The great strides of perovskite-based photovoltaic devices galvanize an increasing number of material studies. We revealed the photoinduced steady-state free carrier densities of perovskite films through a purely optical detection method. The method avoided the possible interference from strong ionic conductivity within perovskite materials. The densities were measured at the order of 1015 cm−3 and 1016 cm−3 for CH3NH3PbI3 films without and with chlorine introduction, respectively. Long free carrier lifetimes were figured out according to the densities. The densities were found to increase, as observed from the illumination, following a sublinear power law. This indicates sub-bandgap trapping states involved in the charge accumulation mechanism. In addition, the densities presented an abnormal temperature sensitivity revealing a thermally activated recombination channel above ∼240 K.

A series of conductive polymers, i.e., poly(3-methylthiophene) (PMT), poly(thiophene) (PT), poly(3-bromothiophene) (PBT) and poly(3-chlorothiophene) (PCT), were prepared via the electrochemical polymerization process. Subsequently, their application as hole-transporting materials (HTMs) in CH3NH3PbI3 perovskite solar cells was explored. It was found that rationally increasing the work function of HTMs proves beneficial in improving the open circuit voltage (Voc) of the devices with an ITO/conductive-polymer/CH3NH3PbI3/C60/BCP/Ag structure. In addition, the higher-Voc devices with a higher-work-function HTM exhibited higher recombination resistances. The highest open circuit voltage of 1.04 V was obtained from devices with PCT, with a work function of–5.4 eV, as the hole-transporting layer. Its power conversion efficiency attained a value of approximately 16.5%, with a high fill factor of 0.764, an appreciable open voltage of 1.01 V and a short circuit current density of 21.4 mA·cm–2. This simple, controllable and low-cost manner of preparing HTMs will be beneficial to the production of large-area perovskite solar cells with a hole-transporting layer.

Ferroelectric materials exhibiting anomalous photovoltaic properties are one of the foci of photovoltaic research. We review the foundations and recent progress in ferroelectric materials for photovoltaic applications, including the physics of ferroelectricity, nature of ferroelectric thin films, characteristics and underlying mechanism of the ferroelectric photovoltaic effect, solar cells based on ferroelectric materials, and other related topics. These findings have important implications for improving the efficiency of photovoltaic cells.具有反常光伏效应的铁电材料是光伏研究的重点之一. 本文综述了铁电材料在光伏应用中的研究进展, 包括铁电性的物理基础、铁电薄膜的性质、铁电光伏效应的特点和内在机制、铁电材料太阳电池等. 这些发现对于进一步提高光伏电池的效率具有重要意义.

In the present work, a hole-conductor-free inverted-structure planar perovskite solar cell was fabricated by a solution process. Remarkably, the device showed a power conversion efficiency (PCE) up to 16.0%, which is higher than those of reported hole-conductor-free perovskite solar cells, and even higher than that of devices using NiOx as the hole conductor. Furthermore, the hole-conductor-free device was also found to reveal a very good stability.

This article demonstrates a significant broadband enhancement of light absorption and improvement of photon-generated-charge transfer in CH3NH3PbI3 perovskite solar cells by incorporating plasmonic Au–Ag alloy popcorn-shaped nanoparticles (NPs). Compared to conventional nanoparticles and nanorods, these popcorn-shaped NPs have many fine structures. The device's maximum power conversion efficiency (PCE) increases from 8.9% to 10.3%, namely 15.7% enhancement, with the aid of plasmonic popcorn-shaped NPs.

•Three emission bands of ANS–protein are located by transient spectroscopy.•Emission lifetime at surface of molten globular protein is concentration dependent.•No such dependency was found for wild-type protein bound ANS.•Continuously distributed surface hydrophobicity is suggested for MG proteins.•ANS is suitable to qualitatively compare surface hydrophobicity, not quantitatively.We studied the picosecond time-resolved fluorescent spectroscopy of 1-anilino-8-naphthalene sulfonate (ANS), which binds to the staphylococcal nuclease (SNase) of the wild-type (WT) and the molten globule (MG) state. Three ANS emission bands at ∼530 nm, ∼495 nm, and ∼475 nm are resolved, corresponding to three ANS states: the free ANS in solution and associated form adsorbing to surface sites and binding to active sites. The surface hydrophobicity of the WT is moderate and different from the MG state, as shown both in the position of the bands and by the concentration dependent ANS fluorescent decay. For MG, the decay of two blue bands accelerated with the increment of the ANS concentration, whereas the WT did not show this dependency. However, when pdTp, an inhibitor, was attached to the active site of the MG state, band 2 decay was also independent of the ANS concentration. These results indicate that the protein hydrophobic sites have two types of interactions with ANS.

