Impact of silicon quantum dot super lattice and quantum well structure as intermediate layer on p-i-n silicon solar cells

The photovoltaic effect of the silicon (Si)/silicon carbide (SiC) quantum dot super lattice (QDSL) and multi-quantum well (QW) strucutres is presented based on numerical simulation and experimental studies. The QDSL and QW structures act as an intermediate layer in a p-i-n Si solar cell. The QDSL consists of a stack of four 4-nm Si nano disks and 2-nm SiC barrier layers embedded in a SiC matrix fabricated with a top-down etching process. The Si nano disks were observed with bright field-scanning transmission electron microscopy. The simulation results based on the 3D finite element method confirmed that the quantum effect on the band structure for the QDSL and QW structures was different and had different effects on solar cell operation. The effect of vertical wave-function coupling to form a miniband in the QDSL was observed based on the solar-cell performance, showing a dramatic photovoltaic response in generating a high photocurrent density J_sc of 29.24 mA/cm², open circuit voltage V_oc of 0.51 V, fill factor FF of 0.74, and efficiency η of 11.07% with respect to a i-QW solar cell with J_sc of 25.27 mA/cm², V_oc of 0.49 V, FF of 0.69, and η of 8.61% and an i-Si solar cell with J_sc of 27.63 mA/cm², V_oc of 0.55 V, FF of 0.61, and η of 10.00%. A wide range of photo-carrier transports by the QD arrays in the QDSL solar cell is possible in the internal quantum efficiency spectra with respect to the internal quantum efficiency of the i-QW solar cell.