Lead-Free Cesium Titanium Bromide Double Perovskite Nanocrystals

Abstract

Double perovskites are a promising family of lead-free materials that not only replace lead but also enable new optoelectronic applications beyond photovoltaics. Recently, a titanium (Ti)-based vacancy-ordered double perovskite, Cs2TiBr6, has been reported as an example of truly sustainable and earth-abundant perovskite with controversial results in terms of photoluminescence and environmental stability. Our work looks at this material from a new perspective, i.e., at the nanoscale. We demonstrate the first colloidal synthesis of Cs2TiX6 nanocrystals (X = Br, Cl) and observe tunable morphology and size of the nanocrystals according to the set reaction temperature. The Cs2TiBr6 nanocrystals synthesized at 185 °C show a bandgap of 1.9 eV and are relatively stable up to 8 weeks in suspensions. However, they do not display notable photoluminescence. The centrosymmetric crystal structure of Cs2TiBr6 suggests that this material could enable third-harmonic generation (THG) responses. Indeed, we provide a clear evidence of THG signals detected by the THG microscopy technique. As only a few THG-active halide perovskite materials are known to date and they are all lead-based, our findings promote future research on Cs2TiBr6 as well as on other lead-free double perovskites, with stronger focus on currently unexplored nonlinear optical applications.

Titanium‐Based Vacancy‐Ordered Double Halide Family in Perovskite Solar Cells

“…[ 42 ] The impact of synthesis parameters such as reaction temperature and capping ligands on the structural stability and morphology of Cs 2 TiBr 6 nanocrystal was explained comprehensively by Grandhi and his co‐workers. [ 43 ] Tuning the hot‐injection temperature is key in controlling the morphology and size of the final nanocrystal end product. Varied injection temperatures ranging between 90 and 245 °C were investigated.…”

Optimization of Hole and Electron Transport Layer for Highly Efficient Lead-Free Cs2TiBr6-Based Perovskite Solar Cell

“…The direct-energy-bandgap perovskite compound Cs 2 TiBr 6 is a promising material that has very good optical, electrical, and photovoltaic properties and may replace methylammonium lead halide perovskite for next-generation photovoltaic applications [9][10][11]. On the other hand, robust titanium (Ti) makes Cs 2 TiBr 6 a tolerable and stable perovskite Photonics 2022, 9, 23 2 of 15 semiconductor [12]. In this regard, the pioneering work was carried out by Chen and co-authors, and they investigated the photovoltaic response of the Cs 2 TiBr 6 -based solar cell, where TiO 2 /C 60 was used as an electron transport layer and P 3 HT was used as a hole transport layer for PCEs up to 3.12% [9].…”

Investigating the theoretical performance ofCs2TiBr6‐based perovskite solar cell with La‐dopedBaSnO3andCuSbS2as the charge transport layers

“…5 Ti-based A 2 +1 Ti +4 X 6 À1 double perovskites are leadfree and nontoxic materials that not only can substitute the lead in perovskite but also possess novel optoelectronic applications besides solar cells. 6 According to the density functional theory (DFT) calculations, these HPs have advantageous electronic and optical properties, such as appropriate bandgaps and tuneable defect properties.…”

“…It exhibits prolonged carrier-diffusion lengths, efficient photoluminescence, as well as energy levels appropriate for the usage in tandem solar cells. 6 Besides, it demonstrates superior thermal, moisture, and light effects stability than the methylammonium lead iodide (MAPbI 3 ) thin films, ensuring the higher intrinsic or environmental durability of the Cs 2 TiBr 6 thin films. 7 Moreover, Cs 2 TiBr 6 -based PSC has attained 3.3% efficiency experimentally that is greater than most other double PSCs.…”