Flash-photolysis Time-resolved Microwave Conductivity Research Articles

Identification and Dynamics of Microsecond Long-Lived Charge Carriers for CsPbBr3 Perovskite Quantum Dots, Featuring Ambient Long-Term Stability.

We analyze the stability and photophysical dynamics of CsPbBr3 perovskite quantum dots (PeQDs), fabricated under mild synthetic conditions and embedded in an amorphous silica (SiOx) matrix (CsPbBr3@SiOx), underscoring their sustained performance in ambient conditions for over 300 days with minimal optical degradation. However, this stability comes at the cost of a reduced photoluminescence efficiency. Time-resolved spectroscopic analyses, including flash-photolysis time-resolved microwave conductivity and time-resolved photoluminescence, show that excitons in CsPbBr3@SiOx films decay within 2.5 ns, while charge carriers recombine over approximately 230 ns. This longevity of the charge carriers is due to photoinduced electron transfer to the SiOx matrix, enabling hole retention. The measured hole mobility in these PeQDs is 0.880 cm2 V-1 s-1, underscoring their potential in optoelectronic applications. This study highlights the role of the silica matrix in enhancing the durability of PeQDs in humid environments and modifying exciton dynamics and photoluminescence, providing valuable insights for developing robust optoelectronic materials.

Elucidation of a Photothermal Energy Conversion Mechanism in Hydrogenated Molybdenum Suboxide: Interplay of Trapped Charges and Their Dielectric Interactions

Hydrogenated molybdenum suboxide (HxMoO3-y) is a promising photothermal energy conversion (PEC) material. However, its charge carrier dynamics and underlying mechanisms remain unclear. Utilizing flash-photolysis time-resolved microwave conductivity, we investigated charge carrier-dielectric interactions in the Pt/HxMoO3-y composite. The charge recombination of H2-reduced Pt/HxMoO3-y was 2-3 orders of magnitude faster than that of Pt/MoO3, indicating efficient PEC. A complex photoconductivity study revealed that Pt/HxMoO3-y has two types of trapping mechanisms, Drude-Zener (DZ) and negative permittivity effect (NPE) modes, depending on the reduction temperature. Pt/HxMoO3-y reduced at 100 °C exhibited a dominant NPE owing to the electrical interaction of trapped charges with the surrounding ions and/or OH base. This polaronic trapped state retarded the PEC process. We found Pt/HxMoO3-y reduced at 200 °C to be optimal owing to the balanced suppression of the NPE and charge diffusion. This is the first report revealing the charge dynamics in hydrogenated metal oxides and their impacts on PEC processes.

Supramolecular Recognition within a Nanosized "Buckytrap" That Exhibits Substantial Photoconductivity.

We report here a nanosized "buckytrap", 1, constructed from two bis-zinc(II) expanded-TTF (exTTF) porphyrin subunits. Two forms, 1a and 1b, differing in the axial ligands, H2O vs tetrahydrofuran (THF), were isolated and characterized. Discrete host-guest inclusion complexes are formed upon treatment with fullerenes as inferred from a single-crystal X-ray structural analyses of 1a with C70. The fullerene is found to be encapsulated within the inner pseudohexagonal cavity of 1a. In contrast, the corresponding free-base derivative (2) was found to form infinite ball-and-socket type supramolecular organic frameworks (3D-SOFs) with fullerenes, (2•C60)n or (2•C70)n. This difference is ascribed to the fact that in 1a and 1b the axial positions are blocked by a H2O or THF ligand. Emission spectroscopic studies supported a 1:1 host-guest binding stoichiometry, allowing association constants of (2.0 ± 0.5) × 104 M-1 and (4.3 ± 0.9) × 104 M-1 to be calculated for C60 and C70, respectively. Flash-photolysis time-resolved microwave conductivity (FP-TRMC) studies of solid films of the Zn-complex 1a revealed that the intrinsic charge carrier transport, i.e., pseudo-photoconductivity (ϕ∑μ), increases upon fullerene inclusion (e.g., ϕ∑μ = 1.53 × 10-4 cm2 V-1 s-1 for C60⊂(1a)2 and ϕ∑μ = 1.45 × 10-4 cm2 V-1 s-1 for C70⊂(1a)2 vs ϕ∑μ = 2.49 × 10-5 cm2 V-1 s-1 for 1a) at 298 K. These findings provide support for the notion that controlling the nature of self-assembly supramolecular constructs formed from exTTF-porphyrin dimers through metalation or choice of fullerene can be used to regulate key functional features, including photoconductivity.

