Studies of Solution Processable InGaP-based Quantum Dots and Perovskite Solar Cells
This dissertation discusses the synthesis and characterization of solution processable photoluminescent quantum dots based upon indium phosphide, and investigations aimed at improving the stability of solution-processed perovskite solar cells. In the first part, methods of synthesizing high quality photoluminescent quantum dots are studied, especially colloidal synthesis methods. A highly confined semiconductor nanostructure, using InGaP as the core and ZnSeS as a graded ternary outer shell was designed and synthesized through a combination of hot-injection and step-wise methods. The synthesized quantum dots were characterized by transmission electron microscopy (TEM), UV-vis absorbance spectroscopy, photoluminescence quantum efficiency (PLQE) measurements, and continuous wavelength (cw) laser-excited and time-resolved photoluminescence spectroscopy. These quantum dots exhibited high PLQE up to ∼ 90% with tunable emission color (spectral widths ranging from 57 nm to 72 nm). The PLQE dropped by less than 20% when the temperature increased from 25 to 145°C. The quantum dots exhibited continuous photoluminescent emission under both pulsed and continuous laser excitation, even at intensities that produce more than one exciton, on average, per quantum dot. In the second part, we studied the solution processed perovskite solar cells (PSCs), focusing on improving the stability of perovskite films and prevention of hysteresis in device current-voltage characteristics. The planar heterojunction PSC was developed with a PCBM layer and a cross linker in the perovskite layer, to obtain more stable and less hysteretic devices. The device and active layer were characterized by scanning electron microscopy (SEM), X-Ray diffraction (XRD), current density-voltage ( J-V ) measurements, and photoluminescence lifetime measurements. The device performance and chemical stability were improved, with the power conversion efficiency (PCE) up to 13.9%. The hysteresis and formation of precipitates were suppressed by addition of a cross-linker to the perovskite layer.