Inter‐Sample and Intra‐Sample Variability in Electronic Properties of Methylammonium Lead Iodide

Abstract

While the challenges associated with the stability of metal halide perovskites are well known and intensely studied, variability in electronic properties represents an equally significant, yet seldom studied, challenge that could potentially slow or inhibit the commercial viability of these systems. In this work, the contactless characterization technique time-resolved microwave conductivity (TRMC) is used to quantify the variability in electronic properties of the prototypical perovskite, methylammonium lead iodide (MAPbI 3 ) both between different samples, and at different locations within the same sample. Using scanning electron microscopy (SEM) and a quasi-automated image-analysis strategy, it is possible to evaluate the metrics of heterogeneity in surface microstructure and correlate them with the electronic properties as obtained by TRMC. Substantial intra-sample and inter-sample variation is observed in the mobility-yield product in samples prepared following differing protocols, and in samples prepared following identical protocols.

Establishing Self‐Dopant Design Principles from Structure–Function Relationships in Self‐n‐Doped Perylene Diimide Organic Semiconductors

“…It should be noted that unlike electrical measurements, where charges must travel ≈µm to be extracted and hence detectable, TRMC is a local probe, so the relationship between mobility and morphology can be distinct. [ 65 ] More importantly, these results provide direct evidence that changes in carrier mobility in self‐n‐doped PDIs are relatively unsubstantial and cannot account for the large increases in electrical conductivity typically observed in these materials following annealing. This result also provides indirect evidence that doping primarily generates free carriers, though future work in this area could establish the branching ratio between bound states and free carriers.…”

Role of A‐Site Composition in Charge Transport in Lead Iodide Perovskites

“…[32] It is important to reiterate that the data presented in Figure 3 is the mean of three identically processed samples for every condition and that TRMC measures electronic properties over a macroscopic area (defined by laser spot size). We know that microstructure [29,35] and phase [44] have a significant impact on charge transport in this class of materials, so we would expect differences in parameters depending on processing, but we interpret the presented values as the representative average for each composition.…”

“…We have shown that, for our processing and measurement protocols at least, surface morphology is not strongly correlated with . [ 29 ] Another possibility is that the average structure of the perovskite is modified, and the electronic structure also changes. A simple way to quantify the structure of perovskites is using the Goldschmidt tolerance factor, [ 60 ] defined by Equation ().…”

“…Reproducibility is another issue that not only inhibits commercialization of perovskites, [ 27 ] but also makes it challenging to make consistent and reproducible statements on perovskite properties. [ 28,29 ] In this study we prepared three samples for each composition and draw conclusions based on averages of the figure of merit, rather than individual samples.…”

“…Reproducibility is another issue that not only inhibits commercialization of perovskites, [27] but also makes it challenging to make consistent and reproducible statements on perovskite properties. [28,29] In this study we prepared three samples for each composition and draw conclusions based on averages of the figure of merit, rather than individual samples. The mobility of charge carriers in solar cells is a critical factor in performance, as faster moving charges are more likely to be extracted before recombining than slower charges.…”