Understanding the role of interconnecting layer on determining monolithic perovskite/organic tandem device carrier recombination properties

As one of the core parts of two-terminal(2 T) monolithic tandem photovoltaics, the interconnecting layers(ICLs) play a critical role in modulating the carrier transport and recombination between the sub-cells,and thus influencing the tandem device performance. Here, for the first time, the relationship between ICLs architecture and 2 T monolithic perovskite/organic tandem device performance has been studied by investigating the change of ICLs composition layer thickness on the ICLs optical and electrical properties, sub-cells EQE properties, and tandem device J-V properties. It is revealed that the ability of ICLs on modulating the sub-cells carrier balance properties is strongly associated with its composited layers thickness, and the tandem device carrier balance properties can be reflected by the relative EQE intensity between the sub-cells. Finally, with a deep understanding of the mechanisms, rational design of ICLs can be made to benefit the tandem device development. Based on the optimized ICL a high PCE of 20.03% is achieved.

Surface photovoltage phase spectroscopy study of the photo-induced charge carrier properties of TiO_(2) nanotube arrays

By using the surface photovoltage (SPV) technique based on a lock-in amplifier, surface states located 3.1 eV below the conduction band of TiO_(2) have been detected in TiO_(2) nanotube arrays prepared by anodization of titanium foil in fluoride-based ethylene glycol solution. The photo-induced charge transportation behavior of TiO_(2) nanotube arrays was also studied by quali- tatively analyzing their SPV phase spectra measured under different external bias. When a negative bias was applied, carriers excited from surface states have the same transportation properties as those excited from the valence band; in contrast, when a positive bias was applied, these two kinds of photo-excited carriers exhibit different transportation behavior..

Characterization of geometry and depleting carrier dependence of active silicon waveguide in tailoring optical properties

Changes in refractive index and the corresponding changes in the characteristics of an optical waveguide in enabling propagation of light are the basis for many modern silicon photonic devices. Optical properties of these active nanoscale waveguides are sensitive to the little changes in geometry, external injection/biasing, and doping profiles, and can be crucial in design and manufacturing processes. This paper brings the active silicon waveguide for complete characterization of various distinctive guiding parameters, including perturbation in real and imaginary refractive index, mode loss, group velocity dispersion, and bending loss, which can be instrumental in developing optimal design specifications for various application-centric active silicon waveguides.

Concerted regulation on vertical orientation and film quality of two-dimensional ruddlesden-popper perovskite layer for efficient solar cells

Recently,the two-dimensional(2D)ruddlesden-popper(RPP)perovskite has been successfully attracting great attention owing to their excellent electronic property and superior ambient stability.But 2D perovskite solar cells(PVSCs)with insulating large cations show a worse performance than three-dimensional(3D)PVSCs in general because of the worse charge transportation.In this work,dimethyl sulfoxide(DMSO)and KI were incorporated simultaneously to produce a synergistic effect on both film quality and orientation of 2D perovskite.With this strategy,a cavity-free 2D perovskite film was formed with vertically oriented crystal,and high quality film was obtained with decreased defects and increased crystallinity.Besides,profitable multiple phases were obtained for better spontaneous carrier separation and transportation.The 2D PVSCs based on(PEA)2(MA)n−1PbnI3n+1(n=5)delivered a higher power conversion efficiency(PCE)of 13.4%.In addition,the perovskite with KI and DMSO contained more stable low-dimension phase at the bottom of perovskite film,which could act as a barrier to prevent moisture from further eroding internal perovskites.The optimized 2D PVSCs remained 90%of the PCE after being exposed in air(50%–60%humidity,room temperature)with a continuous illumination for 300 h.

Electrical transport and current properties of rare-earth dysprosium Schottky electrode on p-type GaN at various annealing temperatures

The electrical and current transport properties of rapidly annealed Dy/p-GaN SBD are probed by I-V and C-V techniques. The estimated barrier heights（BH） of as-deposited and 200 ℃ annealed SBDs are 0.80 eV（I-V）/0.93 eV（C-V） and 0.87 eV（I-V）/1.03 eV（C-V）. However, the BH rises to 0.99 eV（I-V）/1.18 eV（C-V）and then slightly deceases to 0.92 eV（I-V）/1.03 eV（C-V） after annealing at 300 ℃ and 400 ℃. The utmost BH is attained after annealing at 300 ℃ and thus the optimum annealing for SBD is 300 ℃. By applying Cheung＇s functions, the series resistance of the SBD is estimated. The BHs estimated by I-V, Cheung＇s and ΨS-V plot are closely matched; hence the techniques used here are consistency and validity. The interface state density of the as-deposited and annealed contacts are calculated and we found that the NSS decreases up to 300 ℃ annealing and then slightly increases after annealing at 400 ℃. Analysis indicates that ohmic and space charge limited conduction mechanisms are found at low and higher voltages in forward-bias irrespective of annealing temperatures. Our experimental results demonstrate that the Poole-Frenkel emission is leading under the reverse bias of Dy/p-GaN SBD at all annealing temperatures.

Pure aromatic hydrocarbons with meta-linked phenyl-core and perihedral fluorene substitutions with/without inert groups of tert-butyl： bipolar hosts for blue phosphorescence

Two pure hydrocarbon molecules of l,3,5-tris(9-phenyl-9H-fluoren-9-yl)benzene(mTPFB)and l,3,5-tris(2-tert-butyl-9-phenyl-9H-fluoren-9-yl)benzene(tBu-mTPFB)were synthesized.Due to the conjugation blocked connection mode and rigid/bulky substitutions,these two materials possess high triplet energy,enabling them as good hosts for blue phosphor in PhOLEDs.By studying their thermal,electrochemical,electronic absorption and photoluminescent properties,it was found that the influence of the inert tert-butyl group on material photoelectrical properties is negligible.For instance,mTPFB and tBu-mTPFB showed very similar absorption and emission profiles,with almost the same bandgap,triplet energy and energy levels.However,the encapsulation of tert-butyl on the 2-position of 9-phenylfluorene enhanced material thermal stability.Most importantly,carrier transport properties were improved dramatically,as proved by the mono carrier device.Blue phosphorescent OLEDs hosted by tBu-mTPFB showed external quantum efficiency of 15.2%and current efficiency of 23.0 cd/A,which were much higher than that of the OLEDs based on mTPFB with the analogous structure.