Breaking the symmetry of a crystal structure can enable even-order nonlinear activities, including second-harmonic generation (SHG). The emerging chiral hybrid organic–inorganic metal halides feature unique optical and electronic properties and flexible crystal structures, making them a class of promising nonlinear optical materials. However, their nonlinear response performances are currently inferior to traditional nonlinear crystals, because of the lack of research on resonant enhancement and third-harmonic generation (THG). Herein, we designed chiral hybrid bismuth halides with naturally nonsymmetrical structure to enable SHG. Simultaneously, these chiral compounds preserve 1D crystal structures to create strong free exciton, broad self-trapped exciton (STE), and discrete band energy levels, which facilitate the resonant enhancement of SHG and THG susceptibilities. These new chiral films showcase superior effective SHG susceptibility (χ(2) ∼ 130.5 pm V–1 at an interesting wavelength of 1550 nm), exceeding that of the reference, a commercial LiNbO3 (χ(2) ∼ 83.4 pm V–1) single-crystal film. Furthermore, their THG intensities are even higher than their SHG intensities, with effective THG susceptibility (χ(3)) being ∼9.0 × 106 pm2 V–2 at 1550 nm (37 times that of the reference monolayer WS2). Their high SHG and THG performances indicate the promising future of these 1D chiral hybrid bismuth halides toward nonlinear optical applications.

The excitonic effect and JDOS dominated evolution in layer-dependent dielectric and optical properties of 2D WSe2 were investigated by spectroscopic ellipsometry.

Semitransparent organic solar cells (STOSCs) show great potential for application as power generating windows for buildings. The power conversion efficiency (PCE) and the average visible transmittance (AVT) are both important parameters with which to evaluate the overall performance of STOSCs. However, it is very challenging to simultaneously improve these two performance parameters because they are intrinsically contradictory to each other. In this work, the optical and photovoltaic properties of STOSCs are investigated based on two model samples including PTB7‐Th:PC61BM and PTB7‐Th:PC71BM by systematically tuning their device structures. By combining optical modeling and experimental results, a full optical analysis is provided for the STOSCs with details on photon harvesting, optical losses, transmission properties, energy distribution spectrum, electric field intensity distribution, and photon absorption rate distribution within the devices. Defined as the sum of the external quantum efficiency and the transmittance, the term “quantum utilization efficiency” is used as a subjective parameter to describe the light energy use in the semitransparent devices, which provides an alternative angle for analyzing STOSCs.

absorption intensity of active layers. [5][6][7][8][9][10] However, the performance of OSCs still inferior to other photovoltaic technologies due to several intrinsic defects (e.g., the thermalization losses of high energy photons and the transmission losses of low energy photons). To overcome these intrinsic losses of OSCs and enhance the PCE, one promising approach is adopting tandem structure. This type of device has two or more subcells stacked in series with complementary light absorption spectrum, in which the thermalization losses can be reduced by the utilization of high energy photons in front cell with widebandgap active layer and the transmission losses can be reduced by the utilization of low energy photons in back cell with narrow-bandgap active layer. [11][12][13][14] Thus, both the high energy and low energy photos can be utilized to generate photocurrent. Generally, the open-circuit voltage (V oc ) of tandem OSC should be the sum of subcells's V oc , while the short-circuit current density (J sc ) is restricted by the minimum J sc of subcells. [15][16][17][18] Thus, another striking advantage of tandem structure OSCs is that it exhibits a relatively low photocurrent and thus is favorable for achieving efficient large area module OSCs, since the power loss on the series resistance in large area electrode (can be simply expressed by Ohm's law, P R = I 2 R s , where the I is current while R s is the series resistance) will be obviously suppressed due to the lower photocurrent. [19][20][21][22] To achieve high performance tandem OSCs, much effort has been dedicated to the rational molecular design of materials with complementary absorption spectrum that are suitable for high performance subcell active layer. [23][24][25] Thanks to the significant progress of recently emerged nonfullerene acceptors with easily tunable absorption spectra, more complementary spectrum of both subcells can be obtained by utilizing nonfullerene-based active layer, and very promising tandem OSCs have been achieved. [26,27] In addition to the attentively researched novel pair of active layers in different subcells, the construction of interconnecting layer (ICL) also plays a critical role in achieving high performance tandem device. In general, the ICL is composed of a hole In the field of organic solar cells (OSCs), tandem structure devices exhibit very attractive advantages for improving power conversion efficiency (PCE). In addition to the well researched novel pair of active layers in different subcells, the construction of interconnecting layer (ICL) also plays a critical role in achieving high performance tandem devices. In this work, a new way of achieving environmentally friendly solvent processed polymeric ICL by adopting poly[(9,9-bis(3′-(N,N-dimethylamino)propyl)-2,7-fluorene)-alt-5,5′-bis(2,2′-thiophene)-2,6-naphthalene-1,4,5,8-tetracaboxylic-N,N′-di(2ethylhexyl)imide] (PNDIT-F3N) blended with poly(ethyleneimine) (PEI) as the electron transport layer (ETL) and PEDOT:PSS as the hole transport layer is reported. It ...

