Optimizing the quasi-equilibrium state of hot carriers in all-inorganic lead halide perovskite nanocrystals through Mn doping: fundamental dynamics and device perspectives

Abstract

Hot carrier (HC) cooling accounts for the significant energy loss in lead halide perovskites (LHPs) solar cells. Here, we study HC relaxation dynamics in Mn-doped LHP CsPbI3 nanocrystals (NCs), combining...

Modulating the Carrier Relaxation Dynamics in Heterovalently (Bi3+) Doped CsPbBr3 Nanocrystals

“…21 the enhanced carrier−phonon coupling and a decreased HC cooling rate at band-edge excitation due to the enhanced LO acoustic phonon bandgap in Mn 2+ -doped CsPbBI 3 NCs. 29 The limitation of the isovalent atom doping is that there is no change in the concentration of the charge carrier after doping, which is a primary requirement to improve the carrier transport property of NCs. 19,30 Thus, the doping of a heterovalent atom (i.e., Au 3+ , Bi 3+ , Sb 3+ , or Nd 3+ ) is beneficial for the enhanced charge carrier concentration, structural stability, and partial reduction of the toxicity of lead in LHPs.…”

“…Primarily, isovalent atom doping (such as Mn 2+ , Sn 2+ , Cu 2+ , Cd 2+ , or Ca 2+ ) for the lead ion (Pb 2+ ) has been established to improve the optical, electrical, and magnetic properties in LHP NCs. − Recently, there has been a great effort to slow the HC cooling by Zn 2+ doping in CsPbI 2 Br NCs at a low carrier density . Zheng et al have demonstrated recently the increase in the HC cooling rate with a higher excitation energy due to the enhanced carrier–phonon coupling and a decreased HC cooling rate at band-edge excitation due to the enhanced LO acoustic phonon bandgap in Mn 2+ -doped CsPbBI 3 NCs . The limitation of the isovalent atom doping is that there is no change in the concentration of the charge carrier after doping, which is a primary requirement to improve the carrier transport property of NCs. , Thus, the doping of a heterovalent atom (i.e., Au 3+ , Bi 3+ , Sb 3+ , or Nd 3+ ) is beneficial for the enhanced charge carrier concentration, structural stability, and partial reduction of the toxicity of lead in LHPs. ,− Among the different choices of heterovalent atoms, less toxic bismuth (Bi 3+ ) is frequently used as a dopant in LHPs because its ionic radius and electronic structure are similar to those of Pb 2+ .…”

“…We have observed the temperature of the electronic pool, which is coupled to the pool of LO phonons through dominant Fröhlich interactions. The LO phonon pool then efficiently transfers energy to the longitudinal acoustic (LA) phonon pool due to the anharmonicity of the vibrations and finally releases their heat energy to the surrounding environment. ,, To gain further insight into the different stages of HC relaxation pathways of CsPbBr 3 NCs due to heterovalent Bi doping, we have calculated the energy loss rate per carrier ( J r ) from the extracted T C by the following equation: , Figure d shows the comparison of J r (solid spheres) versus the carrier temperature between undoped and 5% Bi-doped CsPbBr 3 at 400 nm excitation with an n 0 of 1.19 × 10 17 cm –3 . It is clear that 5% Bi-doped CsPbBr 3 NCs exhibit a J r (from 0.21 to 0.009 eV/ps) that is much higher than that of undoped CsPbBr 3 NCs (from 0.11 to 0.002 eV/ps) until T C reaches 300 K, indicating faster HC cooling for doped samples.…”

“…Notably, the decrease in J r is much slower as T C approaches the lattice temperature ( T L ). Moreover, the J r of HCs is primarily influenced by the emission and decay of LO phonons. , The initial high energy loss rate (i.e., the rapid HC cooling) with a larger T C can be ascribed to the efficient LO phonon emission through the dominant Fr̈ohlich interaction that dissipates the excess energy of the HC. , This LO phonon decays into counterpropagating LA phonons by dominating the symmetric Klemens channel and antisymmetric Ridley channel until the T C decreases to the lattice temperature . Hence, slower HC cooling as T C approaches T L signifies the thermal equilibration between LO phonons and acoustic phonons.…”

Combining two-photon photoemission and transient absorption spectroscopy to resolve hot carrier cooling in 2D perovskite single crystals: the effect of surface layer

“…Recently the potential of three-dimensional (3D) hybrid perovskites in the application of HCSC has attracted increasing attention. [13][14][15][16] Firstly, the small effective mass of the charge carriers leads to slower HC relaxation by diminishing the possible intraband Auger-type energy transfer that promotes energy losses. 17,18 Secondly, the large phonon bandgap between longitudinal optical (LO) and longitudinal acoustic (LA) phonon branches of 4 halide perovskite suppresses the pathways in the phonon decay, thereby enhancing the hot phonon bottleneck effect.…”