides reduced shadow loss of contacts. After the structural and procedural optimization, a conversion efficiency of 16.4% was achieved by a non-vacuum process with 3 mm × 8 mm surface dimension solar cell. Finally, the photovoltaic characteristics of small silicon cells, as a function of light intensity for the ubiquitous purposes were compared with amorphous silicon solar cells. In addition, the facile processed silicon solar cell was integrated into mechanically-stacked tandem solar cells with perovskite solar cells by direct contact of TCO layers of each sub-cell. The counter electrode MoOX/IZO over HTM (spiro-OMeTAD) in top perovskite cells is physically placed on top of the bottom Si solar cell to form a series tandem configuration.

Composite films that consisted of C60 and well-exfoliated nanosheets of transition metal dichalcogenides (TMDs), such as MoS2 or WS2, with a bulk heterojunction structure were easily fabricated onto a semiconducting SnO2 electrode via a two-step methodology: self-assembly into their composite aggregates by injection of a poor solvent into a good solvent with the dispersion, and subsequent electrophoretic deposition. Upon photoexcitation, the composites on SnO2 exhibited enhanced transient conductivity in comparison with single components of TMDs or C60, which demonstrates that the bulk heterojunction nanostructure of TMD and C60 promoted the charge separation (CS). In addition, the decoration of the TMD nanosheets with C60 hindered the undesirable charge recombination (CR) between an electron in SnO2 and a hole in the TMD nanosheets. Owing to the accelerated CS and suppressed CR, photoelectrochemical devices based on the MoS2–C60 and WS2–C60 composites achieved remarkably improved incident photon-to-current efficiencies (IPCEs) as compared with the single-component films. Despite more suppressed CR in WS2–C60 than MoS2–C60, the IPCE value of the device with WS2–C60 was smaller than that with MoS2–C60 owing to its inhomogeneous film structure.

The effects of regioisomer and diastereomer separations of [70]PCBM on structures and photovoltaic properties of PffBT4T-2OD:[70]PCBM blend films have systematically been investigated for the first time. Decreasing the amount of a diastereomer of β-[70]PCBM with high aggregation tendency (β1-[70]PCBM) improved the photovoltaic performances.

Isomer-controlled [70]fullerene bis-adducts can achieve high performance as electron-acceptors in organic photovoltaics (OPVs) because of their stronger absorption intensities than [60]fullerene derivatives, higher LUMO energy levels than mono-adducts, and less structural and energetic disorder than random isomer mixtures. Especially, attractive are cis-1 isomers that have the closest proximity of addends owing to their plausible more regular close packed structure. In this study, propylene-tethered cis-1 bismethano[70]fullerene with two methyl, ethyl, phenyl, or thienyl groups were rationally designed and prepared for the first time to investigate the OPV performances with an amorphous conjugated polymer donor (PCDTBT). The cis-1 products were found to be a mixture of two regioisomers, α-1-α and α-1-β as major and minor components, respectively. Among them, the cis-1 product with two ethyl groups (Et2-cis-1-[70]PBC) showed the highest OPV performance, encouraging us to isolate its α-1-α isomer (Et2-α-1-α-[70]PBC) by high-performance liquid chromatography. OPV devices based on Et2-cis-1-[70]PBC and Et2-α-1-α-[70]PBC with PCDTBT showed open-circuit voltages of 0.844 V and 0.864 V, respectively, which were higher than that of a device with typical [70]fullerene mono-adduct, [70]PCBM (0.831 V) with a lower LUMO level. However, the short-circuit current densities and resultant power conversion efficiencies of the devices with Et2-cis-1-[70]PBC (9.24 mA cm-2, 4.60%) and Et2-α-1-α-[70]PBC (6.35 mA cm-2, 3.25%) were lower than those of the device with [70]PCBM (10.8 mA cm-2, 5.8%) due to their inferior charge collection efficiencies. The results obtained here reveal that cis-1 [70]fullerene bis-adducts do not guarantee better OPV performance and that further optimization of the substituent structures is necessary.