Preparation and Physicochemical Properties of Nanomaterial/Fullerene Composites

Bismuthene, an exfoliated two-dimensional material obtained from bulk bismuth, has drawn significant attention because of its unique electronic properties. Few-layered bismuthene (FLBi) with an average thickness of 1.0 nm was synthesized by the ball mill and sonication method. The FLBi film was fabricated onto a semiconducting SnO2 electrode by electrophoretic deposition (SnO2/FLBi). In the flash-photolysis time-resolved microwave conductivity measurement, the SnO2/FLBi film showed a rise of conductivity upon photoexcitation, supporting the occurrence of the electron injection from the photoexcited FLBi to the conduction band of SnO2. The SnO2/FLBi on a transparent fluorine-doped tin oxide (FTO) electrode was used for photoelectrochemical devices. Photocurrents produced by the FTO/SnO2/FLBi electrode were larger than those produced by the FTO/SnO2 and FTO/FLBi electrodes because of the efficient electron injection. Moreover, FLBi was noncovalently functionalized with fullerene C60 in a mixed solvent of toluene and acetonitrile. Upon photoexcitation, the composite of FLBi and C60 exclusively led to the occurrence of photoinduced energy transfer from C60 to FLBi without generating the charge-separated state. These results give fundamental insights into the feasibility toward the construction of FLBi-based optoelectronic devices.Supramolecular composites consisting of fullerene C60 and carbon nanodiamond (ND) were prepared through spontaneous complexation of C60 aggregates onto the surface of ND aggregates in N-methylpyrrolidone. The resultant C60-ND composite was fabricated onto a nanostructured SnO2 electrode by an electrophoretic deposition method. Formation of the C60-ND composite was supported by dynamic light scattering and field-emission scanning electron microscopy. The C60-ND composite on the SnO2 electrode revealed high incident photon-to-current efficiencies in the visible region in comparison with the single component system of C60 or ND. The enhanced photocurrent generation of the C60-ND composite may originate from the photoinduced charge separation at the interface between C60 and ND. These results will give important insight into the design of all-nanocarbon optoelectronic devices.[1] T. Umeyama, Y. Okawada, T. Ohara, and H. Imahori, Chem. Asian J., 14, 4042-4047 (2019).[2] T. Umeyama, H. Xu, T. Ohara, Y. Tsutsui, S. Seki, H. Imahori, J. Phys. Chem. C, 125, 13954-13962 (2021).

(Invited, Digital Presentation) Composites of 2D Materials and Organic Molecules

Atomically thin two-dimensional (2D) materials have aroused an explosive growth of scientific interest for their outstanding physicochemical properties. In addition, decorations of 2D materials with organic semiconductors have also begun to receive scientific attention owing to the tunable optoelectronic properties and the excellent solution-based processability of the organic molecules. In this study, composite films that consisted of C60 with well-exfoliated nanosheets of transition metal dichalcogenides (TMDs) [1], antimony [2], or bismuth [3] were successfully 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. In addition, photophysical and photoelectrochemical properties of the composite films were investigated in detail. For example, in a flash-photolysis time-resolved microwave conductivity (FP-TRMC) measurement of a composite material consisting of C60 and few-layered antimonene (FLSb) nanosheets (denoted as (FLSb+C60) m ), a rapid rise in transient conductivity was observed, whereas no conductivity signal was observed in the single components, FLSb and C60. This demonstrated the occurrence of photoinduced charge separation between FLSb and C60 in (FLSb+C60) m . Furthermore, a photoelectrochemical device with an electrophoretically deposited (FLSb+C60) m film exhibited an enhanced efficiency of photocurrent generation, compared to those of the single-components, FLSb and C60, due to the photoinduced charge separation between FLSb and C60. This work provides a promising approach for fabrication of 2D material–organic molecule composites and paves the way for their application in optoelectronics.[1] J. Baek, T. Umeyama, W. Choi, Y. Tsutsui, H. Yamada, S. Seki, and H. Imahori, Chem. Eur. J., 24, 1561-1572 (2018).[2] T. Umeyama, T. Ohara, Y. Tsutsui, S. Nakano, S. Seki, and H. Imahori, Chem. Eur. J., 26, 6726-6735 (2020).[3] T. Umeyama, H. Xu, T. Ohara, Y. Tsutsui, S. Seki, and H. Imahori, J. Phys. Chem. C, 125, 13954-13962 (2021).

