Photoinduced Anion Exchange in Cesium Lead Halide Perovskite Nanocrystals

Abstract

Cesium lead halide (CsPbX) perovskite nanocrystals (NCs) possess the unique capability of post-synthesis anion exchange providing facile tunability of the optical properties, which is usually achieved by mixing NCs with reactive anion precursors. In this work, we show that the controllable anion exchange can be achieved in a dihalomethane solution of CsPbX NC in the absence of any spontaneously reacting anion source using photoexcitation of CsPbX NCs as the triggering mechanism for the halide ion exchange. The reaction begins with the photoinduced electron transfer from CsPbX NCs to dihalomethane solvent molecules producing halide ions via reductive dissociation, which is followed by anion exchange. The reaction proceeds only in the presence of excitation light and the rate and extent of reaction can be controlled by varying the light intensity. Furthermore, the asymptotic extent of reaction under continuous excitation can be controlled by varying the wavelength of light that self-limits the reaction when light becomes off-resonance with the absorption of NCs. The light-controlled anion exchange demonstrated here can be utilized to pattern the post-synthesis chemical transformation of CsPbX NCs, not readily achievable using typical methods of anion exchange.

Photoelectrochemically Active and Environmentally Stable CsPbBr3/TiO2 Core/Shell Nanocrystals

“…The conduction band and valence band edge of the CsPbBr 3 NCs is ≈−1.0 and ≈1.5 V versus the normal hydrogen electrode (NHE), respectively. [24] While the conduction band and valence band edge of TiO 2 (anatase) were determined to be ≈−0.5 and ≈2.7 V versus NHE, respectively. [25] Therefore, a type II band alignment with an offset of conduction band (≈−0.5 V) and valence band (≈1.2 V) could form in the CsPbBr 3 /TiO 2 heterostructure.…”

Halide Perovskite Nanocrystals for Next‐Generation Optoelectronics

“…In addition, the large difference in ionic radii between Cl − and I − anions explains why the direct exchange between Cl − and I − anions involves a structural stress on the perovskite lattice, which results in serious degradation of the nanocrystals. Other studies on the halide anion exchange have also been reported, such as halide exchange in solid phase, in the forms of nanorod arrays, nanowires, or nanocubes, photoinduced anion exchange, and gaseous hydrogen halides as the halide precursors …”

Unveiling the Photo‐ and Thermal‐Stability of Cesium Lead Halide Perovskite Nanocrystals

“…CsPbX 3 nanocrystals have been incorporated into solar cells achieving a record 13.4 % power conversion efficiency (PCE). [15] Other syntheses have expanded this general idea by generating multiple nanocrystal morphologies through ligand mediation [21][22] and reaction tuning, [23] by using different surface ligands for improved quantum yields, [24][25] by increasing surface passivation/repair via salt solutions, [26][27][28][29] as well as by generating other cation/anion compositions through doping [17,[30][31][32][33][34][35] or post-synthetic ion exchange. [12,[19][20] Most reported syntheses of CsPbX 3 follow the work of Protesescu et al who demonstrated a simple, solution-based synthesis for nanocrystals with high luminescence.…”

“…[12,[19][20] Most reported syntheses of CsPbX 3 follow the work of Protesescu et al who demonstrated a simple, solution-based synthesis for nanocrystals with high luminescence. [15] Other syntheses have expanded this general idea by generating multiple nanocrystal morphologies through ligand mediation [21][22] and reaction tuning, [23] by using different surface ligands for improved quantum yields, [24][25] by increasing surface passivation/repair via salt solutions, [26][27][28][29] as well as by generating other cation/anion compositions through doping [17,[30][31][32][33][34][35] or post-synthetic ion exchange. [19,22,[36][37][38][39] In addition, triple-cation (Cs,formamidinium,methylammonium)PbX 3 materials have been developed with the goal of increasing stability while maintaining bright luminescence.…”