19 research outputs found
Inducing Charge Separation in Solid-State Two-Dimensional Hybrid Perovskites through the Incorporation of Organic Charge-Transfer Complexes
No full textTwo-dimensional (2D) hybrid perovskites make up an emerging class of materials for optoelectronic applications in which inorganic octahedral layers are separated by nonconductive large organic cations. This leads to a high-dimensional and dielectric confinement and hence a high exciton binding energy, which severely limits their application in devices in which charge carrier separation is required. In this work, we achieve improved charge separation by replacing nonconductive organic cations with organic charge-transfer complexes consisting of a pyrene donor and a tetracyanoquinodimethane acceptor. Steady-state absorption measurements show that these materials exhibit optical features that match with the absorption of the organic charge-transfer complexes. Using microwave conductivity and femtosecond transient absorption, we show that photoexcitation of these charge-transfer states leads to long-lived mobile charges in the inorganic layers. While the efficiency of charge separation is relatively low, these experiments demonstrate that it is possible to induce charge separation in solid-state 2D perovskites by engineering the organic layer.ChemE/Opto-electronic Material
2D layered perovskite containing functionalised benzothieno-benzothiophene molecules: Formation, degradation, optical properties and photoconductivity
No full text2D layered hybrid perovskites are currently in the spotlight for applications such as solar cells, light-emitting diodes, transistors and photodetectors. The structural freedom of 2D layered perovskites allows for the incorporation of organic cations that can potentially possess properties contributing to the performance of the hybrid as a whole. In this study, we incorporated a benzothieno[3,2-b]benzothiophene (BTBT) alkylammonium cation into the organic layer of a 2D layered lead iodide perovskite. The formation and degradation of this material are discussed in detail. It is shown that the use of a solvent vapour annealing method significantly enhances the absorption, emission and crystallinity of films of this 2D layered perovskite as compared to regular thermal annealing. The photoconductivity of the films was determined using time-resolved microwave conductivity (TRMC) as well as in a device. In both cases, the solvent vapour annealed films show markedly higher photoconductivity than the films obtained using the regular thermal annealing approach.ChemE/Opto-electronic Material
Tin-lead-metal halide perovskite solar cells with enhanced crystallinity and efficiency by addition of fluorinated long organic cation
No full textHighly performing mixed Sn/Pb-metal halide perovskite solar cells (PSCs) are among the most promising options to reduce Pb content in perovskite devices and enable, owing to their reduced bandgap, the fabrication of all-perovskite tandem solar cells. Whereas pure-Pb perovskite devices exhibit efficiency up to 25.5%, alongside a high open-circuit voltage (≈1.2 V), Sn-Pb PSCs still show lower performances (22.2%) due to higher open-circuit voltage losses. Here, we introduced 2,3,4,5,6-pentafluorophenethylammonium cations in a perovskite active layer of composition (FASnI3)0.5(MAPbI3)0.5 to obtain highly oriented films with improved thermal stability. The treated films exhibit merged grains with no evidence of 2D structures, which could help to reduce the trap state density at the surface and grain boundaries. Solar cells fabricated with the fluorinated cation added to the active layer displayed reduced trap-assisted recombination losses and lower background carrier density, which leads to enhanced open-circuit voltages with respect to the reference samples and the active layers incorporating unfluorinated phenethylammonium cations. The best device reached an efficiency of 19.13%, with an open-circuit voltage of 0.84 V, which is substantially improved with respect to the reference sample showing 17.47% efficiency and 0.77 V open-circuit voltage. More importantly, the fluorinated cations' addition is instrumental to improve the device's thermal stability; 90.3% of the solar cell initial efficiency is maintained after 90 min of thermal stress at 85 °C in a nitrogen atmosphere.</p
Multi-layered hybrid perovskites templated with carbazole derivatives: Optical properties, enhanced moisture stability and solar cell characteristics
No full textResearch into 2D layered hybrid perovskites is on the rise due to the enhanced stability of these materials compared to 3D hybrid perovskites. Recently, interest towards the use of functional organic cations for these materials is increasing. However, a vast amount of the parameter space remains unexplored in multi-layered (n > 1) hybrid perovskites for solar cell applications. Here, we incorporate carbazole derivatives as a proof of concept towards the use of tailored functional molecules in multi-layered perovskites. Films of low-n carbazole containing perovskites show high photoconductivity half-lifetimes. Higher-n (〈n〉 = 40) multi-layered perovskite films possess charge carrier diffusion lengths comparable to MAPI thin films. Solar cells containing these materials have comparable efficiencies to our MAPI and phenethylammonium (PEA)-containing multi-layered perovskite reference devices. Moisture stability tests were performed both at the material and device levels. In comparison to MAPI and PEA-based materials and solar cells, the addition of a small percentage of the carbazole derivative to the perovskite material significantly enhances the moisture stability.ChemE/Opto-electronic Material
Critical Roles of Ultrafast Energy Funnelling and Ultrafast Singlet-Triplet Annihilation in Quasi-2D Perovskite Optical Gain Mechanisms