Ultrathin polythiophene films prepared via electrochemical polymerization is successfully used as the hole-transporting material, substituting conventional HTM-PEDOT:PSS, in planar p-i-n CH3NH3PbI3 perovskite-based solar cells, affording a series of ITO/polythiophene/CH3NH3PbI3/C60/BCP/Ag devices. The ultrathin polythiophene film possesses good transmittance, high conductivity, a smooth surface, high wettability, compatibility with PbI2 DMF solution, and an energy level matching that of the CH3NH3PbI3 perovskite material. A promising power conversion efficiency of about 15.4%, featuring a high fill factor of 0.774, open voltage of 0.99 V, and short-circuit current density of 20.3 mA·cm−2 is obtained. The overall performance of the devices is superior to that of cells using PEDOT:PSS. The differences of solar cells with different hole-transfer materials in charge recombination, charge transport and transfer, and device stability are further investigated and demonstrate that polythiophene is a more effective and promising hole-transporting material. This work provides a simple, prompt, controllable, and economic approach for the preparation of an effective hole-transporting material, which undoubtedly offers an alternative method in the future industrial production of perovskite solar cells.

The steady-state absorption and fluorescence emission positions of diprotonated meso-tetrakis(4-sulfonatophenyl) porphyrin (H4TPPS2−) are dependent on the polarity of the selected two solid ionic liquids (ILs) and are red-shifted with the increase of cation size. The solvation dynamics process of H4TPPS2− in these ILs occurs on two well-separated time scales. The short components with 121.2–128.6 ps arise from the local motion of the ion-pairs in close proximity to the porphine core, and the long components with 1056.6–1261.8 ps are due to the collective translation motions of the ion-pairs. The dynamic Stokes shifts and the relaxation times increase with the increasing cation size of the ILs.

The ultrafast third-order nonlinear optical properties of graphene in both suspension and film status are studied using femtosecond time resolved optical Kerr gate technique at 800 nm. The third-order nonlinear optical susceptibility is 4.2 × 10−14 esu for solution of 0.010 mg/ml. The corresponding second-order hyperpolarizability is 3.4 × 10−32 esu per carbon atom in graphene, which is the largest among the carbon family. The graphene embed in the polymer matrix of polyvinyl alcohol film (OD = 0.43) exhibits strong ultrafast nonlinear optical response of 3.3 × 10−12 esu and shows its potential application in nonlinear optics.Graphical abstractHighlights► Ultrafast third-order nonlinear optics of graphene was investigated by OKE. ► γc Of graphene was determined to be 3.4 × 10−32 esu per carbon atom. ► The χ(3) of graphene/PVA film (OD = 0.52) was measured 3.1 × 10−12 esu.

Two-polymers, phenothiazine derivatives (PQ) and poly 2-methoxy-5-(2′-ethylhexyloxy)-1,4-phenylene vinylene (MEH-PPV), who show complementary absorption to the solar spectrum are blended for broader absorption. The energy transfer from PQ to MEH-PPV is designed and observed at ultrafast time scale of ∼2 ps. Föster resonance energy transfer (FRET) process is regarded as the mechanism. Band gap of PQ is determined as 2.5 eV. With this design, a ladder type energy transfer and collection is suggested.Graphical abstractHighlights► Blended polymer film with polymer blend with complementary absorption spectra. ► Ultrafast Föster resonance energy transfer (FRET) process from PQ to MEH-PPV. ► The FRET process takes place as fast as 2 ps.

We setup an ultrafast noncollinear optical parametric amplification system for fluorescence spectral dynamics study. The simultaneous broadband amplifying ability makes it suitable as an ultrafast spectrometer with femtosecond time-resolution. By real-time fluctuation correction, femtosecond fluorescence spectra are obtained efficiently by a single scan. With this technique, the solvation dynamics of DCM dye in four solvents are measured to demonstrate the performance of the system. We show that this ultrafast time-resolved spectrometer is very useful and efficient in studying ultrafast spectral dynamics.Research highlights► Femtosecond fluorescent spectrometer based on non-collinear parametric amplification. ► Full fluorescence spectral decay at femtosecond time resolution is achieved by single temporal scan. ► Spectral dynamics can be observed and studied directly in this spectrometer system.

