Silicon quantum dots in photovoltaic devices: Device fabrication, characterization and comparison of materials

Silicon nanocrystals (Si NCs) embedded in Si-based dielectrics provide a Si-based high band gap material (1.7 eV) and enable the construction of all-crystalline Si tandem solar cells. However, Si nanocrystal formation involves high-temperature annealing which deteriorates the properties of any previously established selective contacts. The inter-diffusion of dopants during high-temperature annealing alters Si NC formation and limits the built-in voltage. Furthermore, most devices presented so far also involve electrically active bulk Si and therefore do not allow a clear separation of the observed photovoltaic effect of the quantum dot layer from that of the bulk Si substrate. A membrane route is presented for quantum dot based p-i-n solar cells to overcome these limitations. In this approach, the formation of both selective contacts is carried out after high-temperature annealing and therefore not affected by the latter. P-i-n solar cells are investigated with Si NCs embedded in silicon carbide in the intrinsic region. Open-circuit voltages of up to 370 mV are shown for the NC layer. An optical model of the device is presented for improving the cell current. Finally device failure due to damaged insulation layers is analysed by electron beam induced current measurements