Composition and Dimensionality Engineering of Perovskite Materials for Photovoltaic Applications

Abstract

In recent years, metal halide perovskites have attracted research interest due to their remarkable optoelectronic properties, including strong optical absorption and long carrier diffusion lengths, combined with low-cost fabrication. As soft ionic solids, metal halide perovskites exhibit versality in chemical composition and structural dimensionality: this enables tunable bandgaps and luminescence. In this thesis, I focus on engineering the composition and dimensionality of metal halide perovskites with the goal of advancing photovoltaic applications.

I begin by developing and investigating a cation-engineering strategy that enables wide-bandgap perovskites to show high defect-tolerance. Cation-engineering increases the device performance of wide-bandgap perovskite solar cells to exceed 20% PCE. I attribute the excellent performance to the reorientation of MA dipoles, which heals deep-level defects.

Next, I study carrier diffusion in mixed-cation perovskites. MA-based perovskite thin films exhibit a high carrier diffusivity of 0.047 cm²s^-1, whereas CsFA films show an order of magnitude lower carrier diffusivity. Experimental characterization suggests that the graded composition of CsFA films curtails electron diffusion. The incorporation of MA leads to a uniform composition of CsMAFA films, giving rise to a diffusivity of 0.034 cm²s^-1.

I then explore dimensionality engineering in narrow-bandgap perovskites. I develop a processing approach that enables the passivation of 3D perovskite surfaces using ultra-thin 2D perovskite passivants. The 2D layer retards the oxidation of 3D perovskites while maintaining their charge-transport properties. This enables a certified PCE of 18.95% and a 200-hour operating stability for narrow-bandgap perovskite solar cells.

Lastly, I study perovskite nanoplatelet (PNPL) synthesis and phase-control, as well as energy transfer within mixed-phase PNPLs. I find that tuning the phase-distribution of PNPLs engineers their photoluminescence quantum yield and Stokes shift, allowing the corresponding perovskite luminescent solar concentrators to exhibit low optical loss.

This work showcases the crucial role of composition and dimensionality in extending the applicability of perovskites to tandem and building-integrated photovoltaics. It concludes with a discussion of paths towards the eventual commercialization of these PV technologies, in light of the need to improve their efficiency and stability, to achieve up-scaling, and to address concerns regarding material toxicity.