No full textQuasi-2D (Q2D) perovskite possess considerable potential for light emission and amplification technologies. Recently, mixed films containing Q2D perovskite grains with varying layer thicknesses have shown great promise as carrier concentrators, effectively mitigating trap-mediated recombination. In this strategy, photo-excitations are rapidly funnelled down an energy gradient to the thickest grains, leading to amplified spontaneous emission (ASE). However, the quantum-confined Q2D slabs also stabilize the formation of unwanted triplet excitons, resulting in parasitic quenching of emissive singlet states. Here, a novel ultrafast photoluminescence spectroscopy is used to study photoexcitation dynamics in mixed-layer Q2D perovskites. By analysing spectra with high temporal and energy resolution, this is found that sub-picosecond energy transfer to ASE sites is accompanied by excitation losses due to triplet formation on grains with small and intermediate thicknesses. Further accumulation of triplets creates a bottleneck in the energy cascade, effectively quenching incoming singlet excitons. This ultrafast annihilation within 200 femtosecond outpaces energy transfer to ASE sites, preventing the build-up of population inversion. This study highlights the significance of investigating photoexcitation dynamics on ultrafast timescales, encompassing lasing dynamics, energy transfer, and singlet-triplet annihilation, to gain crucial insights into the photophysics of the optical gain process in Q2D perovskites.I.W. and K.C. acknowledge support from the Marsden Fund (17-VUW-154 and MFP-VUW2307), Royal Society of New Zealand. W.T.M.V.G.,L.L., P.G. and D.V. acknowledge the FWO for the funding of the SBOproject PROCEED (FWOS002019N) and the senior FWO research projectG043320N. P.G. acknowledges funding from FWO Vlaanderen through Re-search projects INTRIQATE (G0C5723N) & HITEC (G037221N). R.E. ac-knowledges the FWO for the funding of his personal FWO-SB Ph.D. fel-lowship (1SB3725N
Surface Modulation via Conjugated Bithiophene Ammonium Salt for Efficient Inverted Perovskite Solar Cells
No full textThe metal halide perovskite absorbers are prone to surface defects, which severely limit the power conversion efficiencies (PCEs) and the operational stability of the perovskite solar cells (PSCs). Herein, trace amounts of bithiophene propylammonium iodide (bi-TPAI) are applied to modulate the surface properties of the gas-quenched perovskite. It is found that the bi-TPAI surface treatment has negligible impact on the perovskite morphology, but it can induce a defect passivation effect and facilitate the charge carrier extraction, contributing to the gain in the open-circuit voltage (Voc) and fill factor. As a result, the PCE of the gas-quenched sputtered NiOx-based inverted PSCs is enhanced from the initial 20.0% to 22.0%. Most importantly, the bi-TPAI treatment can largely alleviate or even eliminate the burn-in process during the maximum power point tracking measurement, improving the operational stability of the devices
3D Perovskite Passivation with a Benzotriazole-Based 2D Interlayer for High-Efficiency Solar Cells
No full text2H-Benzotriazol-2-ylethylammonium bromide and iodide and its difluorinated derivatives are synthesized and employed as interlayers for passivation of formamidinium lead triiodide (FAPbI3) solar cells. In combination with PbI2 and PbBr2, these benzotriazole derivatives form two-dimensional (2D) Ruddlesden-Popper perovskites (RPPs) as evidenced by their crystal structures and thin film characteristics. When used to passivate n-i-p FAPbI3 solar cells, the power conversion efficiency improves from 20% to close to 22% by enhancing the open-circuit voltage. Quasi-Fermi level splitting experiments and scanning electron microscopy cathodoluminescence hyperspectral imaging reveal that passivation provides a reduced nonradiative recombination at the interface between the perovskite and hole transport layer. Photoluminescence spectroscopy, angle-resolved grazing-incidence wide-angle X-ray scattering, and depth profiling X-ray photoelectron spectroscopy studies of the 2D/three-dimensional (3D) interface between the benzotriazole RPP and FAPbI3 show that a nonuniform layer of 2D perovskites is enough to passivate defects, enhance charge extraction, and decrease nonradiative recombination
Quasi-2D Hybrid Perovskite Formation Using Benzothieno[3,2-b]Benzothiophene (BTBT) Ammonium Cations: Substantial Cesium Lead(II) Iodide Black Phase Stabilization
No full text3D hybrid perovskites (APbX3) have made a significant impact on the field of optoelectronic materials due to their excellent performance combined with facile solution deposition and up-scalable device fabrication. Nonetheless, these materials suffer from environmental instability. To increase material stability, the organic cation (A) is substituted by the non-volatile cesium cation. However, the desired photoactive cesium lead(II) iodide black phase is metastable in ambient conditions and spontaneously converts into the photo-inactive yellow δ-phase. In this work, the black phase is stabilized by the formation of a quasi-2D perovskite containing a benzothieno[3,2-b]benzothiophene (BTBT) large organic ammonium cation. Thermal analysis shows that degradation of the butylammonium (BA)-based quasi-2D perovskite (BA)2CsPb2I7 sets in at ≈130 °C, while (BTBT)2CsPb2I7 is phase-stable until ≈230 °C. Additionally, the (BTBT)2CsPb2I7 film does not show any sign of degradation after exposure to 77% Relative Humidity in the dark for 152 days, while (BA)2CsPb2I7 degrades in a single day. Photoconductor-type detectors based on (BTBT)2CsPb2I7 demonstrate an increased external quantum efficiency and a similar specific detectivity compared to the BA-based reference detectors. The results demonstrate the utility of employing a BTBT cation within the organic layer of quasi-2D perovskites to significantly enhance the stability while maintaining the optoelectronic performance.Green Open Access added to TU Delft Institutional Repository 'You share, we take care!' - Taverne project https://www.openaccess.nl/en/you-share-we-take-care Otherwise as indicated in the copyright section: the publisher is the copyright holder of this work and the author uses the Dutch legislation to make this work public.ChemE/Opto-electronic Material
Functionalization of 2D layered hybrid perovskites with benzotriazole- based organic ammonium cations for solar cell applications
No full textLow-dimensional hybrid perovskites containing an organic cation with an extended conjugated system: Tuning the excitonic absorption features
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