Controlling the charge carrier dynamics by modulating the orientation diversity of perovskites

Photo-induced charge carrier dynamics over a wide time domain from sub-nanoseconds to microseconds, via time-correlated single photon counting and flash photolysis time-resolved microwave conductivity measurements.

Crystal Lattice Design of H2O-Tolerant n-Type Semiconducting Dianionic Naphthalenediimide Derivatives.

Dianionic bis(propionate)-naphthalenediimide (PCNDI2-) formed simple 2:1 cation-anion salts of (M+)2(PCNDI2-)·(H2O)n (M+ = Li+, Na+, K+, Rb+, and Cs+), which exhibited reversible H2O adsorption-desorption behavior because of the presence of their electrostatically binding crystal lattices. The maximum H2O adsorption amounts (n) for M+ = Li+, Na+, K+, Rb+, and Cs+ were 0.25, 6.0, 4.0, 6.0, and 2.0, respectively, whereas the reversible gate-opening (gate-closing) H2O adsorption-desorption isotherms were observed at 273 and 298 K, except for M+ = Li+. High ionic conductivities of around 10-4-10-5 S cm-1 were observed in M+ = Na+ and K+ salts, whereas short-range thermal fluctuations occurred in large cations of M+ = Rb+ and Cs+. The change in the electrostatic lattice energy for M+ = Na+ and K+ salts during the H2O adsorption-desorption cycles was significantly larger than those for M+ = Rb+ and Cs+. Therefore, the Na+ and K+ salts had a considerably flexible electrostatic crystal lattice with a large amplitude of lattice modulation during the H2O sorption cycle. In contrast, the lattice modulation for M+ = Rb+ and Cs+ salts involved a low magnitude of ion displacements, forming a relatively rigid cation-anion electrostatic crystal lattice. The flash-photolysis time-resolved microwave conductivity and transition absorption spectroscopy results revealed the high electron mobility of H2O-adsorbed thin films, wherein the crystallized H2O molecules did not act as electron-trapping sites. The values of electron mobility increased in the order of Cs+ ≈ Rb+ > K+ > Na+ > Li+.

Towards Macroscopically Anisotropic Functionality: Oriented Metallo-supramolecular Polymeric Materials Induced by Magnetic Fields.

Based on the predesigned self-selective complexation, metallo-supramolecular P3HT-b-PEO diblock copolymers with varying block ratios were synthesized, and their oriented polymer films generated during solvent evaporation in a 9 T magnetic field were investigated. An anisotropic, ordered layer structure was achieved using [P3HT20 -Zn-PEO107 ] and carefully characterized by polarized optical microscopy (POM), AFM, polarized UV/Vis spectroscopy, and GI-SAXS/WAXS. The PEO-removed [P3HT20 -Zn-PEO107 ] film was obtained after decomplexation with TEA-EDTA under mild conditions, and the selective removal of PEO domains was evidenced by UV/Vis and ATR-FTIR spectroscopy. Anisotropic photoconductivity of the magnetically aligned film was evaluated by flash-photolysis time-resolved microwave conductivity (FP-TRMC) measurements. The results indicated that the presence of insulating crystalline PEO segments diminished the photoconductivity along the P3HT backbone direction.

