Master thesis subjects

Subject 1: Porous silicon rear reflectors for very thin silicon solar cells

A very interesting route towards cheaper solar electricity is through reduced material consumption by using very thin wafers. Unfortunately, transmission-related losses become increasingly important as the wafer thickness is reduced. In this thesis, graded and multilayered films of porous silicon will be modeled and fabricated using electrochemical methods. Thereafter, the optical properties of these films will be characterized using spectral reflectance and transmittance measurements, as well as spectral ellipsommetry.

Supervisors: Josefine Selj
Project:  ISP

Subject 2: Losses in designer solar cells – the impact of varying colour on solar cell efficiency

Architects and designers often request solar cells of varying colours. In this thesis, the efficiency reduction from varying the colour of real solar cells through introducing new anti-reflex films will be assessed. Both single-layer and multi-layer anti-reflex films will be investigated. Firstly, the optical properties of the films will be modeled and their impact on real solar cells estimated. Thereafter, single-layer and multi-layer films will be fabricated by plasma enhanced chemical vapour deposition (PECVD) and characterized using spectral reflectance and spectral ellipsommetry measurements.

Supervisors:  Sean Erik Foss
Project:  FME/ISP

Subject 3: Simulation of metallization patterns

The metal grid on the front surface of a solar cell is designed in order to avoid excessive losses due to reflected light off the contact fingers (shading) while maintaining a low series resistance in the solar cell. In this thesis, metallization patterns for various solar cell technologies will be simulated and series resistance and shading losses estimated. Thereafter, screens will be designed and metal patterns characterized using electrical and structural characterization techniques.

Supervisor:  Junjie Zhu
Project:  FME

Subject 4: Defects in zinc oxide

Transparent conductive oxide (TCO) materials enable a variety of new, high efficiency solar cell designs. However, the performance of such materials is strongly dependent on their microstructure. In this thesis, thin films of the TCO material zinc oxide will be deposited and characterized. Process parameters will be modified in order to enhance the formation of specific defect states.

Supervisors:  Smagul Karazhanov
Project:  ISP

Subject 5: Development of metal hydrides as solar cell materials

IFE has a very exciting project going on with development of metal hydrides as possible solar cell materials for the future. Metal hydrides can make a basis for cheap solar cells based on abundant elements. The focus of this task will be magnesium nickel hydride, which is a semiconducting material which is promising because it has a perfect band gap for collection of solar light.

Supervisor:  Trygve Mongstad
Project:  ISP

Subject 6: Thermal oxidation passivation for Si-based, high efficiency solar cells

Surface passivation is an important issue in semiconductor device fabrication. For solar
cell fabrication, low surface recombination is one of the basic requisites to reach high
conversion efficiency. Several deposited dielectric materials can provide good surface
passivation, such as a-SiN_x:H, a-Si:H, SiO_x:H and Al_xO_y. However, many high
efficiency solar cells today are employing thermal oxidation to obtain excellent surface
passivation with low surface recombination. In this thesis, thermal oxidation processes
will be investigated with the aim of establishing a good, long term stable surface
passivation on Si wafers. Selected post-treatments will also be investigated. Key tools in this thesis are minority carrier life-time measurements for quantifying surface
recombination velocities, ellipsometry to determine thin film thicknesses and C-V
measurement to investigate the electronic properties of the Si/SiO₂ interface.

Supervisor:  Junjie Zhu / Sean Erik Foss

Subject 7: Laser doping for selective emitter formation

Selective emitters with a heavily-doped contact area underneath the metallized region
and a lightly-doped emitter area between front fingers have already shown the
advantage of increasing solar conversion efficiency. Several approaches, such as ion
implantation, two step diffusion with mask and inkjet printing have been employed to
achieve selective high doping. Laser doping is a promising alternative due to the
possibilities of local formation of highly doped emitters with a high throughput. In this thesis, laser doping processes will be established. Characterization of the doped surfaces will be performed using sheet resistivity measurements, PL/EL imaging and SIMS. As a final goal, prototype solar cells with a selective emitter created with a laser doping process will be prepared.

Supervisor:  Junjie Zhu / Sean Erik Foss