Materials Science and Engineering Ph.D. Dissertation

Abstract

With better physical properties and stability than polycrystalline, single-crystal perovskite is an ideal material for achieving high-performance perovskite solar cells. However, the inferior efficiency of single-crystal perovskite solar cells suggests a particular strategy is crucial to raise the efficiency baseline similar to polycrystalline solar cells. We dedicate this dissertation to offering systematic approaches for achieving high-performance micron thick single-crystal perovskite solar cells and X-ray detectors.

In the first part of this dissertation, we explored the possibility of enhancing single-crystal perovskite solar cells by improving the surface quality of the crystal. Even though single-crystal has low defect density, the surface defect of single-crystal is known to be poorer or comparable with polycrystalline film. By utilizing the additives method, we provided a universal approach on passivating micron thick single-crystal perovskite capable of enhancing efficiency to 21.9% based on V_oc improvement from non-passivated crystal.

In the second part, we investigated single-crystal perovskite composition by tuning the bandgap perovskite close to the Shockley-Queisser limit. During crystal growth, a modulated temperature ramp was utilized to produce MA-free FAPbI3-based perovskite single crystals. By employing a state-of-the-art composition, the single-crystal perovskite solar cells can achieve a record efficiency of 24.3%. We displayed superior device stability of single-crystal perovskite solar cells under thermal stress and light illumination.

In the last part of this dissertation, we implemented a direct adaptation of MA-free single-crystal perovskite solar cells upon self-powered X-ray photovoltaic devices. The adequate thickness of an X-ray detector comparable to diffusion length properties is necessary to realize a high-performance X-ray detector. By increasing the thickness of single-crystal perovskite solar cells using the spacer, we obtained 100 μm thick crystal with efficiency of 22.1% PCE and showcased the direct adaptation as X-ray photovoltaic devices with sensitivity and detection limit of 420 μC Gy^-1 cm^-2 and 526 nGy/s, respectively, at 0 V bias. We further elucidate the improved sensitivity of X-ray photovoltaic devices by increasing the thickness to 400 μm.

With these systematic approaches, we anticipate accelerating the advancement of single-crystal perovskite toward achieving high-performance solar cells and X-ray detectors.