Over the past several years, organometal halide perovskite solar cells (PSCs) have attracted considerable interest from the scientific research community because of their potential as promising photovoltaic devices for use in renewable energy production. To date, high power conversion efficiencies (PCEs) of more than 20% have been primarily achieved with mesoscopic-structured PSCs, where a mesoporous TiO2 (mTiO(2)) layer is incorporated as an electron-transporting mesoporous scaffold into the perovskite crystal, in addition to a compact TiO2 (cTiO(2)) as an electron-transporting layer (ETL). In this Perspective, we first summarize recent research on the preparation strategies of the mTiO(2) layer with a high electron transport capability by facile sol-gel methods instead of the conventional nanoparticle approach. The importance of the control of the pore size and grain boundaries of the mTiO(2) in achieving high PCEs for PSCs is discussed. In addition, an alternative method to improve the electron transport in the mTiO(2) layer via the incorporation of highly conductive nanocarbon materials, such as two-dimensional (2D) graphene and one-dimensional (1D) carbon nanotubes, is also summarized. Finally, we highlight the utilization of zero-dimensional (0D) nanocarbon, i.e., fullerenes, as an n-type semiconducting material in mesostructure-free planar PSCs, which avoids high-temperature sintering during the fabrication of an ETL.

Liquid crystalline donor (i.e., phthalocyanine) was covalently linked to acceptor (i.e, fullerene) to achieve efficient charge-transport properties in a liquid crystalline phase. The columnar structure exhibited highly efficient ambipolar charge-transport character, demonstrating the potential utility of the strategy in organic electronics. © 2011 American Chemical Society.

We report herein unprecedented long-range observation of both formation and decay of the exciplex state in donor (D)-bridge (B)-acceptor (A) linked systems. Zinc porphyrins (ZnP) as a donor were tethered to single-walled carbon nanotube (SWNT) as an acceptor through oligo(p-phenylene)s (ZnP-ph(n)-SWNT) or oligo(p-xylene)s (ZnP-xy(n-1)-ph(1)-SWNT) with systematically varied lengths (n = 1-15) to address the issue. Exponential dependencies of rate constants for the exciplex formation (k(FEx)) and decay (k(DEx)) on the edge-to-edge separation distance between ZnP and SWNT through the bridges were unambiguously derived from time resolved spectroscopies. Distance dependencies (i.e., attenuation factor, beta) of k(FEx) and k(DEx) in ZnP-ph(n)-SWNT were found to be considerably small (beta = 0.10 for k(FEx) and 0.12 angstrom(-1) for kDEx) compared to those for charge separation and recombination (0.2-0.8 angstrom(-1)) in D-B-A systems with the same oligo(p-phenylene) bridges. The small beta values may be associated with the exciplex state with mixed characters of charge-transfer and excited states. In parallel, the substantially nonconjugated bridge of oligo(p-xylene)s exhibited larger attenuation values (beta = 0.12 for k(FEx) and 0.14 angstrom(-1) for k(DEx)). These results provide deep insight into the unique photodynamics of electronically strongly coupled D-B-A systems involving exciplex.

Despite numerous organic semiconductors being developed during the past decade, C-70 derivatives are predominantly used as electron acceptors in efficient polymer solar cells (PSCs). However, as-prepared C-70 mono-adducts intrinsically comprise regioisomers that would mask individual device performances depending on the substituent position on C-70. Herein, we separate the regioisomers of C-70 monoadducts for PSC applications for the first time. Systematic investigations of the substituent position effect using a novel symmetric C-70 mono-adduct ([70] NCMA) and a prevalent, high-performance one ([70] PCBM) reveals that we can control the structures of the blend films with conjugated polymers and thereby improve the PSC performances by regioisomer separation. Our approach demonstrates the significance of exploring the best-matching regioisomer of C-70 mono-adducts with high-performance conjugated polymers, which would achieve a remarkable progress in PSC devices.

