(3-Aminopropyl)trimethoxysilane Surface Passivation Improves Perovskite Solar Cell Performance by Reducing Surface Recombination Velocity

We demonstrate reduced surface recombination velocity (SRV) and enhanced power-conversion efficiency (PCE) in mixed-cation mixed-halide perovskite solar cells by using (3-aminopropyl)trimethoxysilane (APTMS) as a surface passivator. We show the APTMS serves to passivate defects at the perovskite surface, while also decoupling the perovskite from detrimental interactions at the C60 interface. We measure a SRV of ~125 + 14 cm/s, and a concomitant increase of ~100 meV in quasi-Fermi level splitting in passivated devices compared to the controls. We use time-resolved photoluminescence and excitation-correlation photoluminescence spectroscopy to show that APTMS passivation effectively suppresses non-radiative recombination. We show that APTMS improves both the fill factor and open-circuit voltage (VOC), increasing VOC from 1.03 V for control devices to 1.09 V for APTMS-passivated devices, which leads to PCE increasing from 15.90% to 18.03%. We attribute enhanced performance to reduced defect density or suppressed nonradiative recombination and low SRV at the perovskite/transporting layers interface.Comment: 22 pages, 6 figure

Resolving Nonlinear Recombination Dynamics in Semiconductors via Ultrafast Excitation Correlation Spectroscopy: Photoluminescence versus Photocurrent Detection.

We explore the application of excitation correlation spectroscopy to detect nonlinear photophysical dynamics in two distinct semiconductor classes through time-integrated photoluminescence and photocurrent measurements. In this experiment, two variably delayed femtosecond pulses excite the semiconductor, and the time-integrated photoluminescence or photocurrent component arising from the nonlinear dynamics of the populations induced by each pulse is measured as a function of inter-pulse delay by phase-sensitive detection with a lock-in amplifier. We focus on two limiting materials systems with contrasting optical properties: a prototypical lead-halide perovskite (LHP) solar cell, in which primary photoexcitations are charge photocarriers, and a single-component organic-semiconductor diode, which features Frenkel excitons as primary photoexcitations. The photoexcitation dynamics perceived by the two detection schemes in these contrasting systems are distinct. Nonlinear-dynamic contributions in the photoluminescence detection scheme arise from contributions to radiative recombination in both materials systems, while photocurrent arises directly in the LHP but indirectly following exciton dissociation in the organic system. Consequently, the basic photophysics of the two systems are reflected differently when comparing measurements with the two detection schemes. Our results indicate that photoluminescence detection in the LHP system provides valuable information about trap-assisted and Auger recombination processes, but that these processes are convoluted in a nontrivial way in the photocurrent response and are therefore difficult to differentiate. In contrast, the organic-semiconductor system exhibits more directly correlated responses in the nonlinear photoluminescence and photocurrent measurements, as charge carriers are secondary excitations only generated through exciton dissociation processes. We propose that bimolecular annihilation pathways mainly contribute to the generation of charge carriers in single-component organic semiconductor devices. Overall, our work highlights the utility of excitation correlation spectroscopy in modern semiconductor materials research, particularly in the analysis of nonlinear photophysical processes, which are deterministic for their electronic and optical properties

Ethylenediamine addition improves performance and suppresses phase instabilities in mixed-halide perovskites

We show that adding ethylenediamine (EDA) to perovskite precursor solutions improves the photovoltaic device performance and material stability of high-bromide-content, methylammonium-free, formamidinium cesium lead halide perovskites FA1–xCsxPb(I1–yBry)3, which are currently of interest for perovskite-on-Si tandem solar cells. Using spectroscopy and hyperspectral microscopy, we show that the additive improves film homogeneity and suppresses the phase instability that is ubiquitous in high-Br perovskite formulations, producing films that remain stable for over 100 days in ambient conditions. With the addition of 1 mol % EDA, we demonstrate 1.69 eV-gap perovskite single-junction p-i-n devices with a VOC of 1.22 V and a champion maximum-power-point-tracked power conversion efficiency of 18.8%, comparable to the best reported methylammonium-free perovskites. Using nuclear magnetic resonance (NMR) spectroscopy and X-ray diffraction techniques, we show that EDA reacts with FA+ in solution, rapidly and quantitatively forming imidazolinium cations. It is the presence of imidazolinium during crystallization which drives the improved perovskite thin-film properties

