ABSTRACT
Photoinduced phase separation in mixed halide perovskites emerges from their electro-mechanical properties and high ionic conductivities, resulting in photoinduced I--rich charge carrier traps that diminish photovoltaic performance. Whether photoinduced phase separation stems from the polycrystalline microstructure or is an intrinsic material property has been an open question. We investigate the nanoscale photoinduced behavior of single-crystal mixed Br-/I- methylammonium (MA+) lead halide perovskite (MAPb(Br xI1- x)3) nanoplates, eliminating effects from extended structural defects. Even in these nanoplates, we find that phase separation occurs, resulting in I--rich clusters that are nucleated stochastically and stabilized by polarons. Upon lowering the electron-phonon coupling strength by partially exchanging MA+ for Cs+, a phase-separated steady state is not reached, nevertheless transient I- clustering still occurs. Our results, supported by multiscale modeling, demonstrate that photoinduced phase separation is an intrinsic property of mixed halide perovskites, the extent and dynamics of which depends on the electron-phonon coupling strength.
ABSTRACT
Controlling the flow of thermal energy is crucial to numerous applications ranging from microelectronic devices to energy storage and energy conversion devices. Here, we report ultralow lattice thermal conductivities of solution-synthesized, single-crystalline all-inorganic halide perovskite nanowires composed of CsPbI3 (0.45 ± 0.05 W·m-1·K-1), CsPbBr3 (0.42 ± 0.04 W·m-1·K-1), and CsSnI3 (0.38 ± 0.04 W·m-1·K-1). We attribute this ultralow thermal conductivity to the cluster rattling mechanism, wherein strong optical-acoustic phonon scatterings are driven by a mixture of 0D/1D/2D collective motions. Remarkably, CsSnI3 possesses a rare combination of ultralow thermal conductivity, high electrical conductivity (282 S·cm-1), and high hole mobility (394 cm2·V-1·s-1). The unique thermal transport properties in all-inorganic halide perovskites hold promise for diverse applications such as phononic and thermoelectric devices. Furthermore, the insights obtained from this work suggest an opportunity to discover low thermal conductivity materials among unexplored inorganic crystals beyond caged and layered structures.
ABSTRACT
The nanowire and nanorod morphology offers great advantages for application in a range of optoelectronic devices, but these high-quality nanorod arrays are typically based on high temperature growth techniques. Here, we demonstrate the successful room temperature growth of a hybrid perovskite (CH3NH3PbBr3) nanorod array, and we also introduce a new low temperature anion exchange technique to convert the CH3NH3PbBr3 nanorod array into a CH3NH3PbI3 nanorod array while preserving morphology. We demonstrate the application of both these hybrid perovskite nanorod arrays for LEDs. This work highlights the potential utility of postsynthetic interconversion of hybrid perovskites for nanostructured optoelectronic devices such as LEDs, which enables new strategies for the application of hybrid perovskites.