In perovskite solar cells (PSCs), electron selective layers (ESLs) assume a crucial role in blocking holes and transporting electrons for high performances. To achieve low-temperature solution processing of PSCs, organic n-type materials such as fullerene-based molecules have recently been employed to replace a typical TiO2 ESL that requires high temperature (>450 degrees C) for fabrication. Herein, soluble C-60-9-methylanthracene mono-adduct (C-60(9MA)) is used as a thermal precursor to the C-60 ESL in planar PSCs. The best performing PSC device shows a power conversion efficiency of 15.0% under the simulated AM 1.5G one sun illumination, which is superior to that of the device with compact TiO2 as an ESL (12.9%). Remarkably, a fill factor of the C-60-based PSC (0.723) is enhanced compared to that of the TiO2-based one (0.671) owing to the low charge-transfer resistance at the interface of C-60-perovskite. These results suggest that the thermal precursor approach to pristine fullerene films is a promising approach for fabricating ESL in high-performance PSCs with relatively low fabrication temperature (<140 degrees C). (C) The Author(s) 2017. Published by ECS.

Despite the wide prevalence of [6,6]-phenyl-C-71-butyric acid methyl ester ([70] PCBM) as an electron acceptor in high-performance organic photovoltaic (OPV) devices, [70] PCBM has been generally used as a mixture of regioisomers. In this study, we utilized regioisomerically pure alpha- and beta-[70] PCBM in combination with a crystalline conjugated polymer donor, poly(3-hexylthiophene) (P3HT) to investigate systematically the regioisomer effects of [70] PCBM on structures and electronic and photovoltaic properties of the composite films. Notably, the beta-isomer induced a face-on P3HT packing in the blend film, whereas an edge-on alignment of P3HT was observed in the composite films with the alpha-isomer as well as the regioisomer mixture (mix-[70] PCBM). The hole mobility in a vertical direction to the substrate in the P3HT: beta-[70] PCBM film was higher than those in P3HT: alpha-[70] PCBM and P3HT: mix-[70] PCBM due to the face-on P3HT packing. Reflecting the superior hole mobility, the OPV device based on the P3HT: beta-[70] PCBM film showed a higher power conversion efficiency of 3.69% than the devices based on the other composite films (3.11-3.21%). The results obtained here demonstrate that the use of regioisomerically pure [70] fullerene mono-adducts can modulate the polymer packing direction in the blend film, which is an unprecedented approach to improve the device performances of OPVs.

The photoexcitation of the pyrene dimer on graphene resulted in the final formation of a charge-separated state following an exciplex formation, while that of the pyrene monomer on graphene generated the corresponding exciplex solely due to the difference in the electronic coupling between the pyrene and the graphene.

Porphyrin dimers were covalently grafted onto electron-accepting single-walled carbon nanotube (SWNT) sidewalls by direct aryl radical addition reaction with an m-or p-phenylene linker with the help of p-p interaction between the porphyrins. A splitting of the porphyrin Soret band and DFT calculations supported the selective formation of the porphyrin dimers on the sidewall of SWNTs. Photoexcitation of the porphyrin dimers on the SWNT resulted in the formation of the exciplex state, which directly decayed to the ground state without yielding the complete charge-separated state. Lifetimes of the porphyrin dimer-SWNT exciplex were longer than that of a porphyrin monomer-SWNT exciplex due to the stabilization by p-electron interaction over two porphyrin rings. In addition, the weaker electronic coupling through the meta-linkage than the para-one may be responsible for the exciplex lifetime of the porphyrin dimer-SWNT with the m-phenylene linker (49 ps) longer than that with the p-phenylene one (24 ps). The results obtained here provide the basic information on the effect of the donor dimerization on the photodynamic behavior of the exciplex state in donor-acceptor linked systems. [Figure presented]

