Guanidinium substitution-dependent phase transitions, ionic conductivity, and dielectric properties of MAPbI₃

Abstract

Over the past few years of boosting studies in halide perovskites, the formulation of guanidinium (GA+)-containing compounds has been proven to be an excellent strategy. A system in particular, namely...

Improvement in the Performance of Inverted 3D/2D Perovskite Solar Cells by Ambient Exposure

“…Perovskite solar cells (PSCs) have attracted increased attention in recent years due to their high efficiency. [ 1–50 ] However, various instabilities under normal operating conditions (exposure to ambient air/moisture, illumination, elevated temperature, etc.) have been hindering the efforts in PSC commercialization.…”

Intrinsic aging in mixed-cation lead halide perovskites

“…In the GA x MA 1− x PbI 3 system, the ionic conductivity was shown to be inversely proportional to the guanidinium content. 59 Having that in mind, we can rationalize our results by the following. In MAPbI 3 , the grain growth driving force is mainly due to GB area reduction and internal stress relief.…”

“…1(a), the important regions to identify the crystal structures of each composition and other phases eventually present are shown. As discussed recently, 59 the x = 0.0 and x = 0.1 compositions are tetragonal at room temperature, whereas the composition x = 0.2 was taken as a cubic perovskite. From the phase composition perspective, the first interesting feature observed in the XRD results is the absence of PbI 2 formation in all compositions regardless of the aging time, except for x = 0.2 where a small PbI 2 peak was already present in the pristine sample.…”

“…As a result, neither driving force nor kinetic conditions greatly favor the grain growth, making x = 0.1 the most stable against grain growth at RT among the studied compositions. It is also necessary to consider that the activation energy for ion transport in these compositions has the same tendency, that is, MAPbI 3 < GA 0.2 MA 0.8 PbI 3 < GA 0.1 MA 0.9 PbI 3 , 59 which certainly has its role in the observed stability against grain growth. In all compositions, the grain size distributions broaden with aging time, which is a signature of larger grains growing at the expense of the smaller grains, as expected in sintering processes.…”

“…To synthesize the GA x MA 1− x PbI 3 polycrystalline samples, we used the procedure described in ref. 59. Amounts of PbI 2 (Sigma-Aldrich, 211168, 99%), MAI (Sigma-Aldrich, 98%), and GAI (Sigma-Aldrich, 99%) were weighted in desired proportions and dissolved to 0.75 mol l −1 solutions in a mixture consisting in 70 v% of DMF (Sigma Aldrich, 99.8%) and 30 v% of DMSO (Sigma Aldrich, 99.9%).…”