CO2 laser annealing for metal halide perovskite solar cells

Abstract

This thesis focuses on the use of CO2 laser with lower photon-energy in the mid-infrared (MIR) range for all the annealing steps contained in perovskite solar cell fabrication. All CO2 laser annealing were performed in the ambient and all cell demonstrations using CO2 laser annealing in this thesis were reported for the first time. Key findings of this thesis include: 1.Laser power is critical to α-FAPbI3 phase formation, without driving out volatile organics from the perovskite nor increasing PbI2 defects. Champion power conversion efficiency (PCE) of 21.8% achieved (without additional additives for perovskite bulk and surface passivations) was the highest for a laser annealed single-junction perovskite solar cell at the time. 2.COMSOL Multiphysics simulations of macroscopic and localised temperature profiles during laser annealing unveiled highly effective laser power absorption and cooling by the perovskite film, especially when compared to Me-4PACz, thereby lowering substrate temperature experienced compared to hot-plate annealing. 3.All laser annealed (HTL and perovskite) wide bandgap (1.80 eV) perovskite solar cell achieving a champion VOC of 1.35 V and a PCE of 19.8%, highest for reported perovskite solar cells with the same bandgap at the time. 4.The first use of CO2 laser for perovskite-OPV tandem solar cells. The laser annealed PM6:Y6 OPV champion cell produced a PCE of 16.8%, highest for a laser annealed OPV cell at the time. The champion perovskite-OPV tandem produced a PCE of 24.0%, comparable to the state-of-the-art. This thesis demonstrates the promising prospects of laser annealing offering time savings and localised heating advantage for temperature-sensitive substrates.