Research of CH3NH3PbI3 perovskite solar cells had significant attention as the candidate of new future energy. Due to the toxicity, however, lead (Pb) free photon harvesting layer should be discovered to replace the present CH3NH3PbI3 perovskite. In place of lead, we have tried antimony (Sb) and bismuth (Bi) with organic and metal monovalent cations (CH3NH3+, Ag+ and Cu+). Therefore, in this work, lead-free photo-absorber layers of (CH3NH3)3Bi2I9, (CH3NH3)3Sb2I9, (CH3NH3)3SbBiI9, Ag3BiI6, Ag3BiI3(SCN)3 and Cu3BiI6 were processed by solution deposition way to be solar cells. About the structure of solar cells, we have compared the normal (n-i-p: TiO2-perovskite-spiro OMeTAD) and inverted (p-i-n: NiO-perovskite-PCBM) structures. The normal (n-i-p)-structured solar cells performed better conversion efficiencies, basically. But, these environmental friendly photon absorber layers showed the uneven surface morphology with a particular grow pattern depend on the substrate (TiO2 or NiO). We have considered that the unevenness of surface morphology can deteriorate the photovoltaic performance and can hinder future prospect of these lead-free photon harvesting layers. However, we found new interesting finding about the progress of devices by the interface of NiO/Sb3+ and TiO2/Cu3BiI6, which should be addressed in the future study.

Engineering of photonics for antireflection and electronics for extraction of the hole using 2.5 nm of a thin Au layer have been performed for two- and four-terminal tandem solar cells using CH3NH3PbI3 perovskite (top cell) and p-type single crystal silicon (c-Si) (bottom cell) by mechanically stacking. Highly transparent connection multilayers of evaporated-Au and sputtered-ITO films were fabricated at the interface to be a point-contact tunneling junction between the rough perovskite and flat silicon solar cells. The mechanically stacked tandem solar cell with an optimized tunneling junction structure was (perovskite for the top cell/Au (2.S nm)/ITO (154 nm) stacked-on ITO (108 nm)/c-Si for the bottom cell). It was confirmed the best efficiency of 13.7% and 14.4% as two and four-terminal devices, respectively.

A series of chemically converted graphenes (CCGs) covalently functionalized with multiple zincporphyrins (ZnPs) through tuned lengths of linear oligo-p-phenylene bridges (ZnP-ph(n)-CCG, n = 1-5) were prepared to address the bridge length effect on their photodynamics. Irrespective of the bridge length, photoexcitation of ZnP-ph(n)-CCG led to exclusive formation of an exciplex state, which rapidly decayed to the ground state without yielding the completely charge-separated state. The notable dependence of the exciplex lifetime as a function of separation distance between the porphyrin and CCG has been observed for the first time, supporting the hypothesis that the decay to the ground state is dominated by the through-space interaction rather than the through-bond one. The basic information on the interaction between ZnP and CCG in the excited state will provide us with deeper insight on the intrinsic nature of the exciplex state as a function of donor-acceptor interaction.

Tin-doped indium oxide (ITO) sputtering is known as a damaging cause on organic hole transporting material in solar cells. In order to gain more insights into the reasons for poor device performance of perovskite solar cells by the ITO sputtering on Spiro-OMeTAD, here we present an in-depth study by I-V simulation analysis using corresponding equivalent circuit models. First, experimental I-V data were obtained for the perovskite solar cells with (FTO/TiO2(dense)/TiO2(mesoporous)/CH3NH3PbI3/Spiro-OMeTAD/ITO/Au) configuration. An Au layer (t = SO nm) was deposited on the ITO as a contact layer. The simulation studies indicated that sputtering of ITO onto Spiro-OMeTAD introduced a reverse Schottky diode and an additional diode to the device that could be relating the sputtering damage of the Spiro-OMeTAD layer. By considering the parameter of the reverse diode element as a function of sputtering time, it was found that the barrier height of the reverse Schottky diode was enhanced by the sputtering damage against Spiro-OMeTAD, which could be the key reason for the reduced fill factor of the devices.

