Synthesis and layering of Si quantum dots/SiO2 composite films for third generation solar cells

• Laser synthesis in weighable amount of 4 nm silicon quantum dots
• Dispersion and layering of Si dots in SiO2 matrix (sol–gel + spin coating)
• Thermal diffusion doping by boron and phosphorus inserted during sol–gel process.
• Films with 2.6 1018 cm− 3 isolated dots with homogeneous distribution
• 1.8 eV measured bandgap with resistivity as low as 3.1 10− 3 Ω cm

4 nm silicon quantum dots (Si-QDs) produced by laser pyrolysis have been embedded in a SiO2 matrix using sol–gel process. The nanocomposite layers exhibit promising properties for third generation solar cell application. High resolution transmission electron microscopy observations show that the particles are well dispersed in the matrix, and separated by a short distance (< 1 nm). The bandgap of the layer is found equal to the bandgap of the individual 4 nm Si-QDs. The electrical conductivity was found to increase with increasing annealing temperature, Si-QD concentration and dopant concentration in the sol. The main advantage of this process is the possibility to reach a very high Si-QD density inside the film whilst still ensuring a strong quantum confinement in the particles. This latter point is critical for a future possible use of Si-QDs in high efficiency photovoltaic devices.