Architecture Optimization Dramatically Improves Reverse Bias Stability in Perovskite Solar Cells: A Role of Polymer Hole Transport Layers

We report that device architecture engineering has a substantial impact on the reverse bias instability that has been reported as a critical issue in commercializing perovskite solar cells. We demonstrate breakdown voltages exceeding -15 V in typical pin structured perovskite solar cells via two steps: i) using polymer hole transporting materials; ii) using a more electrochemically stable gold electrode. While device degradation can be exacerbated by higher reverse bias and prolonged exposure, our as-fabricated perovskite solar cells completely recover their performance even after stressing at -7 V for 9 hours both in the dark and under partial illumination. Following these observations, we systematically discuss and compare the reverse bias driven degradation pathways in perovskite solar cells with different device architectures. Our model highlights the role of electrochemical reaction rates and species in dictating the reverse bias stability of perovskite solar cells

Naphthalene-imide Self-assembled Monolayers as a Surface Modification of ITO for Improved Thermal Stability of Perovskite Solar Cells [Dataset]

38 pages. -- 1. Thermal Properties. -- 2. Cyclic Voltammetry. -- 3. Optical Characterization. -- 4. Energy Level Diagram. -- 5. Self-Assembly. -- 6. Water Contact Angle Measurements. -- 7. XPS Measurements. -- 8. Perovskite Solar Cells. -- 9. Surface Recombination Velocity Measurements. -- 10. Drift-Diffusion Simulations. -- 11. Shelf-Life Stability. -- 12. Synthesis. -- 12.1. Naphthalene monoimides 2a-2d. -- 12.2. Naphthalene diimides 3a-3d. -- 13. ReferencesElectron-transport-layer-free (ETL-free) perovskite solar cells (PSCs) show great promise for commercialization due to their simple design and ease of fabrication. However, the interface between the transparent conductive oxides such as indium-doped tin oxide (ITO) and the perovskite is not optimal due to differences in their work functions, surface defects, and wettability of the substrates. Surface modification of ITO through self-assembled monolayers (SAMs) to get ITO/SAM charge selective layers has shown great improvement in device performance in recent years, but little emphasis has been put on the stability of these devices. Here, we address this gap by introducing a series of newly synthesized naphthalene-imide derivatives which self-assemble at the interface between ITO and the perovskite interface and study their impact on the thermal stability of triple-cation PSCs. The chemical and thermal stabilities of the naphthalene-imide SAMs help improve the thermal stability of the devices, reaching T80 lifetimes exceeding 800 h for devices containing a pyridine-functionalized naphthalene diimide carboxylic acid at 85 °C in air. In addition, all SAMs improve the stabilized power output of the devices with respect to ITO-only reference devices. Drift-diffusion simulations reveal the strong influence of the ITO work function on the efficiency in ETL-free devices, and a work function reduction of 0.2 eV could improve efficiencies by over 30%. The functional diversity of naphthalene imides coupled with the ease of SAM deposition opens a pathway for stable, high-performing PSCs based on electron selective monolayers.Peer reviewe

MAPbBr3 First‐Order Distributed Feedback Laser with High Stability

A green‐emitting perovskite first‐order distributed feedback (DFB) laser based on the methylammonium lead bromide (MAPbBr3) with high stability is demonstrated for the first time. The laser achieves stable lasing at 550 nm with a full width at half maximum of 0.4 nm. Low lasing threshold of 60 μJ cm−2 under nanosecond pulsed excitation and 3.1 μJ cm−2 under femtosecond pulsed excitation is observed, showing a much lower lasing threshold compared with the second‐order DFB cavities, which are fabricated on the same substrate. By optimizing the antisolvent treatment and encapsulating with poly(methyl methacrylate), the laser lifetime, resistance to moisture, lasing threshold, and intensity are significantly improved. The lasers are fabricated with a complementary metal‐oxide‐semiconductor‐compatible process, thus offer promising potential for the integrated photonic devices

Differential responses of Lasiopodomys mandarinus and Lasiopodomys brandtii to chronic hypoxia: a cross-species brain transcriptome analysis

