Illumination‐Induced Halide Segregation in Gradient Bandgap Mixed‐Halide Perovskite Nanoplatelets

Abstract

Efficient energy funneling has exhibited great contribution to the high performance of perovskite‐based optoelectronic devices. Here, formamidinium (FA+, HC(NH2)2+) lead mixed‐halide nanoplatelets (FAPb(BrxI1−x)3) with gradient bandgap are fabricated using chemical vapor deposition followed with bromide–iodide substitution by exposure to FABr vapor. The as‐fabricated perovskite nanoplatelets exhibit pure bromide phase in the thin nanoplatelet (tens of nanometers) and a gradual bromide–iodide composite, thus with gradient bandgap (2.29–1.56 eV), in the thick nanoplatelet (more than hundreds of nanometers). Accordingly, photoluminescence (PL) spectra are observed at 540, 560/610, and 735/790 nm, respectively. In such gradient bandgap structures, photogenerated carriers can effectively transfer and emit in the low‐bandgap region by energy funneling. With illumination, the PL spectrum of Br‐rich phase exhibits blueshift and therefore 610 nm band disappears. In contrast, redshift is observed in I‐rich phase due to the decrease of 735 nm band while an increase of 790 nm band. It is demonstrated that irreversible and stable phases are formed with illumination in both Br‐rich and I‐rich nanoplatelets. This investigation develops a method to fabricate gradient bandgap perovskites with designed energy funneling, and also provides significant insight into the halide segregation in such special perovskites, which greatly benefits their future optoelectronic applications.

Highly Efficient Charge Transfer between Perovskite Nanocrystals and g‐C3N4 Nanosheets

“…[38][39][40] Moreover, the CsPb(Br x I 1Àx ) 3 nanocrystal is a kind of mixed-halide perovskite; the Br phase and I phase separate during the illumination due to ion migration, which induces the formation of an I-rich phase, thus causing the PL position redshift. [41] Photodegradation effects similar to the results shown in Figure 4a are also observed for PNCs and PNC/CN. However, as shown in Figure 4b, the degradation rates are strikingly different.…”

Flexible, Printable Soft‐X‐Ray Detectors Based on All‐Inorganic Perovskite Quantum Dots

“…To enhance the crystal sensitivity, we effectively reduced the surface defects and controllably tuned the crystallinity via chemistry engineering. These monocrystalline QDs are phase stable at room temperature and under illumination in comparison with other organic–inorganic perovskites . Therefore, they can sustain high performance in terms of optoelectronic functionalities under various stress conditions.…”

A Review of Perovskite Photovoltaic Materials’ Synthesis and Applications via Chemical Vapor Deposition Method

“…These results suggest that 2D materials such as MoS 2 and WS 2 can be promising candidates for the formation of hole extraction layers in the PSCs. FAPb(Br x I 1−x ) 3 nanoplatelets with gradient bandgap are fabricated using CVD method [100]. During the whole vapor conversion process, CVD furnace temperature was 140 °C, and pressure was about 500 mTorr with a controlled Ar gas flow rate of 35 sccm (standard cubic centimeters per minute) and reaction time 2 h.…”