In the past few years, the remarkable energy conversion efficiency of lead-halide-based perovskite solar cells (PSCs) has drawn extraordinary attention. However, some exposed problems in PSCs such as the low chemical stability and so forth are tough to eliminate. A fundamental understanding of ionic transport at the nanoscale is essential for developing high-performance PSCs based on the anomalous hysteresis current–voltage (I–V) curves and the poor stability. Our work is to understand the ionic transport mechanism by introducing suitable halogen substitution with insignificant impact on light absorption to hinder ion diffusion and thereby to seek a method to improve the stability. Herein, we used first-principles density functional theory (DFT) to calculate the band gaps and the optical absorption coefficients, and the interstitial and the vacancy defect diffusion barriers of halide in the orthogonal phase MAPbX3 (MA = CH3NH3, X = I, Br, I0.5Br0.5) perovskite, respectively. The research results show that a half bromine substitution not only prevents ion migration in perovskite, but also maintains a favorable light absorption capacity. It may be helpful to maintain the PSC’s property of light absorption with a similar atomic substitution. Furthermore, smaller atomic substitution for the halogen atoms may be essential for increasing the diffusion barrier.

A series of metal-free organic donor−acceptor (D−A) derivatives (ME01−ME06) of the known dye C281 were designed using first-principles calculations in order to evaluate their potential for applications in dye-sensitized solar cells (DSSCs). Their physical and electronic properties were calculated using density functional theory (DFT) and timedependent density functional theory (TD-DFT). These include molecular properties that are required to assess the feasibility of a dye to function in DSSCs: UV−vis absorption spectra, lightharvesting efficiency (LHE), and driving forces of electron injection (ΔG inj ). ME01, ME02, and ME04 are predicted to exhibit broad absorption optical spectra that cover the entire visible range, rendering these three dyes promising DSSC prospects. Device-relevant calculations on these three shortlisted dyes and the parent dye C281 were then performed, whereupon the dye molecules were adsorbed onto anatase TiO 2 surfaces to form the DSSC working electrode. Associated DSSC device characteristics of this dye•••TiO 2 interfacial structure were determined. These include the light-harvesting efficiency, the number of injected electrons, the electron-injection lifetime, and the quantum-energy alignment of the adsorbed dye molecule to that of its device components. In turn, these calculated parameters enabled the derivation of the DSSC device performance parameters: short-circuit current density, J SC , incident photon-to-electron conversion efficiency, IPCE, and open-circuit voltage, V OC . Thus, we demonstrate a systematic ab initio approach to screen rationally designed D−A dyes with respect to their potential applicability in high-performance DSSC devices.

We study Rydberg atoms modulated by strong radio-frequency (RF) fields with a frequency of 70 MHz. The Rydberg atoms are prepared in a room temperature cesium cell, and their level structure is probed using electromagnetically induced transparency (EIT). As the RF field increases from the weak-into the strong-field regime, the range of observed RF-induced phenomena progresses from AC level shifts through increasingly pronounced and numerous RF-modulation sidebands to complex state-mixing and level-crossings with high-l hydrogen-like states. Weak anharmonic admixtures in the RF field generate clearly visible modifications in the Rydberg-EIT spectra. A Floquet analysis is employed to model the Rydberg spectra, and good agreement with the experimental observations is found. Our results show that all-optical spectroscopy of Rydberg atoms in vapor cells can serve as an antenna-free, atom-based and calibration-free technique to measure and map RF electric fields and to analyze their higher-harmonic contents.

We screen a series of π-conjugated bridge groups and design a range of metal-free organic donor−π−acceptor (D−π−A) SPL101−SPL108 dyes based on the experimentally synthesized C217 dye for highly efficient dye-sensitized solar cells (DSSC) using density functional theory (DFT) and time-dependent DFT (TDDFT), and further calculate their physical and electronic properties, including geometrical structures, electronic cloud distribution, molecular orbital energy levels, absorption spectra, light harvesting efficiency (LHE), driving force of injection (ΔG inj ) and regeneration (ΔG reg ), and electron dipole moment (μ normal ). Results reveal that the π-conjugated bridge groups in SPL103 and SPL104 are promising functional groups for D−π−A organic dyes. In particular, SPL106 and SPL108 have not only smaller energy gaps, higher molar extinction coefficients, and 128 and 143 nm redshifts, but also a broader absorption spectrum covering the entire visible range up to the near-IR region of 1200 nm compared to C217 dye.