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Artigo em Inglês | MEDLINE | ID: mdl-32394700


Quasi-two-dimensional (Q-2D) perovskites featured with multiple dimensional quantum wells (QWs) have been the main candidates for optoelectronic applications. However, the excessive low-dimensional perovskite is unfavorable to the device efficiency due to the phonon-exciton interaction and the inclusion of insulating large organic cation. Herein, the low-dimensional QWs formation is suppressed by removing the organic cation 1-naphthylmethylamine iodide (NMAI) through the ultra-high vacuum (UHV) annealing. The perovskite light-emitting diodes (PLEDs) devices based on films annealed with optimized UHV conditions show higher external quantum efficiency of 13.0% and wall-plug efficiency of 11.1% compared to otherwise identical devices with films annealed in a glovebox.

Artigo em Inglês | MEDLINE | ID: mdl-32412132


Environmentally friendly halide double perovskites with improved stability are regarded as a promising alternative to lead halide perovskites. The benchmark double perovskite, Cs2AgBiBr6, shows attractive optical and electronic features, making it promising for high-efficiency optoelectronic devices. However, the large bandgap limits its further applications, especially for photovoltaics. Herein, we develop a novel crystal-engineering strategy to significantly decrease the bandgap by ~0.26 eV, reaching the smallest reported bandgap of 1.72 eV for Cs2AgBiBr6 at ambient conditions. The bandgap narrowing is confirmed by both absorption and photoluminescence measurements. Our first-principles calculations indicate that enhanced Ag-Bi disorder has a large impact on the band structure and decreases the bandgap, providing a possible explanation of the observed bandgap narrowing effect. This work provides new insights for achieving lead-free double perovskites with suitable bandgaps for optoelectronic applications.

Adv Mater ; 30(22): e1707143, 2018 May.
Artigo em Inglês | MEDLINE | ID: mdl-29682798


Effective passivation and stabilization of both the inside and interface of a perovskite layer are crucial for perovskite solar cells (PSCs), in terms of efficiency, reproducibility, and stability. Here, the first formamidinium lead iodide (δ-FAPbI3 ) polymorph passivated and stabilized MAPbI3 PSCs are reported. This novel MAPbI3 /δ-FAPbI3 structure is realized via treating a mixed organic cation MA x FA1-x PbI3 perovskite film with methylamine (MA) gas. In addition to the morphology healing, MA gas can also induce the formation of δ-FAPbI3 phase within the perovskite film. The in situ formed 1D δ-FAPbI3 polymorph behaves like an organic scaffold that can passivate the trap state, tunnel contact, and restrict organic-cation diffusion. As a result, the device efficiency is easily boosted to 21%. Furthermore, the stability of the MAPbI3 /δ-FAPbI3 film is also obviously improved. This δ-FAPbI3 phase passivation strategy opens up a new direction of perovskite structure modification for further improving stability without sacrificing efficiency.

ACS Appl Mater Interfaces ; 8(45): 31413-31418, 2016 Nov 16.
Artigo em Inglês | MEDLINE | ID: mdl-27797470


Recently, perovskite solar cells with high photovoltaic performance based on methylammonium lead halide have attracted great interest due to the superior physical properties of the perovskite optical absorption layer. Here, we investigate the interface carrier transport properties of CH3NH3PbI3 film by applying the reported treatment with methylamine gas, to reveal the possible mechanism of high performance perovskite-sensitized solar cell results. It is found that the crystal structure and surface morphology are effectively improved by the room-temperature repair of methylamine atmosphere. The preferred 110 orientation results in a slightly larger band gap, which may contribute to the better energy level matching and carrier transport. Further investigations on relaxation time and electron mobility confirm the significantly enhanced carrier diffusion length, revealing the important role of optimized crystallization on charge transport properties, which may be helpful to seek high-powered perovskite solar cells by optimizing the perovskite synthetic process.

Angew Chem Int Ed Engl ; 55(47): 14723-14727, 2016 11 14.
Artigo em Inglês | MEDLINE | ID: mdl-27766739


Methylamine-induced thin-film transformation at room-temperature is discovered, where a porous, rough, polycrystalline NH4 PbI3 non-perovskite thin film converts stepwise into a dense, ultrasmooth, textured CH3 NH3 PbI3 perovskite thin film. Owing to the beneficial phase/structural development of the thin film, its photovoltaic properties undergo dramatic enhancement during this NH4 PbI3 -to-CH3 NH3 PbI3 transformation process. The chemical origins of this transformation are studied at various length scales.

Chem Commun (Camb) ; 52(19): 3828-31, 2016 Mar 07.
Artigo em Inglês | MEDLINE | ID: mdl-26867948


High-quality formamidinium lead iodide (FAPbI3) perovskite thin films are fabricated via organic cation exchange. With ammonia lead iodide (NH4PbI3) as the starting material, the NH4(+) in NH4PbI3 could be gradually substituted by FA(+) in formamidine acetate (FA-Ac) and simultaneously transformed to the pure phase α-FAPbI3 at elevated temperature.