Towards Macroscopically Anisotropic Functionality: Oriented Metallo‐supramolecular Polymeric Materials Induced by Magnetic Fields

AbstractBased on the predesigned self‐selective complexation, metallo‐supramolecular P3HT‐b‐PEO diblock copolymers with varying block ratios were synthesized, and their oriented polymer films generated during solvent evaporation in a 9 T magnetic field were investigated. An anisotropic, ordered layer structure was achieved using [P3HT20‐Zn‐PEO107] and carefully characterized by polarized optical microscopy (POM), AFM, polarized UV/Vis spectroscopy, and GI‐SAXS/WAXS. The PEO‐removed [P3HT20‐Zn‐PEO107] film was obtained after decomplexation with TEA‐EDTA under mild conditions, and the selective removal of PEO domains was evidenced by UV/Vis and ATR‐FTIR spectroscopy. Anisotropic photoconductivity of the magnetically aligned film was evaluated by flash‐photolysis time‐resolved microwave conductivity (FP‐TRMC) measurements. The results indicated that the presence of insulating crystalline PEO segments diminished the photoconductivity along the P3HT backbone direction.

Modulation of Band Gaps toward Varying Conductivities in Heterometallic One-Dimensional Chains by Ligand Alteration and Third Metal Insertion

A heterometallic one-dimensional (1-D) chain consisting of multiple kinds of metals, Rh, Pt, and Pd, with direct metal–metal bonds was successfully obtained by mixing a Rh dinuclear complex and Pt–Pd–Pt trinuclear complex. The Pt–Pd–Pt trinuclear complex can be reversibly one-electron-oxidized or -reduced, where the electron paramagnetic resonance spectrum of the one-electron-oxidized one shows an axially symmetric signal with hyperfine splitting by two Pt and Pd, indicating that an unpaired electron is delocalized to the dz2 orbital of Pt–Pd–Pt. Utilized with the highest occupied molecular orbital and lowest unoccupied molecular orbital interaction at the dz2 orbital, simple mixing of the Pt–Pd–Pt trinuclear complex and Rh dinuclear complex in adequate solvents afforded heterometallic 1-D chains, which are aligned as −Rh–Rh–Pt–Pd–Pt–. Several physical measurements revealed that the metal oxidation state is +2. Diffuse reflectance spectra and theoretical calculations show that heterometallic 1-D chains have σ-type conduction and valence bands where π*(Rh2) are lying between them, whose gaps become narrower than the prototype chains aligned as −Rh–Rh–Pt–Pt–Pt–Pt–. The narrower band gaps are induced by destabilization of the σ-type valence bands and accompanied by insertion of Pd ions because the d-orbital energy level of Pd is closer in value to Rh compared with Pt. Flash-photolysis time-resolved microwave conductivity measurements exhibited an increase in the product of charge carrier mobility and its generation efficiency (8.1 × 10–5 to 4.6 × 10–4 cm2 V–1 s–1) with narrowing the band gaps, suggesting that the better conductivity is attributed to shorter metal–metal distances in 1-D chains. These results imply the possibilities of controlling band gap with ligand modification and third metal insertion in heterometallic 1-D chains to show various conductivities.

Ultrathin Two Dimensional (2D) Supramolecular Assembly and Anisotropic Conductivity of an Amphiphilic Naphthalene-Diimide.

