Anamaria Moldovan

Combined Ozone/HF/HCI Based Cleaning and Adjusted Emitter Etch-Back for Silicon Solar Cells

RCA cleaning in multiple variations is widely used in photovoltaic production lines for high efficiency solar cells. These commonly peroxide based cleaning procedures are effective, but suffering from large chemical consumption and waste generation. A substitution of hydrogen peroxide by ozone in cleaning solutions is not realized yet for PV devices despite its high oxidation potential and facility advantages. The very high potential of ozone cleaning has been shown in various microelectronic applications [1-7]. Dissolved ozone in HF/HCl solution gives the option of cleaning by combined silicon etching and oxidizing as well as complexing metal contaminations due to F- and Cl-.

Passivation of solar cell emitters using aluminum nitride

Layers of hydrogenated aluminum nitride have proven excellent passivation properties on lowly doped silicon. Effective surface recombination velocities below 8 cm/s have been reached due to a very low interface defect density. In this work, the passivation of highly doped silicon is studied by measuring the emitter saturation current of boron as well as phosphorous emitters. It is shown that hydrogenation is a prerequisite for reaching effective passivation. Emitter saturation current densities of around 100 fA/cm2 are presented for highly doped p+-type and n+-type silicon allowing maximal open circuit voltages of ~680 mV for silicon solar cells.

Surface Charge and Interface State Density on Silicon Substrates after Ozone Based Wet-Chemical Oxidation and Hydrogen-Termination

For more than 20 years, the application of ozone dissolved in pure deionised water (DIW-O3) has been investigated for wafer-cleaning and resist stripping applications in the semiconductor industry [, , ]. To reduce chemical consumption and disposal costs as well as to improve cleaning efficiency, DIW-O3 is used in semiconductor wet cleaning processes as an alternative to traditional sulphuric acid peroxide (H2SO4/H2O2) [] and RCA [] cleans. Silicon solar cell fabrication includes multiple wet cleaning steps involving large amounts of chemicals. In Si substrate manufacturing the wet-chemical oxidation of substrate surface is used mainly for three purposes: (i) the removal of surface contamination and surface micro-roughness by different cleaning and smoothing procedures in H2O2 containing solutions (RCA I and RCA II) [5], in H2SO4/H2O2 [4], (ii) the preparation of hydrophilic surfaces for subsequent layer deposition [,] and (iii) the fabrication of thin oxide layers []. Chemical consumption could be reduced by replacing some of these chemicals with a mixture of pure deionised water with dissolved ozone for cleaning and surface conditioning. The kinetics of wet-chemical oxidation in DIW-O3 were recently investigated by ellipsometrical measurements of oxide thicknesses (ox>) [3,6,7], by SPV-measurements [7,], by contact angle measurements as well as by quasi-steady-state photo conductance (QSSPC) measurements [7].

Surface Contamination of Silicon Wafer after Acidic Texturisation

The acidic texture bath that is commonly used in crystalline silicon solar cell manufacturing is a mixture of HF/HNO3/H2O [. While the influences of metal contamination on silicon wafer surfaces as well as several cleaning methods were intensively investigated in the previous 30 years [ the effect of metal contaminations in texturisation baths has not yet been studied intensively. There are two categories of contaminations: