Vertically Oriented Perovskites with Minimized Intrinsic Boundaries for Efficient Photovoltaics.

Intrinsic boundaries formed by grain stacks of randomly oriented perovskite crystallites seriously restrict charge transport in the resultant photovoltaic devices, whereas direct passivation of these defects remains unexplored, and it is desirable to modulate perovskite growth with uniform orientation. Herein, we report a simple but effective method to regulate perovskite crystallization by employing a volatile and polymerizable monomer of hydroxyethyl methacrylate (HEMA), which can simultaneously interact with both FA+ and Pb2+ via hydrogen and coordination bonding, respectively, to seed perovskite crystallization with accelerated nucleation and retarded crystal growth. Upon thermal annealing, the gradual volatilization and partial self-condensation of the HEMA drive the perovskite growth perpendicularly to the substrate, leading to largely suppressed defect states, improved crystallinity, and a reduced Young's modulus of the perovskite film. As a result, champion efficiencies exceeding 24 and 22% with improved operational and mechanical stability of the optimized perovskite solar cells based on rigid and flexible substrates were finally achieved.

Al-Modified CuO/Cu2O for High-Temperature Thermochemical Energy Storage: from Reaction Performance to Modification Mechanism.

Next-generation concentrated solar power plants with high-temperature energy storage requirements stimulate the pursuit of advanced thermochemical energy storage materials. Copper oxide emerges as an attractive option with advantages of high energy density and low cost. But its easy sinterability limits its reversibility and cyclic stability performance. In this work, aluminum-doped copper oxides are synthesized and evaluated via thermogravimetric analysis. The reversibility of Cu-Al oxides reaches 99.5% in the first redox cycle and maintains 81.1% of the initial capacity after 120 cycles. The Al element can modify the CuO particle surface in the form of CuAl2O4, which separates the copper oxide particles from each other during redox cycles to avoid agglomeration and participates in the redox reaction. Through DFT analysis, the introduction of Al is found to increase the formation energy of copper vacancies in copper oxides, which helps avoid the sintering problem and thus improves the oxidation rate. This study provides a generalizable operational mechanism of element doping and can serve as a guideline for the optimization of high-performance materials in thermochemical energy storage.

Organic electro-optic modulator using transparent conducting oxides as electrodes.

A novel organic electro-optic (EO) modulator using transparent conducting oxides (ZnO and In2O3) as electrodes is demonstrated for the first time. The modulator employs the poled guest-host chromophore/polymer material AJL8/APC having r33=35pm/V and is able to achieve a low Vpi=2.8 V switching voltage for an 8mm-long device at a wavelength of 1.31ìm. This corresponds to a Vpi=1.1 V switching voltage for a 1cm-long device in a push-pull configuration. The push-pull VpiL figure of merit normalized for the EO coefficient is thus 1.1V-cm/(35pm/V), which is 3-4x lower than that can be achieved with a convetional modulator structure. The bottom electrode is ZnO grown by Metal-Organic Vapor Deposition (MOCVD) and top electrode In2O3 deposited using ionbeam assisted deposition. The top electrode is directly deposited on the guest-host organic material. The design and fabrication considerations for the modulator are also discussed.

Self-assembled electrooptic thin films with remarkably blue-shifted optical absorption based on an X-shaped chromophore.

An "X-shaped" two-dimensional electrooptic (EO) chromophore with extended orthogonal conjugation was designed and synthesized. Self-assembled thin films of this chromophore were fabricated via layer-by-layer chemisorptive siloxane-based self-assembly. The films exhibit a dramatically blue-shifted optical maximum (325 nm) while maintaining a large EO response (chi33(2) approximately 232 pm/V at 1064 nm; r33 approximately 43 pm/V at 1550 nm).

Very large electro-optic responses in H-bonded heteroaromatic films grown by physical vapour deposition.

A crucial goal for modern telecommunications systems is development of very high-speed components for broadband (>100 GHz), all-optical signal/information processing. The core component of such technologies is the electro-optic modulator, which encodes electrical signals onto fibre-optic transmissions. A significant challenge therefore is obtaining materials that have large electro-optic responses and that can be readily fabricated into devices at low cost. We report here on the realization of high-response heteroaromatic organic chromophores that can be straightforwardly self-organized from the vapour phase into intrinsically acentric, high-quality, micrometre-scale films. These pi-conjugated electro-optically active films (with second-order susceptibilities up to approximately 100 pm V(-1)) are thermally stable and conveniently grown by a simple physical vapour deposition process in a few hours. Supramolecular acentricity is achieved without electric field poling, enforced by biomimetic heterocycle-hydroxycarbonyl head-to-tail hydrogen-bonding.

Vapor phase self-assembly of electrooptic thin films via triple hydrogen bonds.

The donor-acceptor pi-electron chromophore 5-{4-[2-(4,6-diamino-[1,3,5]triazin-2-yl)-vinyl]-benzylidene}-pyrimidine-2,4,6-trione (DTPT) was designed and synthesized. Triple H-bonding interactions between neighboring molecules direct self-assembled chromophore alignment in a head-to-tail orientation using a straightforward vapor phase deposition process. Angle-dependent SHG interference patterns and the quadratic dependence of the 532 nm light output intensity on the thickness of the DTPT films for glass substrates coated on both sides demonstrate high, reproducible film quality and uniformity. XRD also demonstrates long-range order in the film and yields a molecular tilt angle in good agreement with polarized SHG data, clearly showing that out-of-plane ordering of chromophore molecules has been achieved.