Spatially inhomogeneous photoluminescence-voltage hysteresis in planar heterojunction perovskite-based solar cells

Abstract

Spatially resolved photoluminescence (PL) of methylammonium lead iodide (MAPbI3) films in planar heterojunction solar cells is probed by time-resolved confocal microscopy to study the interface effect on PL intensity-voltage (PL-V) hysteresis. Negligible PL-V hysteresis is observed at the interfacial area, while significant hysteresis is observed in the bulk film. PL lifetime imaging of the perovskite device reveals inhomogeneous charge extraction due to variation of the interfacial contact quality. Poor interfacial contact leads to more severe PL-V hysteresis in the bulk perovskite film. The PL-V characteristics also suggest that voltage-driven ion migration may lead to redistribution of charge traps, and consequently affect the nonradiative charge recombination and the PL intensity in MAPbI3 films.

Morphology and Photoluminescence of CH3NH3PbI3 Deposits on Nonplanar, Strongly Curved Substrates

“…For example, such branched structures can be seen in Figure S9 for MAPbI 3 deposits on cylinder-shaped quartz rods having diameters of 400 and 700 μm. In fact, the star-like structures present on cylindrical substrates with larger diameters are similar to these reported by Nie et al for hot-casting of thins films of MAPbI 3 on flat substrates or by Xu et al for MAPbI 3 thin films deposited onto a flat glass substrate (indium tin oxide) covered with a compact layer of TiO 2 . Moreover, the optical microscopy image in Figure S4(a) also shows the presence of branched and interconnected ribbons of MAPbI 3 deposited onto a flat glass surface, while employing the one-step solution coating and analogous annealing conditions as used for coating the cylindrical substrates.…”

“…As suggested by Xu et al, the space in between the branched and interconnected micrometersized ribbons is also partially filled with smaller, more disordered "spherulitic" crystalline structures of MAPbI3. 28 Overall, the SEM images presented in Figure 2 revealed a strong relationship between the morphology of MAPbI3 deposits and the substrate curvature. In particular, for the cylinder-shaped quartz substrates with diameters within the range from 80 to 1800 μm, the average sizes of polycrystalline microwires evolved from 100 nm to 8 μm (width) and 5 μm to 150 μm (length).…”

“…It has to be stressed that the “voids”, which occur for practically all the deposits presented in Figure , are not really free of MAPbI 3 . As suggested by Xu et al, the space in between the branched and interconnected micrometer-sized ribbons is also partially filled with smaller, more disordered “spherulitic” crystalline structures of MAPbI 3 …”

Self-Powered Perovskite/CdS Heterostructure Photodetectors

“…In an effort to better understand the charge separation process at the MAPbI 3 /CdS heterointerface, time-resolved PL measurements were carried out (Figure ). The time-resolved traces reflect the transient evolution of the electron–hole population after excited by the impulsive laser, and the measured transient decay process of the excited state can be fitted by using where I 0 is the initial intensity, w i is i th amplitude, τ i is the lifetime . As shown in Figure a, i = 1 was utilized for the pristine MAPbI 3 because of its single exponential decay.…”

“…where I 0 is the initial intensity, w i is ith amplitude, τ i is the lifetime. 46 As shown in Figure 2a, i = 1 was utilized for the pristine MAPbI 3 because of its single exponential decay. The fitting yields a lifetime of 43.5 ns, which is close to previously reported values.…”