Accurate measurement of the Mueller matrix over a broad band is highly desirable for the characterization of nanostructures and nanomaterials. In this paper, we propose a general composite waveplate (GCW) that consists of multiple waveplates with flexibly oriented axes as a polarization modulating component in the Mueller matrix ellipsometer (MME). Although it is acommon practice to make achromatic retarders by combining multiple waveplates, the novelty of the GCW is that both the retardances and azimuths of fast axes of the single-waveplates in the GCW are flexible parameters to be optimized, which is different from the conventional design where single-waveplates are usually arranged in symmetrical layout or with their fast axes parallel or perpendicular to each other. Consequently, the GCW can provide many more flexibilities to adapt to the optimization of the MME over a broad band. A quartz triplate, as a concrete example of the GCW, is designed and used in a house-made MME. The experimental results on the air demonstrate that the house-made MME using the optimally designed quartz triplates has an accuracy better than 0.2% and a precision better than 0.1% in the Mueller matrix measurement over a broad spectral range of 200∼1000 nm. The house-made MME exhibits high measurement repeatability better than 0.004 nm in testing a series of standard SiO 2 /Si samples with nominal oxide layer thicknesses ranging from 2 nm to 1000 nm.

The complex optical conductivities of two-dimensaionl (2D) materials are fundamental for extended applications of related optoelectronic devices. Here, we systematically investigate the layer-dependent evolutions in the complex optical conductivities of 1–6 layer 2D MoS2 over an ultrawide spectral range (0.73–6.42 eV) by spectroscopic ellipsometry. We identify five feature peaks (A–E) in the optical conductivity spectra, which present interesting layer dependencies due to the scaling effect. Results suggest that the center energies of peaks A and B are nearly layer-independent, while those of peaks C and D exhibit redshifts as the layer increases. We interpret these layer-dependent evolutions as the competition between the decreasing exciton effect and the prominent band shrinkage with the increasing layer number. Additionally, the applicability of the classical slab model and the surface current model in evaluating the optical conductivities of 2D MoS2 with different layers is discussed from an experimental perspective.

By optimizing linear and stereoscopic structure of emitter to obtain preferential horizontal orientation, a high EQE green device of 30.0% based on IndCzpTr-2 was realized.

high photoluminescence (PL) quantum yield, narrow emission wavelength bandwidth, size-controllable emission wavelength, and easy material acquirement, as well as the solution-processed manufacture, make QLEDs a star, following the contemporary organic light-emitting diodes. [1][2][3] However, the development of high-performance FQLEDs is much slower, lagging behind their counterparts on glass substrates. For example, the reported highest current efficiency (CE) of red FQLEDs is below 17 cd A −1 and the maximum external quantum efficiency (EQE) is about 14%, [4,5] far behind 18% of the QLED on a glass substrate with similar inverted structure. [6] The main reasons can be attributed to the inferior mechanical performance of indium tin oxide (ITO) transparent conductive electrodes (TCEs) on plastic substrates and the refractive-index mismatch-induced severe total internal reflection (TIR) light loss in the QLED stack. [7,8] The brittle nature of ITO runs counter to good flexibility, and many efforts have been devoted to replace it with graphene, [9] silver nanowires (AgNWs), [10,11] and poly(3,4-ethylen edioxythiophene):poly(styrenesulfonate) [12,13] as flexible TCEs. On the other side, the refractive index of the commonly used plastic substrates (≈1.5) is much lower than ITO (1.8-2.1) in a standard substrate-emitting architecture, which goes against effective light extraction into the viewing domain, and it will consume ≈40% and ≈20% of the total-emitting light in the waveguide mode and substrate mode, respectively. [14,15] Numerous attempts have been made to enhance light outcoupling efficiency, such as using microlens arrays and scattering microspheres, to extract the trapped light in the substrate mode, [16,17] using photonic crystals or optical gratings, [18][19][20] high-index substrates, [21,22] low-index grids, [23] and structured TCEs, [7,24] to extract the waveguided light. However, all of these light extraction methods need complicated processing procedures.Embedding AgNWs network into polymer substrate is an ideal strategy for solving the aforementioned issues. The robust composite can afford repeated bending even folding, [25][26][27][28] and the AgNWs as light-scattering centers can enhance the light outcoupling efficiency. Furthermore, the reduced light Flexible quantum dot light-emitting diodes (FQLEDs) always suffer poor performance, and current efforts towards performance improvement need complicated procedures but still ending with limited progress. An extremely efficient and simply structured FQLED is demonstrated profited from the substantially enhanced light outcoupling efficiency by employing solutionprocessed flexible silver nanowires (AgNWs) transparent conductive electrodes (TCEs). As is uncovered by rigorous simulations, AgNWs TCEs extract enormous light trapped in the substrate mode and waveguide mode compared with indium tin oxide (ITO) TCEs, which greatly agrees with the experimental measurements in this work. As an ultimate achievement, the FQLED shows the record-breaking maximum exter...