CD98hc facilitates B cell proliferation and adaptive humoral immunity.

The proliferation of antigen-specific lymphocytes and resulting clonal expansion are essential for adaptive immunity. We report here that B cell-specific deletion of the heavy chain of CD98 (CD98hc) resulted in lower antibody responses due to total suppression of B cell proliferation and subsequent plasma cell formation. Deletion of CD98hc did not impair early B cell activation but did inhibit later activation of the mitogen-activated protein kinase Erk1/2 and downregulation of the cell cycle inhibitor p27. Reconstitution of CD98hc-deficient B cells with CD98hc mutants showed that the integrin-binding domain of CD98hc was required for B cell proliferation but that the amino acid-transport function of CD98hc was dispensable for this. Thus, CD98hc supports integrin-dependent rapid proliferation of B cells. We propose that the advantage of adaptive immunity favored the appearance of CD98hc in vertebrates

Phase segregation in mixed-halide perovskites affects charge-carrier dynamics while preserving mobility

Mixed halide perovskites can provide optimal bandgaps for tandem solar cells which are key to improved cost-efficiencies, but can still suffer from detrimental illumination-induced phase segregation. Here we employ optical-pump terahertz-probe spectroscopy to investigate the impact of halide segregation on the charge-carrier dynamics and transport properties of mixed halide perovskite films. We reveal that, surprisingly, halide segregation results in negligible impact to the THz charge-carrier mobilities, and that charge carriers within the I-rich phase are not strongly localised. We further demonstrate enhanced lattice anharmonicity in the segregated I-rich domains, which is likely to support ionic migration. These phonon anharmonicity effects also serve as evidence of a remarkably fast, picosecond charge funnelling into the narrow-bandgap I-rich domains. Our analysis demonstrates how minimal structural transformations during phase segregation have a dramatic effect on the charge-carrier dynamics as a result of charge funnelling. We suggest that because such enhanced recombination is radiative, performance losses may be mitigated by deployment of careful light management strategies in solar cells

Excellent long-range charge-carrier mobility in 2D perovskites

The use of layered, 2D perovskites can improve the stability of metal halide perovskite thin films and devices. However, the charge carrier transport properties in layered perovskites are still not fully understood. Here, the sum of the electron and hole mobilities (Σμ) in thin films of the 2D perovskite PEA2PbI4, through transient electronically contacted nanosecond-to-millisecond photoconductivity measurements, which are sensitive to long-time, long-range (micrometer length scale) transport processes is investigated. After careful analysis, accounting for both early-time recombination and the evolution of the exciton-to-free-carrier population, a long-range mobility of 8.0 +/− 0.6 cm2 (V s)–1, which is ten times greater than the long-range mobility of a comparable 3D material FA0.9Cs0.1PbI3 is determined. These values are compared to ultra-fast transient time-resolved THz photoconductivity measurements, which are sensitive to early-time, shorter-range (tens of nm length scale) mobilities. Mobilities of 8 and 45 cm2 (V s)–1 in the case of the PEA2PbI4 and FA0.9Cs0.1PbI3, respectively, are obtained. This previously unreported concurrence between the long-range and short-range mobility in a 2D material indicates that the polycrystalline thin films already have single-crystal-like qualities. Hence, their fundamental charge carrier transport properties should aid device performance

CsPbBr3 nanocrystal films: Deviations from bulk vibrational and optoelectronic properties

Metal‐halide perovskites (MHP) are highly promising semiconductors for light‐emitting and photovoltaic applications. The colloidal synthesis of nanocrystals (NCs) is an effective approach for obtaining nearly defect‐free MHP that can be processed into inks for low‐cost, high‐performance device fabrication. However, disentangling the effects of surface ligands, morphology, and boundaries on charge‐carrier transport in thin films fabricated with these high‐quality NCs is inherently difficult. To overcome this fundamental challenge, terahertz (THz) spectroscopy is employed to optically probe the photoconductivity of CsPbBr3 NC films. The vibrational and optoelectronic properties of the NCs are compared with those of the corresponding bulk polycrystalline perovskite and significant deviations are found. Charge‐carrier mobilities and recombination rates are demonstrated to vary significantly with the NC size. Such dependences derive from the localized nature of charge carriers within NCs, with local mobilities dominating over interparticle transport. It is further shown that the colloidally synthesized NCs have distinct vibrational properties with respect to the bulk perovskite, exhibiting blue‐shifted optical phonon modes with enhanced THz absorption strength that also manifest as strong modulations in the THz photoconductivity spectra. Such fundamental insights into NC versus bulk properties will guide the optimization of nanocrystalline perovskite thin films for optoelectronic applications

Heterogeneous photon recycling and charge diffusion enhance charge transport in quasi-2D lead-halide perovskite films

