Enhanced broadband spectral response and energy conversion efficiency for hetero-junction solar cells with graded-sized Si quantum dots/SiC multilayers

In order to circumvent the narrow spectral response of Si quantum dots (Si QDs)-based solar cells, a novel hetero-junction cell structure containing graded-sized QDs-based multilayers was proposed. The size of Si QDs varies from 8 nm to 2 nm which corresponds with the bandgap from 1.2 eV to 2.1 eV. The graded-sized Si QDs-based hetero-junction cell exhibits an enhanced spectral response in a wavelength range from 400 nm to 1200 nm, which is obviously improved compared with that of conventional Si QDs-based cells. Furthermore, by combining the graded-sized Si QDs multilayers with Si nanowire arrays, a Si QDs/Si NWs hetero-junction solar cell was fabricated and the corresponding power conversion efficiency can be as high as 12.80%, due to the significant spectral loss suppression and optical absorption enhancement by forming nano-patterned light trapping structures.