Methylammonium Lead Iodide thin lms grown by Pulsed Laser Deposition for Photodetector Applications

Abstract

This thesis studies the fabrication and characterization of Methylammonium Lead Iodide perovskite thin films for photodetector applications. Unlike, any other perovskite halide material, Methylammonium Lead Iodide perovskite has long range balanced electron and hole transportation lengths. A major challenge is to use such materials to grow fine quality thin films. We tried to grow these perovskite thin films by the Pulsed laser deposition (PLD) technique, which is well known and successful in areas such as metal oxide-based complex perovskite systems. The unique ability to transfer from the bulk to a film with original Stoichiometry is the main strength of this technique. The first chapter provides a brief overview of the halide Perovskites and their properties such as optoelectronic properties, Ferroelectric property and thermal conductivity. In the second chapter, we describe the Pulsed laser deposition (PLD) technique used for the synthesis of the thin films. The invention of PLD technique has helped the fabrication of high-quality uniform thin films over a large area on the substrate. Understanding the pros/cons of PLD technique helps us in identifying the novelty of the thesis work. The second chapter also describes material growth techniques and all the characterization techniques that provide foundation for the entire thesis. In the third chapter, we describe the application of the CH3NH3PbI3 thin films grown by pulsed laser deposition for photodetection applications. With this method, we obtained good perovskite films coverage on fluorine-doped tin oxide coated substrates and observed well developed grains. The films showed no sign of degradation over several months of testing. We investigated the surface morphology and surface roughness of the films. We carried out a study on the solar and infrared photodetection of CH3NH3PbI3 thin films. In the fourth chapter, we describe the effect of change in annealing temperature and annealing time by keeping the thin film fabrication parameters constant. Annealing temperature was varied from 100 ◦C to150 ◦C including room temperature sample. The annealing time which was maintained for 10 min. We investigated structural and optical characterizations for all the samples (with different annealing temperature). Further, we carried out near-infrared photodetection of the CH3NH3PbI3 based thin films using an infrared lamp (IR) of 808 nm source at 0V. In each case the photo response was found to be stable with time. We annealed this sample with different annealing time 10 min, 30 min,50 min 70 min and 90 mins. At the end we have observed that the photo responsivity of the samples was high for a combination of annealing temperature of 150◦ C for 90 mins. In the chapter 5, we used TiO2 as an electron transport layer to enhance the photo response of the device. The TiO2 layer was grown by same technique. The fluorine doped tin oxide glass was used as substrate on that we grown TiO2, and then CH3NH3PbI3. The structural, morphology, cross section and optical properties of the films were studied. The photo response showed higher than previous samples. We also introduced one more layer Spiro-OMeTAD as a hole transport layer, while the idea behind this was to improve the photoresponsivity of the device FTO/TiO2/CH3NH3PbI3/Spiro-OMeTAD. Here again, studies were done in terms of cross-section and morphology of the film. We carried out similar electrical measurements. After introducing the hole transport layer, the photo responsivity increased. Here we compared the photoresponse parameters of both devices FTO/TiO2/CH3NH3PbI3 and FTO/TiO2/CH3NH3PbI3/Spiro-OMeTAD. In the Chapter 6, The thesis concludes with an overall summary of this work and with some future predictions based on the device structures.