In the first part of this thesis, we discuss the design and fabrication of arrayed waveguide gratings implemented on the Si3N4/SiO2 integration platform. Arrayed waveguide gratings (AWGs) are widely applied in telecommunication systems as multiplexers/demultiplexers and signal routers, as well as in optical sensing, quantum computing and spectroscopy. It is believed to be a promising solution to some major challenges in observational astronomy. Our AWG design and devices are based on 100-nm Si3N4 on SiO2 platform. Three-stigmatic-point (TSP) AWGs are designed and demonstrated to feature flat output image surface, which can be cleaved to apply cross-dispersion optics for astronomical observation. V-shaped and crossover structures have been introduced. A V-shaped structure is based on the structure used in Rsoft while the crossover structure overlaps two free spectral range (FSRs) and shorten the lengths of arrayed waveguides. For a lower resolving power design with V-shaped structure, the peak transmission reaches -1.9 dB and the highest resolving power is around 5,300. For the higher resolving power design with crossover structure, the peak transmission is -2.0 dB and the maximum resolving power goes above 18,000. The performance of all three input channels is very consistent despite prominent side lobes due to larger phase error. The degradation of resolving power within one FSR is only 6%.A cascaded AWG is developed to broaden the FSR without increasing the footprint. The design approach used in the project is a small primary AWG with broad FSR and multiple large secondary AWGs. However, the cascaded AWGs require a flat response for the primary AWG (flat-top AWG) to prevent large losses at the outer channels as well as at the position of the channel cross-points. The design of flat-top primary AWG is based on modifying the power profile along the input aperture and the phase distribution along the output aperture, creating a sinc function as input signal into the output FPR. A three stigmatic point (TSP) AWG is used as the secondary AWG for achieving better cross-dispersion performance. One-top-hat or two-top-hat layouts are utilized in the design. Experimental results demonstrate that the Rowland primary AWG has higher peak transmission but suffer significant loss at the channel cross-points while a flat-top primary AWG features slightly lower peak transmission but has a huge improvement at the channel cross-points, improving significantly in transmission by more than 12 dB experimentally. However, phase errors generate prominent side lobes and deteriorate the crosstalk. A cascaded AWG with a flat-top primary stage shows a flat output response within the passband, but Rowland primary AWG performs better in terms of filtering out unwanted signals outside the passband. In part 2 of this thesis, we present our work on realizing high performance perovskite based solar cells. A FAxMA(1-x)PbI3 perovskite solar cell with a tunable bandgap from 1.59 to 1.50 eV is proposed. A superstrate configuration with an inverted planar structure is adopted. The structure of our FAxMA(1-x)PbI3 perovskite solar cell is FTO glass/PTAA with m-MTDATA/Perovskite/PCBM/Ag. Sequential PTAA doping and solvent-assisted annealing techniques are used to improve the performance of FAxMA(1-x)PbI3 perovskite solar cell. SEM images clearly show that MAPbI3 (x=0) film has the highest degree of crystallinity with an average grain size over 2 m. As the FAI proportion increases, the degree of crystallinity decreases, resulting in smaller grain size. FA0.33MA0.67PbI3 perovskite material is the optimized ratio for single-junction solar cell and the corresponding power conversion efficiency (PCE) is 16.5%, with an open circuit voltage (Voc) of 1.02 V and a short-circuit current (Jsc) of 24.5 mA/cm2. A fill factor (FF) of 66% is extracted and it reflects a lower crystallinity. The external quantum efficiency (EQE) of FA0.33MA0.67PbI3 perovskite solar cell is measured to be above 90% of efficiency over a broad spectral range from 400 to over 600 nm and remains above 80% around 760 nm, and the absorption onset is pushed to 820 nm due to a lower optical bandgap of 1.54 eV. MAPbI3 solar cell with optical bandgap of 1.59 eV is a great fit as the top cell paired with copper indium selenide (CIS) bottom cell with bandgap of 1 eV. A four-terminal perovskite-CIS tandem solar cell is proposed. I-V characteristics and EQE are taken to investigate the performance. The champion cell demonstrates a PCE of 19.5% which improves the optimized single-junction FA0.33MA0.67PbI3 perovskite solar cell by 3%. If a freshly fabricated bottom CIS solar cell was used for tandem solar cell, the overall PCE would be expected to be above 20%.