Synthesis, Characterization, and Morphological Control of Cs₂CuCl₄ Nanocrystals

Abstract

Recently, there has been an increase in research relating to the search for new optoelectronic materials for photovoltaic devices and light-emitting diodes. This research focuses on developing materials that not only possess the required optoelectronic properties (high absorption, efficient photon emission, and high charge-carrier mobilities) but are also solution-processable, which can reduce fabrication costs. Ternary ionic crystal structures, such as lead-halide perovskites, have emerged as a class of such suitable materials. However, the most promising structures, which exhibit the highest device efficiencies, rely on toxic lead as a cationic species, thereby hindering commercial application. Here, we synthesize and characterize CsCuCl3 and Cs2CuCl4 nanocrystals. These nanocrystals exhibit bright broad band green emission from copper defects when excited below 300 nm. We show that by employing a variety of ratios of coordinating solvents during synthesis, we can tailor the morphology of the nanoparticles produced, allowing us to produce structures such as dots, platelets, and rods. These materials represent a new class of nontoxic, solution-processable ternary semiconductors for optoelectronic applications.

A Lead‐Free All‐Inorganic Metal Halide with Near‐Unity Green Luminescence

“…reported a green‐light emitter Cs 2 CuCl 4 which can also be synthesized via a modified hot injection method. [ 27 ] For β‐Cs 3 Cu 2 Cl 5 , the Cs‐oleate precursor was prepared by treating CuCl with oleylamine and the reaction was conducted at N 2 atmosphere. Hence, the possibility of forming Cu(II) compounds is small.…”

“…In addition, compared to β‐Cs 3 Cu 2 Cl 5 , Cs 2 CuCl 4 shows different optical properties with blueshifted excitation peak of 285 nm and redshifted emission peak of 525 nm. [ 27 ] However, the photoluminescence excitation (PLE) spectra of β‐Cs 3 Cu 2 Cl 5 with different emission wavelengths show the same peak (Figure 2f), suggesting the emissive species come from identical excited‐states, further ruling out the possibility of having Cs 2 CuCl 4 emitter impurities. Consequently, the near‐unity green luminescence only originates from β‐Cs 3 Cu 2 Cl 5 .…”

“…[ 19,22–26 ] However, to our knowledge, for another one of the three primary colors of light, the PLQY of the reported lead‐free green‐light emitting metal halides, especially all‐inorganic semiconductors, is far behind the performance of lead halide perovskites. [ 12,27 ]…”

Recent Advances and Opportunities of Lead-Free Perovskite Nanocrystal for Optoelectronic Application

“…In addition to the LARP technique, the high-temperature HI method was also proposed by Booker et al to prepare the Cu-based halide NCs [231]. By changing the ratio of OA and OAm, a series of Cs 2 CuCl 4 NCs with different morphologies (QDs, NPLs, NRs, and NWs) and sizes (6-300 nm) were obtained (Figures 9(f)-9(k)).…”

“…Detailedly, the nanomaterials are QDs with a variety of particle sizes (2 : 1, 4 : 1, and 1 : 4), NRs with an average length of 1.2 μm (1 : 2), NPLs with a 200 nm radius (2 : 2), and NWs with a length over 2 μm but only 50 nm wide (4 : 4). This is because different coordination solvents can significantly affect the NC morphology via either orientated attachment or inhibition or promotion of different growth facets [231]. All these nanomaterials exhibited quite broad emission spectra with an emission peak at 525 nm, possibly because of the copper defects inside the NCs.…”