Two-dimensional (2D)-supramolecular assemblies of π-conjugated chromophores are relatively less common compared to a large number of recent examples on their low dimensional (0D or 1D) assemblies or 3D architectures. This article reports a rational design for the 2D supramolecular assembly of an amphiphilic core-substituted naphthalene-diimide derivative (cNDI-1). The building block contains a naphthalene-diimide (NDI) chromophore, symmetrically substituted with two dodecyl chains from the aromatic core while the imide positions are functionalized with two hydrophilic wedges containing oligo-oxyethylene chains. In water, it exhibits entropically favorable self-assembly with a critical aggregation concentration of 1.5 × 10-5 M and a lower critical solution temperature of 55 °C. The UV/vis absorption spectrum in water shows bathochromically shifted absorption bands compared to that of the monomeric dye in THF, indicating offset π-stacking among the NDI chromophores. C-H symmetric and asymmetric stretching frequencies in the FT-IR spectrum support the presence of organized hydrocarbon chains in trans conformation in the self-assembled state, similar to that in the crystalline n-alkanes, which is further supported by studying the general polarization (GP) values of a noncovalently entrapped Laurdan dye. The atomic force microscopy (AFM) image shows the formation of ultrathin (height < 2.0 nm) ribbons for the spontaneously assembled sample which eventually produces a large-area 2D nanosheet by the lateral organization. The powder X-ray diffraction pattern of the drop-casted film, prepared from the preformed aggregates, reveals sharp peaks that indicate a crystalline lamellar packing along the direction of the 2D growth. Differential scanning calorimetry trace shows the melting of the crystalline alkyl chain domain at T > 75 °C, which destroys the 2D assembly. Local-scale photoconductivity of the ordered 2D assembly, studied by the flash-photolysis time-resolved microwave conductivity (FP-TRMC) technique, reveals an anisotropic conductivity with ∼3 times larger conductivity along the parallel direction compared to that along the perpendicular one.

Noncovalent Functionalization of Few-Layered Antimonene with Fullerene Clusters and Photoinduced Charge Separation in the Composite.

Few-layered antimonene (FLSb) nanosheets were noncovalently functionalized with fullerene C60 clusters by quick addition of a poor solvent (i.e., acetonitrile) into a mixed dispersion of FLSb and C60 in a good solvent (i.e., toluene). In a flash-photolysis time-resolved microwave conductivity (FP-TRMC) measurement, the FLSb-C60 composite, (FLSb+C60 )m , showed a rapid rise in transient conductivity, whereas no conductivity signal was observed in the single components, FLSb and C60 . This demonstrated the occurrence of photoinduced charge separation between FLSb and C60 in (FLSb+C60 )m . Furthermore, a photoelectrochemical device with an electrophoretically deposited (FLSb+C60 )m film exhibited an enhanced efficiency of photocurrent generation, compared to those of the single-components, FLSb and C60 , due to the photoinduced charge separation between FLSb and C60 . This work provides a promising approach for fabrication of antimonene-organic molecule composites and paves the way for their application in optoelectronics.

Naphthalenediimide (NDI)‐Conjugated Foldable Polyurethanes: Impact of Chromophoric Location on Hierarchical Supramolecular Assembly and Conductivity

AbstractThe manuscript reports supramolecular assembly and photophysical properties of two polyurethanes (P1, P2) with appended naphthalene‐diimide (NDI) chromophore which serves as a n‐type semiconductor. P1 and P2 are constitutional isomers and they differ in the location of the NDI moiety. In P1, NDI is a part of the polymer backbone (placed between the two urethane groups in each repeating unit) while in P2, it remains as a pendant group. In a non‐polar solvent like tetra‐chloroethylene (TCE), both adopt a pleated structure driven by intra‐chain H‐bonding among the urethane groups. Subsequently the secondary structure of P2 assembles to a meta‐stable spherical structure (similar to polymersome) which after 70–75 h transforms to nanotubes with the folded polymer chains constructing the wall of the tube. In sharp contrast, the intra‐chain folded conformation of P1, owing to its enhanced rigidity contributed by the synergistic π‐stacking and H‐bonding, does not get trapped in the spherical intermediate, but spontaneously grows to fibrils leading to macroscopic gelation within 30 min. Flash‐photolysis time‐resolved microwave conductivity (FP‐TRMC) measurements together with transient absorption spectroscopy studies revealed remarkably high charge carrier mobility (3×10−3 cm2 V−1 s−1) which can be attributed to the long range stacking order of the NDI chromophores in the fibrillar assembly of P1 while for the nanotubular structure of P2, the value was almost an order of magnitude less reflecting importance of the mesoscopic structure on generation of percolated pathway for efficient charge transport.

Peripherally Cyanated Subphthalocyanines as Potential n-Type Organic Semiconductors.

