To further increase the efficiency of thin film solar cells, it is critical to enhance the absorption over the full spectral wavelength range in which solar cells generate electricity. In this letter, we present a fullband absorption enhancement method for n-i-p thin film silicon solar cells based on a Quasi-Crystal Structure (QCS) by superimposing Ag random nanotextures on periodically patterned Micro-Cone Substrates. Both light in-coupling and light trapping abilities are significantly improved thanks to the reduction of front-surface reflection originated from the gradually changed refractive index of preserved micro-cone profile after film deposition and the richer guided mode resonances caused by the QCS. An initial efficiency of 10.4% is obtained for QCS-based hydrogenated amorphous silicon germanium (a-SiGe:H) solar cells, which outperforms the planar (efficiency of 7.5%) and randomly nanotextured (efficiency of 8.7%) counter part by 38.7% and 19.5%, respectively. The QCS can also be duplicated for other thin film photovoltaic devices and provides a new approach for creating high efficiency thin-film solar cells.