Low Short-circuit Current Density Research Articles

Properties of indium-tin-oxide (ITO)/silicon heterojunction solar cells by thick-film techniques

Solar cells of indium-tin-oxide (ITO)/Si have been fabricated by conventional thick film printing methods onto Si substrates. In this structure the ITO thick film acts not only as a conducting surface layer than forms the SIS junction but also as an antireflective coating. Electrical and optical measurements have shown that the ITO film is reasonably conductive (with a sheet resistance of 300 ω/□) and highly transparent in the visible region. Thick films from pastes of silver and aluminium have been found to be compatible and form ohmic metallic contacts. Typical values obtained for the ITO cells are an open circuit voltage of 0.50 V, a short circuit current density of 0.70 mA/cm 2, a fill-factor of 0.45 and an efficiency of 0.20% under a stimulated illumination of 80 mW/cm 2. The effeciency values are lower than those obtained in thin film ITO solar cells. It is thought that the thickness of the interfacial oxide layer was the main reason for the low short-circuit current density and efficiency. Further work is necessary for the optimization of the devices.

Dendritic Growth of Silicon Thin Films on Alumina Ceramic and Their Application to Solar Cells

Polycrystalline silicon films on alumina ceramic are recrystallized under normal freezing conditions. A multi-layered structure containing borosilicate glass and titanium layers is successfully used to prevent molten silicon films from agglomeration. The films obtained are dendritic and of mm size. Chemical etching reveals tilt boundaries, linear and dot-like defects in addition to grain boundaries. The thin film solar cells fabricated on the recrystallized silicon by successive deposition of p and n+ layers show photovoltaic conversion efficiencies of up to 2.6% at a fill factor of 0.67 under an AMI simulator. From the spectral response curves of the cells, the electron diffusion length of the p-type active layers is calculated to be 1 µm and causes a low short circuit current density of 9.8 mA/cm2.