A series of peripherally dicyano-, tricyano-, and tetracyano-substituted subphthalocyanines (SubPcs) have been prepared through microwave-assisted, palladium-mediated cyanation of iodinated precursors. The introduction of π-accepting cyano groups in the macrocycle clearly influences its electronic and redox properties, which are dependent on the number and relative position of these substituents. Additional functionalization of the periphery of SubPcs with electron-donating or -withdrawing groups allows for a further fine-tuning of their features, leading to intensely absorbing, strongly electron-accepting panchromatic dyes with low-lying LUMO energy levels. Flash-photolysis time-resolved microwave conductivity measurements on vapor-deposited films demonstrate that some of these novel SubPc derivatives display remarkable intrinsic charge-carrier mobilities that are comparable to or larger than those of other known well-performing acceptor SubPcs; thus confirming their potential as n-type organic semiconductors for application in the fabrication of photovoltaic devices.

Durian-Shaped CdS@ZnSe Core@Mesoporous-Shell Nanoparticles for Enhanced and Sustainable Photocatalytic Hydrogen Evolution.

In artificial photosynthesis, the establishment of design guidelines for nanostructures to maximize the photocatalytic performance remains a great challenge. In contrast with the intense research into band-offset tuning for photocatalysts, the relationship between nanostructures and photoinduced carrier dynamics has still been insufficiently explored. We synthesized durian-shaped CdS@ZnSe core@mesporous-shell nanoparticles ( d-CdS/ZnSe NPs) and investigated the carrier dynamics in photocatalytic hydrogen evolution. The cocatalyst-free d-CdS/ZnSe NPs exhibited high photocatalytic activity for H2 evolution (14.8% apparent quantum yield at 420 nm) and excellent stability (maintaining 80% activity after 72 h) under visible-light irradiation (>422 nm). The transient absorption measurement and flash photolysis time-resolved microwave conductivity unveiled that the ultra-long-lived charge separation (>6.2 ms) and swift hole transfer to the surfaces of ZnSe shell (11 ns) contribute the high catalytic activity and stability. The present work provides a novel insight into designing nanoparticulate photocatalysts with optimized performance.

Supramolecular Chirality Issues in Unorthodox Naphthalene Diimide Gelators

Herein, the self-assembly of a few 1,3-dihydroxyl functionalized naphthalene diimide (NDI) derivatives has been reported with particular emphasis on the impact of chirality on gelation and the effect of self-assembly on charge-carrier mobility. A nonconventional gelator (R)-NDI, devoid of any long alkyl chains, exhibited spontaneous gelation in tetra-chloroethylene (TCE). Based on X-ray crystallography and powder X-ray diffraction studies, it was established that a ladder-like hydrogen-bonded chain formation between the 1,3-dihydroxyl group leads to the fibrillar structures with preferential helicity. Likewise the (S)-isomer also exhibited identical gelation and mesoscopic structure but produced fibrils with the opposite handedness. Intriguingly, an equimolar mixture of the (R)- and (S)-isomers did not show any gelation ability, rather a macroscopic precipitation was observed and, in sharp contrast to the individual isomers, the morphology of the mixture showed ill-defined near spherical agglomerates. Differential scanning calorimetry (DSC) studies revealed an identical crystallization peak for the supramolecular polymer produced from the enantiopure gelators ((R)- or (S)-isomer), which was absent in their equimolar mixture. However, mixtures of the two isomers with enantiomeric excess retrieved the gelation ability and preferential helicity demonstrating that chiral amplification is operative in the present system through the so-called "majority rule" effect. Chirality induction was also realized by the "sergeant and soldier" principle in the supramolecular assembly of an achiral NDI gelator in the presence of either the (R)- or (S)-isomer as the chiral dopant. However, the strong helical bias induced by the chiral gelator was found to be opposite in nature compared to that found in the self-assembly of the pure chiral gelator that has been rarely reported in the literature. Flash-photolysis time-resolved microwave conductivity (FP-TRMC) measurements indicated the strong positive impact of the gelation on the electrical conductivity.