Two-photon fluorescence (TPF) process is an important research subject and can be optimized by pulse shaping techniques. In addition to temporal femtosecond pulse shaping by spectral phase modulation, we take into account of spatial configuration in the shaping process. The TPF of Coumarin 500 increases 40% with this additional modulation step. This spatial modulation results in not only transverse spatial profile variation but also effect of temporal redistribution at focus. We show that this spatial modulation is an important dimension for pulse shaping and optimization for TPF.Research highlights► Two photon fluorescence of Coumarin 500 was optimized by combined temporal–spatial pulse shaping using a 2D phase modulator. ► When the spatial phase modulation was applied, the intensity of two photon fluorescence of Coumarin 500 can be further optimized by 40% in addition to temporal only pulses shaping. ► The spatial modulation results in not only spatial profile variation but also effect of temporal redistribution at focus.

We report herein the photophysics of three two-dimensional polythiophene derivatives, with different lengths of thienylene−vinylene conjugated side chains, in comparison with regioregular poly(3-hexylthiophene) (P3HT). In solution, an evolution from stimulated emission to photoinduced absorption (PIA) at emission peak is discovered with increasing length of side chains, indicating larger steric hindrance by longer side chains. The exciton lifetime is reduced by a factor of five when the thienylene−vinylene side chain is prolonged to three units. In the film form, we investigate the dynamics of the two PIA bands, assigned to intrachain exciton and interchain polaron pairs, respectively. The analysis of the dynamics suggests that their intrachain exciton decays are similar to the one-dimensional P3HT. The recombination possibility of delocalized interchain polaron pairs occurring in 0.9 ps is reduced with longer thienylene−vinylene side chain samples. Compared with regioregular P3HT film, which self-organizes to form lamellae crystal morphology, the morphologies of these three two-dimensional polythiophenes are amorphous, attributed to the large steric hindrance caused by the existence of side chains. This design of polythiophene derivatives provides the reduction of recombination possibility for delocalized interchain polaron pairs generated in the polymer.

The steady-state and transient photophysics of a series of newly synthesized phenothiazine-based conjugated polymers and copolymers with thiophene and furan moieties in solvents were investigated. Positive solvatochromism in emission spectra was observed in polar solvents due to excited-state intramolecular charge-transfer. The picosecond time-resolved spectra using streak camera revealed fast chain twisting motion at ∼10 ps, verified by solvent viscosity dependency. A non-radiative de-activate pathway is assigned to the non-planar conformation at excited state. This reveals a possible way for intramolecular energy loss in new polymer design for applications.

Charge-transfer composite material, poly-1-methoxy-4-octoxy-(para-phenelene vinylene) (MO-PPV) wrapped single wall carbon nanotubes (SWNTs), MO-PPV/SWNTs, was synthesized by in situ polymerization. Photophysics properties of MO-PPV/SWNTs were studied by using steady-state spectra, femtosecond fluorescence up-conversion technique, and streak camera. Compared with the pure MO-PPV in solution, fluorescence quenching was observed. Photoinduced electron-transfer from MO-PPV to SWNTs occurs on femtosecond timescale, while photoinduced intermolecular energy-transfer appears at ∼100 ps timescale.Static and transient researches on MO-PPV/SWNTs reveal ultrafast intermolecular electron-transfer. Slower exciton migration was also observed.

In the present work, a hole-conductor-free inverted-structure planar perovskite solar cell was fabricated by a solution process. Remarkably, the device showed a power conversion efficiency (PCE) up to 16.0%, which is higher than those of reported hole-conductor-free perovskite solar cells, and even higher than that of devices using NiOx as the hole conductor. Furthermore, the hole-conductor-free device was also found to reveal a very good stability.

The great strides of perovskite-based photovoltaic devices galvanize an increasing number of material studies. We revealed the photoinduced steady-state free carrier densities of perovskite films through a purely optical detection method. The method avoided the possible interference from strong ionic conductivity within perovskite materials. The densities were measured at the order of 1015 cm−3 and 1016 cm−3 for CH3NH3PbI3 films without and with chlorine introduction, respectively. Long free carrier lifetimes were figured out according to the densities. The densities were found to increase, as observed from the illumination, following a sublinear power law. This indicates sub-bandgap trapping states involved in the charge accumulation mechanism. In addition, the densities presented an abnormal temperature sensitivity revealing a thermally activated recombination channel above ∼240 K.