Abstract Background Subterranean rodents have evolved many features to adapt to their hypoxic environment. The brain is an organ that is particularly vulnerable to damage caused by exposure to hypoxic conditions. To investigate the mechanisms of adaption to a hypoxic underground environment, we carried out a cross-species brain transcriptome analysis by RNA sequencing and identified genes that are differentially expressed between the subterranean vole Lasiopodomys mandarinus and the closely related above-ground species Lasiopodomys brandtii under chronic hypoxia [10.0% oxygen (O2)] and normoxia (20.9% O2). Results A total of 355 million clean reads were obtained, including 69,611 unigenes in L. mandarinus and 69,360 in L. brandtii. A total of 235 and 92 differentially expressed genes (DEGs) were identified by comparing the hypoxic and control groups of L. mandarinus and L. brandtii, respectively. A Gene Ontology (GO) analysis showed that upregulated DEGs in both species had similar functions in response to hypoxia, whereas downregulated DEGs in L. mandarinus were enriched GO terms related to enzymes involved in aerobic reactions. In the Kyoto Encyclopedia of Genes and Genomes pathway analysis, upregulated DEGs in L. mandarinus were associated with angiogenesis and the increased O2 transport capacity of red blood cells, whereas downregulated DEGs were associated with immune responses. On the other hand, upregulated DEGs in L. brandtii were associated with cell survival, vascular endothelial cell proliferation, and neuroprotection, while downregulated genes were related to the synaptic transmission by neurons. Conclusions L. mandarinus actively adapts its physiological functions to hypoxic conditions, for instance by increasing O2 transport capacity and modulating O2 consumption. In contrast, L. brandtii reacts passively to hypoxia by decreasing overall activity in order to reduce O2 consumption. These results provide insight into hypoxia adaptation mechanisms in subterranean rodents that may be applicable to humans living at high altitudes or operating in other O2-poor environments

Studying Hydrogen–Halide Interactions in Lead Halide Perovskite with Isoelectronic Cations

A-site cations in lead halide perovskite (LHP) can significantly impact the optoelectronic device efficiency and stability. These efficiency impacts have not been correlated to cation structural features because it is difficult to isolate the independent contributions from the sizes of these A-site cations and hydrogen–halide interaction between the A-site cations and PbX6 octahedra. To address this, we designed two isoelectronic cationic ligands (guanidinium and uronium) that are nearly identical in size but have different numbers of N–H moieties that can interact with PbX6 octahedra and studied their differences in passivating LHP solar cell interfaces. While the solar cells showed little improvement after being treated by the alkylated uronium ligand, the alkylated guanidinium ligand increased both the fill factor (from 72.4% to ∼80%) and power conversion efficiency (from 15.4% to 17.7%) compared to the untreated device, along with an increased hysteresis index (from 0.02 to 0.12). While the guanidinium-based ligand or uronium-based ligand does not have significant impacts on the morphology of the LHP, the guanidinium-based ligand demonstrated a much more pronounced effect on surface passivation of the (Cs0.17FA0.83)Pb(I0.75Br0.25)3 films (FA = formamidinium). NMR and XRD data together suggested the guanidinium-based ligand interacts with the (Cs0.17FA0.83)Pb(I0.75Br0.25)3 and the CsPbI3 lattice with 5 H–X interactions, while the uronium-based ligand interacts with 4 due to the different lattice sizes. Raman spectra indicate that the H–X interaction between the cations and the PbX6 octahedra alters the electron distribution of the resulting materials. By using a pair of isoelectronic organic cations, we excluded other variables and demonstrated the importance of the hydrogen–halide interactions between cations and PbX6 octahedra on the surface passivation and optoelectronic properties of the LHP materials

Mulberry (Morus atropurpurea Roxb.) leaf protein hydrolysates ameliorate dextran sodium sulfate-induced colitis via integrated modulation of gut microbiota and immunity

The molecular action underlying peptide intervention before and after colitis induction is different. To investigate the alleviated effects of mulberry leaf protein hydrolysates (MLPH) on colitis and its potential mechanism, MLPH was administered to colitis mice. Results showed that MLPH efficiently alleviated the colitis, and the preventive and therapeutic (P&T) intervention was more effective than the therapeutic intervention alone. MLPH significantly decreased pro-inflammatory cytokines, improved histological damage, and increased SCFA contents. MLPH also reversed microbiota dysbiosis. The dominant genera in MLPH intervention group were significantly positively correlated with colitis prevention parameters (p < 0.01). The DSS group was the opposite. In addition, the dominant genera of MLPH intervention group showed a co-occurrence relationship with each other. Overall, MLPH could alleviate colitis by integrated modulation of gut microbiota and inflammation response. MLPH may be a promising dietary approach for sustaining gut health to lower the risk of developing colitis