Nanoscale Charge Accumulation and Its Effect on Carrier Dynamics in Tri-cation Perovskite Structures

Abstract

Nanoscale investigations by scanning probe microscopy have provided major contributions to the rapid development of organic–inorganic halide perovskites (OIHP) as optoelectronic devices. Further improvement of device level properties requires a deeper understanding of the performance-limiting mechanisms such as ion migration, phase segregation, and their effects on charge extraction both at the nano- and macroscale. Here, we have studied the dynamic electrical response of Cs 0.05 (FA 0.83 MA 0.17 ) 0.95 PbI 3– x Br x perovskite structures by employing conventional and microsecond time-resolved open-loop Kelvin probe force microscopy (KPFM). Our results indicate strong negative charge carrier trapping upon illumination and very slow (>1 s) relaxation of charges at the grain boundaries. The fast electronic recombination and transport dynamics on the microsecond scale probed by time-resolved open-loop KPFM show diffusion of charge carriers toward grain boundaries and indicate locally higher recombination rates because of intrinsic compositional heterogeneity. The nanoscale electrostatic effects revealed are summarized in a collective model for mixed-halide CsFAMA. Results on multilayer solar cell structures draw direct relations between nanoscale ionic transport, charge accumulation, recombination properties, and the final device performance. Our findings extend the current understanding of complex charge carrier dynamics in stable multication OIHP structures.

Two birds with one stone: dual grain-boundary and interface passivation enables >22% efficient inverted methylammonium-free perovskite solar cells

“…For the Ref sample, many of the grain boundaries show a ~50-100 mV lower CPD compared to the grains, similarly as previously reported. [152][153][154][155] Such observations have been generally attributed to an enhanced ion and/or defect density, possibly due to a lower energy for defect formation at grain boundary regions. 42,46,154 In contrast, for the GBP sample we observed on average less contrast between grain boundaries and grain interior such that some of them cannot be clearly distinguished in the CPD map and line profiles anymore.…”

Probing Charge Carrier Properties and Ion Migration Dynamics of Indoor Halide Perovskite PV Devices Using Top‐ and Bottom‐Illumination SPM Studies

“…The PV behavior of the PSCs was such that once the light was switched on, the photocurrent sharply increased and remained at a steady‐state, as illustrated in Figure 2l and Figure S4g–I, Supporting Information. This behavior corresponded to the charge‐carrier generation and accumulation processes [ 31 ] over time scales of nanoseconds and seconds, respectively. [ 20,31 ] Upon removing the light, the measured current is negligible, and the relaxation process controls the dynamics of charge carriers and ion migration.…”

“…This behavior corresponded to the charge‐carrier generation and accumulation processes [ 31 ] over time scales of nanoseconds and seconds, respectively. [ 20,31 ] Upon removing the light, the measured current is negligible, and the relaxation process controls the dynamics of charge carriers and ion migration. [ 31 ] Like the charge accumulation process, the relaxation process has been reported to take seconds or even minutes.…”

“…[ 20,31 ] Upon removing the light, the measured current is negligible, and the relaxation process controls the dynamics of charge carriers and ion migration. [ 31 ] Like the charge accumulation process, the relaxation process has been reported to take seconds or even minutes. [ 19 ]…”

Exploring the Capabilities of Scanning Microwave Microscopy to Characterize Semiconducting Polymers

“…It can be used to investigate dielectric [21][22][23] and conductivity [24][25][26] properties. On organic-inorganic trihalides perovskites, Kelvin Force Microscopy (KFM) was also proposed to correlate the material's (photo)conductivity with its structural and morphological properties as they are well known to strongly affect the performances of the corresponding photovoltaic devices [27]. Meanwhile, the ability of dielectric resonators to electrically characterize organic conductors was demonstrated to operate at 9 GHz on a benzothiophene derivative [13].…”