Abstract

Research over organic perovskites for light harvesting gained the momentum in past decades. Due to the convenient low temperature and uniform deposition over large area these materials are being tested for the vitality in various light harvesting devices such as in solar cells, X-ray detectors, gamma photon captures etc., On meeting the expectation, the power conversion efficiency in these devices peaked above 20% in around four years of research. But the underlying physics in these materials remains a mystery particularly that which concerns the undesirable high dark currents and photo gains when illuminated with X-ray for medical imaging.
In this thesis, the x-ray sensitivity of perovskite photoconductors under different detector operating conditions has been identified. The primary mechanism that regulates the photocurrent and dark current behavior of X-ray imagers based on organic perovskite photoconductors has been identified. Energy level misalignments between different layers of X-ray imagers leading an injective photo-gain has been investigated. The signal spreading due to trapping, k-fluorescence generation and reabsorption, pixel aperture and primary charge interaction with photoconductor has been accounted by calculating the theoretical MTF for different spatial frequency. These imaging performances are also explored by calculating the theoretical Detective Quantum Efficiency (DQE) at zero spatial frequency. Proceeding further, numerical investigation of organic perovskite had also been accounted to visualize the electric field profiles along the thickness of photoconductor. All possible recombination mechanisms and traps are included in the numerical solution of continuity, trap, and Poisson's equations simultaneously. Sensitivity reduction due to repeated exposure (Ghosting) has been investigated. A variation of electric field profile under different exposure levels has been noticed. It becomes evident that significant deviations between the analytical and numerical approaches were noticed under high exposure levels. This is due to the significant variation of electric field profiles under very high exposures. The work in this thesis identifies the important factors such as the need for appropriate blocking contacts for low dark currents, improved carrier transport properties in perovskite films and proper energy level alignment between different layers of photodetector in order to make successful perovskite x-ray detectors.