Halide perovskite-based photovoltaics – from materials to devices

Abstract

Oxide perovskite materials have occupied a very important position in functional materials such as ferroelectric, piezoelectric, thermoelectric, and even superconducting. They are represented by the general formula ABX3 and have the same crystal structure as calcium titanate (CaTiO3), where A and B sites accept inorganic cations of various valence and ionic radius. Likewise, halide perovskites in which halogen is substituted at the site of an oxygen anion has been applied to solar cells, showing very excellent properties, and has emerged as a promising material in various fields. Specifically, from a photovoltaic point of view, halide perovskites exhibit beneficial properties for high-performance photovoltaic systems such as a suitable band gap (1.5 – 1.4 eV), high absorption coefficient (104 – 105 cm-1), low exciton binding energy (< 50 meV), and long charge-carrier diffusion length (~175 µm). These excellent properties allowed the power conversion efficiency (PCE) of perovskite solar cells (PSC) to reach values above 25%, which is comparable to that of silicon solar cells studied over a long period of time. However, such rapid increase in PCE has been achieved by optimizing the device structure, the uniform thin film deposition process, and the material composition of the halide perovskite, in addition to its excellent material properties. One of the important factors for uniform thin film deposition was the introduction of mediators that delay the rapid crystallization between organic cations and PbI2 through solvent engineering or intramolecular exchange processes. Another factor was the use and stabilization of a-phase formamidinium lead iodide (FAPbI3) by manipulating the chemical composition of the perovskite. The efficiency was further improved by reducing the grain boundary and surface defect concentration of FAPbI3. In this presentation, I would like to introduce our achievements and ongoing challenges.