A. Boronat

Sub-Bandgap External Quantum Efficiency in Ti Implanted Si Heterojunction with Intrinsic Thin Layer Cells

In this work we present the manufacturing processes and results obtained from the characterization of heterojunction with intrinsic thin layer solar cells that include a heavily Ti ion implanted Si absorbing layer. The cells exhibit external circuit photocurrent at photon energies well below the Si bandgap. We discuss the origin of this below-bandgap photocurrent and the modifications in the hydrogenated amorphous intrinsic Si layer thickness to increase the open-circuit voltage.

Analysis of GaAs-Ti thin films deposited by sputtering onto c-Si and GaAs

Some sputtering processes of GaAs and Ti onto glass, c-Si and c-GaAs substrates have been carried out in order to obtain thin films as candidates to be intermediate band photovoltaic materials. This work presents first results concerning the optical and structural properties of the different deposited thin films.

Ohmic contacts fabricated on moderately doped p-type GaAs by sputtering deposition and a laser-firing process

A novel approach is used to achieve ohmic contacts on moderately doped p-type GaAs substrates. A laser-firing process is used instead of the conventional annealing step. The morphology of the crater created by the laser-firing process and the electrical response of the metal–semiconductor contact are characterized.

Study of GaAs(Ti) thin films as candidates for IB solar cells manufacturing

Thin films of GaAs(Ti) have been deposited by sputtering on glass and n_GaAs substrates under different process conditions. Optical characteristics of these samples have been analyzed to study the potential of this material in intermediate Band solar cell manufacturing.

HIT intermediate-band solar cells with self-assembled colloidal quantum dots and metal nanoparticles

The particular opto-electronic properties of chemically synthesized colloidal nanoparticles can be promising for functional materials, as those required for high efficient photovoltaic (PV) devices. In particular, appropriately-designed semiconductor colloids (quantum dots, QDs) can potentially allow sub-bandgap current generation in intermediate-band solar cells; while metal nanoparticles (MNPs) sustaining surface plasmons can provide both near and far-field light trapping to further boost the generated power. However, the incorporation of colloidal particles in inorganic PV materials is not trivial, therefore their implementation has so far been restricted to organic/polymeric based solar cells. In this work, PbS colloidal QDs have been incorporated in the intrinsic a-Si:H layer of HIT (substrate/a-Si:H hetero-junction) test structures. Both c-Si and GaAs substrates have been used, and in some cases colloidal Au NPs have also been included. The obtained devices are meant as probes to verify the feasibility of incorporating foreign nanoparticles in a cell structure and not as potentially efficient solar cells. Despite the radical novelties incorporated, the devices behaved similarly to the references, thus proving the compatibility of the proposed materials and processes.

Influence of hydrogen on the optical absorption response of GaAs(Ti) films deposited by R.F. sputtering

In the present work we have investigated the optical absorption behavior of GaAs(Ti) films deposited by r.f sputtering technique under different H2 partial pressures. In previous work we have already demonstrated the feasibility to obtain GaAs films with high dose of Ti, which we refer to as GaAs(Ti). Any absorption peak, which could be related with the presence of an intermediate band, has been identified. The low Etauc parameter together with a broad Urbach tail of the films make us to suspect that the possible presence of an absorption peak could be hidden. The incorporation of H2 on sputtered GaAs films have demonstrated before a shift of the Etauc parameter to higher values and a reduction of the Urbach tail.

Optical measurements on GaAs(Ti) thin films sputtered on GaAs

Some sputtering processes of GaAs(Ti) onto c-GaAs have been carried out in order to obtain thin films as candidates to be intermediate band photovoltaic materials. This work presents the results obtained in the study of the absorptance, from transmittance and reflectance responses, in samples obtained at different conditions of temperature and power during the sputtering deposition.