Evidence of Tailoring the Interfacial Chemical Composition in Normal Structure Hybrid Organohalide Perovskites by a Self-Assembled Monolayer

Abstract

Current-voltage hysteresis is a major issue for normal architecture organo-halide perovskite solar cells. In this manuscript we reveal a several-angstrom thick methylammonium iodide-rich interface between the perovskite and the metal oxide. Surface functionalization via self-assembled monolayers allowed us to control the composition of the interface monolayer from Pb poor to Pb rich, which, in parallel, suppresses hysteresis in perovskite solar cells. The bulk of the perovskite films is not affected by the interface engineering and remains highly crystalline in the surface-normal direction over the whole film thickness. The subnanometer structural modifications of the buried interface were revealed by X-ray reflectivity, which is most sensitive to monitor changes in the mass density of only several-angstrom thin interfacial layers as a function of substrate functionalization. From Kelvin probe force microscopy study on a solar cell cross section, we further demonstrate local variations of the potential on different electron-transporting layers within a solar cell. On the basis of these findings, we present a unifying model explaining hysteresis in perovskite solar cells, giving an insight into one crucial aspect of hysteresis for the first time and paving way for new strategies in the field of perovskite-based opto-electronic devices.

Imaging Metal Halide Perovskites Material and Properties at the Nanoscale

“…[62] The extent of J-V hysteresis can be controlled by engineering a PbI 2 -rich interfacial region that serves to balance the electric field generated by the mobile ions accumulated nearby. [63] The results outlined in this section highlight the ability of AFM functional imaging to identify the impact of fabrication optimization.…”

How the formation of interfacial charge causes hysteresis in perovskite solar cells

“…Rather, the charge is stabilized directly at the perovskite/SnO 2 interface, e.g. by the molecular interface structure 38 or chemical reactions. 10,13 The absence of negative space charges in the perovskite layer suggests that the dynamics of the mobile ions are much faster than we could resolve in our measurements and thus play no role for the observed decay dynamics.…”

A Short Review on Interface Engineering of Perovskite Solar Cells: A Self‐Assembled Monolayer and Its Roles

“…Also, their functional groups interact with perovskite materials and affect crystal formation . Lastly, SAMs could tailor the interfacial composition between a metal oxide and perovskite layer, facilitating charge extraction and improving device performance . SAMs make an interfacial layer change from Pb‐rich to Pb‐poor composition, facilitating charge extraction and improving device performance.…”