To shed a light on fundamental molecular functions of photoinduced charge conductions by organic photovoltaic materials, it is important to directly observe molecular geometries of the intermediate charges just after the photoinduced electron-transfer reactions. However, highly inhomogeneous molecular environments at the bulk heteojunction interfaces in the photoactive layers have prevented us from understanding the mechanism of the charge conductions. We have herein investigated orbital geometries, electronic couplings, and hole-dissociation dynamics of photo induced charge-separated (CS) states in a series of poly(3-hexylthiophene) fullerene linked dyads bridged by rigid oligo-p-phenylene spacers by using time-resolved EPR spectroscopy. It has been revealed that one-dimensional intramolecular hole-dissociations exothermically take place from localized holes in initial CS states, following bridge-mediated, photoinduced charge separations via triplet exciton diffusions in the conjugated polymer-backbones. This molecular wire property of the photoinduced charges in solution at room temperature demonstrates the potential utility of the covalently bridged polymer molecules applied for the molecular devices.

The photovoltaic performance of a perovskite solar cell based on a new electron conducting SnO2 film prepared at low temperature using different solvents was investigated. SnO2 was selected as an electron conducting medium due to its superior properties over TiO2, such as better antireflective properties, higher electron mobility, more suitable band edges and a wider band gap. A SnO2 layer was developed by spin-coating SnCl2 solution followed by annealing at 200 degrees C in air. The low-temperature (200 degrees C) annealed SnO2 layer exhibits enhanced crystallization, high transmittance, and uniform surface morphology using ethanol as a solvent rather than water. Solid state CuSCN hole conductor was used as HTM for reducing the device cost. A planar solar cell fabricated with CH3NH3PbI3 perovskite infiltrated SnO2 showed a power conversion efficiency of 8.38% with short-circuit current density of 18.99 mA cm(-2), an open-circuit voltage of 0.96 mV and a fill factor of 45%. The devices were fabricated at >60% humidity level at room temperature. The results suggest that SnO2 is an effective charge collection system for CH3NH3PbI3 based planar perovskite solar cells. In addition, these results provide a new direction for the future improvement of perovskite solar cells using new electron conducting layers. (C) 2016 Elsevier B.V. All rights reserved.

A thermal precursor approach can serve as a solution-based process to form high-quality organic thin-films from small molecules with low solubility such as pristine fullerenes. In this study, highly-soluble C-60-9-methylanthracene (9MA) adducts, of which the appended 9MA groups can be easily detached and evaporated by heating, were used as thermal precursors to C-60. In a composite film of C-60-9MA adducts with an amorphous polymer, poly(2,7-carbazole-alt-dithienylbenzothiadiazole) (PCDTBT) for bulk heterojunction (BHJ) solar cells, the C-60 aggregation was suppressed even after the thermal detachment of the 9MA groups at high temperature up to 160 degrees C. This result is contrasted with a composite film of the C-60-9MA adducts and a crystalline conjugated polymer, poly(3-hexylthiophene) (P3HT), yielding undesirable large aggregates by thermal annealing. The organic photovoltaic (OPV) device based on the composite film of the C-60-9MA adducts and PCDTBT showed a low power conversion efficiency (PCE) of 0.69%, which was remarkably improved up to 3.51% by a factor of ca. 5 after the thermal annealing treatment. Importantly, the maximum PCE was achieved at 140 degrees C, where an increase of the short-circuit current density (J(SC)) and a decrease of the open-circuit voltage (V-OC) are well-balanced with increasing the annealing temperature. The results obtained here demonstrate the potential utility of the unique thermal precursor approach to form high-quality BHJ films from amorphous conjugated polymers and highly-insoluble fullerenes, expecting higher LUMO levels and V-OC for applications in organic thin-film OPV devices made by cost-effective solution-based processes.

