Contacting a single nanometer-sized pinhole in the interfacial oxide of a poly-silicon on oxide (POLO) solar cell junction

The electrical current through poly-Si on oxide (POLO) solar cells is mediated by tunneling and by nanometer-sized pinholes in the interfacial oxide. To distinguish the two processes, a POLO junction with a measured pinhole density of 1 × 107 cm−2 is contacted by different contact areas ranging from 1 μm2 to 2.5 × 105 μm2, and the temperature-dependent current–voltage curves are measured for the different devices. Model regressions to the measured curves, their temperature dependence, and the quantized value of contact resistances indicate average numbers of pinholes per device corresponding to the expected pinhole density. For the small contacts, the different transport processes can be studied separately, which facilitates further improvements in respect to the present-day POLO junctions. Single-pinhole transport is found for one of the contacts with an area of 1 μm2. Random telegraph noise observed for this device in the current–voltage characteristics shows a high sensitivity to single charges

Introducing pinhole magnification by selective etching: Application to poly-Si on ultra-thin silicon oxide films

Carrier selective junctions formed by polycrystalline silicon (poly-Si) on ultra-thin silicon oxide films are currently in the spotlight of silicon photovoltaics. We develop a simple method using selective etching and conventional optical microscopy to determine the pinhole density in interfacial oxide films of poly-Si on oxide (POLO)-junctions with excellent electrical properties. We characterize the selective etching of poly-Si versus ultra-thin silicon oxide. We use test structures with deliberately patterned openings and 3 nm thin oxide films to check the feasibility of magnification by undercutting the interfacial oxide. With the successful proof of our concept we introduce a new method to access the density of nanometer-size pinholes in POLO-junctions with excellent passivation properties