PhD byNatltjilalie Pre
alrissler (firstname.lastname@example.org), Germany (PPRE 2012/14)
PvcomB in Berlin, part of Helmholtz-Zentrum Berlin
Single junction thin film silicon solar cells on glass substrates with conversion efficiencies of up to 13 % can be achieved by melting the 5 – 20 µm thick silicon absorbers with a heat source such as a laser or an electron beam. The silicon converts into highly crystalline material which leads to solar cells with open circuit voltages of 618 mV for p-doped absorbers and 657 mV for n-doped absorbers. A dielectric interlayer (IL) stack based on amorphous silicon nitride (a-SiNx:H), amorphous silicon oxide (a-SiOx:H) and/or amorphous silicon oxynitride (a-SiOxNy:H) is sandwiched between the glass substrate and the silicon absorber to prevent de-wetting of the absorber during the crystallization process. In addition, the IL stack enhances light in-coupling into the absorber as well as passivation of the buried absorber surface.
In the framework of the PhD thesis the IL stack is developed based on plasma-enhanced chemical vapor deposition (PECVD) and physical vapor deposition (PVD) techniques. The influence of the IL stack composition on the absorbers morphological and electric properties of corresponding solar cells is investigated. By employing capacitance-voltage (C-V) measurements, the passivation quality in terms of the fixed charge density in the IL as well as the defect state density at the IL/absorber interface is analyzed and put into relation with corresponding solar cell performances.
Another aspect of the PhD thesis is about the effect of a high-temperature hydrogen plasma treatment on the solar cells. This treatment is known to reduce defects in the silicon and at the silicon surface. The open circuit voltage in LPC-Si solar cells is significantly increased through the treatment. However, the microscopic origin of the improvement is not clear yet. Within the PhD thesis a model is developed, which describes the effect of the high-temperature hydrogen plasma treatment on the absorber quality.