The addition of large hydrophobic cations to lead halide perovskites has significantly enhanced the environmental stability of photovoltaic cells based on these materials. However, the associated formation of two-dimensional structures inside the material can lead to dielectric confinement, higher exciton binding energies, wider bandgaps and limited charge-carrier mobilities. Here we show that such effects are not detrimental to the charge transport for carefully processed films comprising a self-assembled thin layer of quasi-two-dimensional (2D) perovskite interfaced with a 3D MAPbI3andnbsp;perovskite layer. We apply a combination of time-resolved photoluminescence and photoconductivity spectroscopy to reveal the charge-carrier recombination and transport through the film profile, when either the quasi-2D or the 3D layers are selectively excited. Through modeling of the recorded dynamics, we demonstrate that while the charge-carrier mobility is lower within the quasi-2D region, charge-carrier diffusion to the 3D phase leads to a rapid recovery in photoconductivity even when the quasi-2D region is initially photoexcited. In addition, the blue-shifted emission originating from quasi-2D regions overlaps significantly with the absorption spectrum of the 3D perovskite, allowing for highly effective andldquo;heterogeneous photon recyclingandrdquo;. We show that this combination fully compensates for the adverse effects of electronic confinement, yielding quasi-2D perovskites with highly efficient charge transporting properties.</p

Heterogeneous photon recycling and charge diffusion enhance charge transport in quasi-2D lead-halide perovskite films

The addition of large hydrophobic cations to lead halide perovskites has significantly enhanced the environmental stability of photovoltaic cells based on these materials. However, the associated formation of two-dimensional structures inside the material can lead to dielectric confinement, higher exciton binding energies, wider bandgaps and limited charge-carrier mobilities. Here we show that such effects are not detrimental to the charge transport for carefully processed films comprising a self-assembled thin layer of quasi-two-dimensional (2D) perovskite interfaced with a 3D MAPbI3 perovskite layer. We apply a combination of time-resolved photoluminescence and photoconductivity spectroscopy to reveal the charge-carrier recombination and transport through the film profile, when either the quasi-2D or the 3D layers are selectively excited. Through modeling of the recorded dynamics, we demonstrate that while the charge-carrier mobility is lower within the quasi-2D region, charge-carrier diffusion to the 3D phase leads to a rapid recovery in photoconductivity even when the quasi-2D region is initially photoexcited. In addition, the blue-shifted emission originating from quasi-2D regions overlaps significantly with the absorption spectrum of the 3D perovskite, allowing for highly effective “heterogeneous photon recycling”. We show that this combination fully compensates for the adverse effects of electronic confinement, yielding quasi-2D perovskites with highly efficient charge transporting properties.</p

Optoelectronic properties of mixed iodide-bromide perovskites from first-principles computational modeling and experiment

Halogen mixing in lead-halide perovskites is an effective route for tuning the band gap in light emission and multijunction solar cell applications. Here we report the effect of halogen mixing on the optoelectronic properties of lead-halide perovskites from theory and experiment. We applied the virtual crystal approximation within density functional theory, the &lt;i&gt;GW&lt;/i&gt; approximation, and the Bethe-Salpeter equation to calculate structural, vibrational, and optoelectronic properties for a series of mixed halide perovskites. We separately perform spectroscopic measurements of these properties and analyze the impact of halogen mixing on quasiparticle band gaps, effective masses, absorption coefficients, charge-carrier mobilities, and exciton binding energies. Our joint theoretical-experimental study demonstrates that iodide-bromide mixed-halide perovskites can be modeled as homovalent alloys, and local structural distortions do not play a significant role for the properties of these mixed species. Our study outlines a general theoretical-experimental framework for future investigations of novel chemically mixed systems

Charge-carrier trapping dynamics in bismuth-doped thin films of MAPbBr3 perovskite

Successful chemical doping of metal halide perovskites with small amounts of heterovalent metals has attracted recent research attention because of its potential to improve long-term material stability and tune absorption spectra. However, some additives have been observed to impact negatively on optoelectronic properties, highlighting the importance of understanding charge-carrier behavior in doped metal halide perovskites. Here, we present an investigation of charge-carrier trapping and conduction in films of MAPbBr3 perovskite chemically doped with bismuth. We find that the addition of bismuth has no effect on either the band gap or exciton binding energy of the MAPbBr3 host. However, we observe a substantial enhancement of electron-trapping defects upon bismuth doping, which results in an ultrafast charge-carrier decay component, enhanced infrared emission, and a notable decrease of charge-carrier mobility. We propose that such defects arise from the current approach to Bi-doping through addition of BiBr3, which may enhance the presence of bromide interstitials

Postpassivation of multication perovskite with rubidium butyrate

Many multication perovskites for highly stable and efficient solar cells benefit from rubidium iodide introduced in the precursor solution. It is well-known that Rb+ influences positively the optoelectronic and mobility properties and has a direct effect upon crystallization and halide homogenization. As Rb+ is often incorporated by adding RbI in the precursor solution, it can be difficult to distinguish the influence of Rb+ and I– separately. Herein, we report a postpassivation of methylammonium-free (CsFA) perovskite films with rubidium butyrate (RbBu). The passivation with RbBu increases the hydrophobicity of the perovskite surface and passivates shallow and deep traps, leading to an increase of charge-carrier lifetimes and diffusion lengths. Consequently, a better photovoltaic performance is also observed. These superior properties are attributed to both surface (halide-vacancy) and grain-boundary passivation by the carboxylate group and Rb+, respectively. We found that Rb+ itself acts as a direct and powerful passivating agent for multication perovskites, and this is proven by decoupling its contribution and halide’s contribution to other important performance parameters (e.g., crystallization, halide vacancies filling, etc.)