Using X-ray diffraction (XRD), it was confirmed that the deposition of hole-transporting materials (HTM) on a CH3NH3PbI3 perovskite layer changed the CH3NH3PbI3 perovskite crystal, which was due to the material exchanging phenomena between the CH3NH3PbI3 perovskite and HTM layers. The solvent for HTM also changed the perovskite crystal. In order to suppress the crystal change, doping by chloride ion, bromide ion and 5-aminovaleric acid was attempted. However, the doping was unable to stabilize the perovskite crystal against HTM deposition. It can be concluded that the CH3NH3PbI3 perovskite crystal is too soft and flexible to stabilize against HTM deposition.

A general polymer, poly(methyl methacrylate) (PMMA) is utilized as a unique templating agent for forming crack-free mesoporous TiO2 films by a sol-gel method. The pore morphologies were found to be controllable by varying the amount of PMMA. The PMMA-mediated mesoporous TiO2 layer has been applied for the first time to perovskite solar cells exhibiting a best power conversion efficiency of >= 14%, which is ca. three times higher than that using a TiO2 layer prepared by the same sol-gel method without the polymer addition (5.28%). Remarkably, it was superior to the reference device with mesoporous TiO2 layer prepared with conventional nanopartide paste (13.1%). Such mesostructure-tuned TiO2 layers made by the facile sol-gel technique with a commercially available polymer additive has the great potential to contribute significantly toward the development of low-cost, highly efficient perovskite solar cells as well as other functional hybrid devices.

The effects of the inclusion of reduced graphene oxide (RGO) in TiO2 layers on performance of perovskite solar cells were systematically investigated. For this purpose, a wet chemical approach was examined to embed graphene oxide (GO) across the thickness of compact TiO2 (cTiO(2)) and mesoporous TiO2 (mTiO(2)) layers, which was followed by a thermally driven in situ conversion from GO to RGO. The presence of RGO at loadings of 0.15 wt % in the cTiO(2) layer and of 0.015 wt % in the mTiO(2) layer led to a power conversion efficiency (PCE) from 6.6% to 9.3% by 40% increase.

We have prepared perovskite [CH3NH3PbI3 (MALI), CH3NH3PbBr3 (MALB), NH2CH=NH2PbI3 (FALI), and NH2CH=NH2PbBr3 (FALB)] thin films by a one-step process on glass/TiO2 and glass/Al2O3 substrates and studied the stability of the perovskite under UV/visible light radiation up to 24 h at 1.5AM in air. After irradiation, the films were characterized by UV-vis absorption and X-ray diffraction measurements. In addition, photovoltaic performance characteristics in air were studied using different perovskites before (0 h) and after 24 h irradiation. The results revealed that Al2O3 protected the perovskite crystal from degradation. However, the perovskites were unstable except for NH2CH=NH2PbI3 un der the same conditions using a TiO2 scaffold layer. (C) 2015 The Japan Society of Applied Physics

The close solid-state structure-property relationships of organic pi - aromatic molecules have attracted interest due to their implications for the design of organic functional materials. In particular, a dimeric structure, that is, a unit consisting of two molecules, is required for precisely evaluating intermolecular interactions. Here, we show that the sidewall of a singlewalled carbon nanotube (SWNT) represents a unique molecular dimer platform that can be directly visualized using high-resolution transmission electron microscopy. Pyrene is chosen as the pi - aromatic molecule; its dimer is covalently linked to the SWNT sidewalls by aryl addition. Reflecting the orientation and separation of the two molecules, the pyrene dimer on the SWNT exhibits characteristic optical and photophysical properties. The methodology discussed here-form and probe molecular dimers-is highly promising for the creation of unique models and provides indispensable and fundamental information regarding molecular interactions.