Co-Cation Engineering via Mixing of Acetamidinium and Rubidium in FASnI for Tin Perovskite Solar Cells to Attain 14.5% Efficiency.

Tin perovskite solar cells (TPSCs) were developed by adding the co-cations acetamidinium (AC) and rubidium (Rb) in varied proportions based on the FASnI structure (E1). We found that adding 10% AC and 3% Rb can optimize the device (E1AC10Rb3) to attain an efficiency of power conversion of 14.5% with great shelf- and light-soaking stability.

Dual-plasmonic Au@CuS yolk@shell nanocrystals for photocatalytic hydrogen production across visible to near infrared spectral region.

Near infrared energy remains untapped toward the maneuvering of entire solar spectrum harvesting for fulfilling the nuts and bolts of solar hydrogen production. We report the use of Au@CuS yolk@shell nanocrystals as dual-plasmonic photocatalysts to achieve remarkable hydrogen production under visible and near infrared illumination. Ultrafast spectroscopic data reveal the prevalence of long-lived charge separation states for Au@CuS under both visible and near infrared excitation.

Highly Efficient HTM-Free Tin Perovskite Solar Cells with Outstanding Stability Exceeding 10000 h.

The bottleneck in the rapid development of tin-based perovskite solar cells (TPSCs) is the inherent chemical instability. Although this is being addressed continuously, the device performance has not improved further due to the use of PEDOT:PSS as the hole-transport material (HTM), which has poor long-term stability. Herein we have applied commercial ITO nanoparticles over ITO glass substrates and altered the surface chemistry of the ITO electrode via a simple two-step thermal annealing, followed by a UV-ozone treatment.

Effect of Acidic Strength of Surface Ligands on the Carrier Relaxation Dynamics of Hybrid Perovskite Nanocrystals.

Perovskite nanocrystals (PeNCs) are known for their use in numerous optoelectronic applications. Surface ligands are critical for passivating surface defects to enhance the charge transport and photoluminescence quantum yields of the PeNCs. Herein, we investigated the dual functional abilities of bulky cyclic organic ammonium cations as surface-passivating agents and charge scavengers to overcome the lability and insulating nature of conventional long-chain type oleyl amine and oleic acid ligands.

Energy and Charge Transfer Dynamics in Red-Emitting Hybrid Organo-Inorganic Mixed Halide Perovskite Nanocrystals.

We report time-resolved spectral properties of highly stable and efficient red-emitting hybrid perovskite nanocrystals with the composition FAMAPbBrI (FAMA PeNC) synthesized by using the hot-addition method. The PL spectrum of the FAMA PeNC shows a broad asymmetric band covering 580 to 760 nm with a peak at 690 nm which can be deconvoluted into two bands corresponding to the MA and FA domains. The interactions between the MA and FA domains are shown to affect the relaxation dynamics of the PeNCs from the subpicosecond to tens of nanoseconds scale.

Retarded Charge Recombination to Enhance Photocatalytic Performance for Water-Free CO Reduction Using Perovskite Nanocrystals as Photocatalysts.

Femtosecond transient absorption spectral (TAS) investigations were performed to understand the carrier relaxation mechanism for perovskite nanocrystals CsFAPbBr (CF, = 0.45) and CsPbBr (CS), which served as efficient photocatalysts for splitting of CO into CO and O in the absence of water. Upon light irradiation for 12 h, formation of deep trap states was found for both CS and CF samples with spectral characteristics of the TAS photobleach (PB) band showing a long spectral tail extending to the long wavelength region.

Interface-Enhanced Charge Recombination in the Heterojunction between Perovskite Nanocrystals and BiOI Nanosheets Serves as an S-Scheme Photocatalyst for CO Reduction.

We designed an S-heterojunction system with a perovskite nanocrystal, CsFAPbBr (CF), coupled with a bismuth oxyiodide (BiOI) nanosheet to form a perovskite heterojunction (PHJ) photocatalyst. On the basis of femtosecond transient absorption measurements, the pristine CF sample has two charge recombination periods, 100 and 900 ps, corresponding to surface and bulk trap-state relaxations, respectively. When CF was in contact with BiOI to form an S-heterojunction, rapid interfacial charge recombination occurred to show two decay components with time coefficients 1 and 35 ps, responsible for the electron-hole recombination in the surface and bulk states, respectively.

Femtosecond Exciton and Carrier Relaxation Dynamics of Two-Dimensional (2D) and Quasi-2D Tin Perovskites.

The dynamics of exciton and free-carrier relaxation of low-dimensional tin iodide perovskites, BAFASnI, where = 1 (N1), 2 (N2), 5 (N5), and 10 (N10), were investigated with femtosecond transient absorption spectra (TAS). The absorption and photoluminescence spectra of N1 and N2 show exciton characteristics due to quantum confinement, whereas N5 and N10 display a free-carrier nature, the same as for bulk three-dimensional (3D) films. The TAS profiles were fitted according to a global kinetic model with three time coefficients representing the interactions of biexcitons, trions, and excitons for N1 and N2 and hot carriers, cold carriers, and shallow trap carriers for N5 and N10.

Mixing of Azetidinium in Formamidinium Tin Triiodide Perovskite Solar Cells for Enhanced Photovoltaic Performance and High Stability in Air.