Minute-Scale Degradation and Shift of Valence-Band Maxima of (CH3NH3)SnI3 and HC(NH2)2SnI3 Perovskites upon Air Exposure

The development of lead-free, tin-based perovskite solar cells is becoming a pervasive topic; however, the inherent instabilities of such cells have prevented a boost of their power conversion efficiency and a deeper understanding of their fundamental properties. By using the photoelectron yield spectroscopy (PYS) and flash-photolysis time-resolved microwave conductivity (TRMC) techniques, we investigate the effects of air exposure on the valence-band maxima (VBMs) and photoconductivities of tin iodide perovskites (methylammonium cation, MASnI3; formamidinium cation, FASnI3). These perovskites exhibit a shift of the VBM (e.g., from −5.02 eV at 0 min to −5.17 eV at 18 min), deterioration of the PYS profiles, and progressive decrease of the TRMC transients on the minute scale of air exposure. The addition of SnF2 was found to suppress the initial defect-related density of the filled electronic states of MASnI3 and FASnI3, as revealed by PYS, and to partly mitigate the degradation of MASnI3, as revealed by T...

Highly efficient air-stable/hysteresis-free flexible inverted-type planar perovskite and organic solar cells employing a small molecular organic hole transporting material

To acknowledge exceptionally productive flexible perovskite solar cells, low-temperature-processable efficient organic hole transporting materials are very significant for the emerging photovoltaic research. A new organic small molecular hole transporting material (N-(4-(9H-carbazol-9-yl)phenyl)-7-(4-(bis(4-methoxyphenyl)amino)phenyl)-N-(7-(4-(bis(4-methoxyphenyl)amino)phenyl)-9,9-dioctyl-9H-fluoren-2-yl)-9,9-dioctyl-9H-fluoren-2-amine (CzPAF-TPA)) has been rationally designed and synthesized for both highly efficient solution-processed flexible and rigid inverted-type planar heterojunction perovskite solar cells (i-PSCs) and flexible and rigid bulk heterojunction inverted organic solar cells (BHJ IOSCs). The dopant-free CzPAF-TPA-based device displayed significantly improved device performance in solution-processed flexible i-PSCs and flexible BHJ IOSCs with power conversion efficiencies (PCEs) of 12.46% and 7.52%, respectively, with negligible hysteresis, which is superior to that of standard HTM. Furthermore, the high PCE was recorded on rigid ITO substrate in dopant-free i-PSCs (PCE ~ 15.71%) and BHJ IOSCs (PCE ~ 8.74%). Notably, the promising technique of flash-photolysis time-resolved microwave conductivity was also well correlated with the obtained results. In addition to their high device performance in flexible as well as rigid i-PSCs and flexible BHJ IOSCs, they also showed long-term stability over 500h and 30 days with minimal loss of initial performance.

Temperature Dependence of Anisotropic Transient Conductivity of a La@C2v-C82(Ad) Crystal

The temperature dependence of the anisotropic transient conductivity of a La@C2v-C82(Ad) crystal was investigated using flash-photolysis time-resolved microwave conductivity (FP-TRMC) measurements. Results showed that the transient conductivity along the c-axis of the single-crystal increased as the temperature decreased, proving that electron transport can be described by the electronic band-conduction model instead of the electron-hopping model.

Recombination Dynamics in Thin-film Photovoltaic Materials via Time-resolved Microwave Conductivity

A method for investigating recombination dynamics of photo-induced charge carriers in thin film semiconductors, specifically in photovoltaic materials such as organo-lead halide perovskites is presented. The perovskite film thickness and absorption coefficient are initially characterized by profilometry and UV-VIS absorption spectroscopy. Calibration of both laser power and cavity sensitivity is described in detail. A protocol for performing Flash-photolysis Time Resolved Microwave Conductivity (TRMC) experiments, a non-contact method of determining the conductivity of a material, is presented. A process for identifying the real and imaginary components of the complex conductivity by performing TRMC as a function of microwave frequency is given. Charge carrier dynamics are determined under different excitation regimes (including both power and wavelength). Techniques for distinguishing between direct and trap-mediated decay processes are presented and discussed. Results are modelled and interpreted with reference to a general kinetic model of photoinduced charge carriers in a semiconductor. The techniques described are applicable to a wide range of optoelectronic materials, including organic and inorganic photovoltaic materials, nanoparticles, and conducting/semiconducting thin films.