Overcoming the issue of the stability of tin-based perovskites is a major challenge for the commercial development of lead-free perovskite solar cells. To attack this problem, a new organic cation, azetidinium (AZ), is incorporated into the crystal structure of formamidinium tin triiodide (FASnI ) to form the mixed-cation perovskite AZ FA SnI . As AZ has a similar size to FA but a larger dipole moment, hybrid AZ FA SnI films exhibit variation in optical and electronic properties on increasing the proportion of AZ.

Femtosecond Transient Absorption Spectra and Dynamics of Carrier Relaxation of Tin Perovskites in the Absence and Presence of Additives.

The effects of additives SnF (10%) and EDAI (1%) on the dynamics of carrier relaxation of formamidinium tin triiodide (FASnI) perovskite were studied using femtosecond transient absorption spectra (TAS) with excitation at 600 and 870 nm. The TAS were analyzed according to a parallel sequential kinetic model with a global fit through singular-value decomposition. For excitation at 600 nm, two relaxation paths were found: one involved hot and cold carriers in the bulk state undergoing shallow bulk-defect-mediated charge recombination; the other involved trap carriers in the surface state undergoing deep surface-defect-mediated charge recombination.

Development of Hybrid Pseudohalide Tin Perovskites for Highly Stable Carbon-Electrode Solar Cells.

Tin-based perovskites degrade rapidly upon interaction with water and oxygen in air because Sn-I bonds are weak. To address this issue, we developed novel tin perovskites, FASnI(SCN) ( = 0, 1, 2, or 3), by employing a pseudohalide, thiocyanate (SCN), as a replacement for halides and as an inhibitor to suppress the Sn/Sn oxidation. The structural and electronic properties of pseudohalide tin perovskites in this series were explored with quantum-chemical calculations by employing the plane-wave density functional theory (DFT) method; the corresponding results are consistent with the experimental results.

Interfacial Investigation on Printable Carbon-Based Mesoscopic Perovskite Solar Cells with NiO/C Back Electrode.

Solar cells with high efficiency, low cost, and high stability are the target for the new generation of solar cells. A fully printable perovskite (CHNHPbI) solar cell (PSC) with device architecture FTO/TiO/AlO/NiO/C is fabricated in the current research as a low-cost and relatively stable structure and is investigated to determine how different fabrication factors such as the thickness of the insulating spacer layer (AlO) or treatments such as heat and UV-O treatments can affect the interfacial properties of this multilayer mesoporous structure. X-ray photoelectron spectra (XPS) show that UV-O treatment increases the Ni(NiO) phase on the surface of the black nickel oxide layer leading to better charge extraction and increasing open-circuit voltage (V) up to 0.

Cobalt Oxide (CoO) as an Efficient Hole-Extracting Layer for High-Performance Inverted Planar Perovskite Solar Cells.

CoO is a promising hole-extracting layer (HEL) for inverted planar perovskite solar cells with device configuration ITO/CoO/CHNHPbI/PCBM/Ag. The devices fabricated according to a simple solution procedure showed the best photovoltaic performance attaining power conversion efficiency (PCE) of 14.5% under AM 1.

Simultaneous Observation of an Intraband Transition and Distinct Transient Species in the Infrared Region for Perovskite Solar Cells.

Solar cells based on organometal-halide perovskites such as CH3NH3PbI3 have emerged as a promising next-generation photovoltaic system, but the underlying photophysics and photochemistry remain to be established because of the limited availability of methods to implement the simultaneous and direct measurement of various charge carriers and ions that play a crucial role in the operating device. We used nanosecond time-resolved infrared (IR) spectroscopy to investigate, with high molecular specificity, distinct transient species that are formed in perovskite solar cells after photoexcitation. In CH3NH3PbI3 planar-heterojuction solar cells, we simultaneously observed infrared spectral signatures that are associated with an intraband transition of conduction-band electrons, Fano resonance, and the spiro-OMeTAD cation having an exceptionally short lifetime of 1.

Direct observation of the solvent effects on the low-lying nπ* and ππ* excited triplet states of acetophenone derivatives in thermal equilibrium.

Low-lying excited triplet states of aromatic carbonyl compounds exhibit diverse photophysical and photochemical properties of fundamental importance. Despite tremendous effort in studying those triplet states, the effects of substituents and solvents on the energetics of the triplet manifold and on photoreactivity remain to be fully understood. We have recently studied the ordering of the low-lying nπ* and ππ* excited triplet states and its substituent dependence in acetophenone derivatives using nanosecond time-resolved near-IR (NIR) spectroscopy.

Mechanism of back electron transfer in an intermolecular photoinduced electron transfer reaction: solvent as a charge mediator.

Back electron transfer (BET) is one of the important processes that govern the decay of generated ion pairs in intermolecular photoinduced electron transfer reactions. Unfortunately, a detailed mechanism of BET reactions remains largely unknown in spite of their importance for the development of molecular photovoltaic structures. Here, we examine the BET reaction of pyrene (Py) and 1,4-dicyanobenzene (DCB) in acetonitrile (ACN) by using time-resolved near- and mid-IR spectroscopy.

Is our way of thinking about excited states correct? Time-resolved dispersive IR study on p-nitroaniline.

Low-lying excited electronic states of an important class of molecules known as push-pull chromophores are central to understanding their potential nonlinear optical properties. Here we report that a combination of high-sensitivity nanosecond time-resolved dispersive IR spectroscopy and DFT calculations on p-nitroaniline (PNA), a prototypical push-pull molecule, reveals that PNA in the lowest excited triplet state has a partial quinoid structure. In this structure, the quinoid configuration is restricted to a part of the phenyl ring adjacent to the NO(2) group.