Numerical Simulations for In-Depth Analysis of Transmission Line Method Measurements for Photovoltaic Applications—The Influence of the p–n Junction

Abstract

For optimization of solar cell perfomance, the knowledge of the specific contact resistivity between grid finger and emitter is an important component. The contact resistivity is typically characterized by transmission line method (TLM) measurement directly on samples made from complete fabricated solar cells. Large contact spacing on solar cells leads to high measured resistances and thus high voltage drops along the emitter, measuring between several finger distances. This, in turn, imposes a strong load on the p–n junction and can lead to a parasitic current flow over the wafer base itself. The influence of this current flow on the TLM measurement evaluation for typical solar cell parameters is investigated. The 2D simulation of TLM measurements is used to derive handling instructions to improve the contact resistivity measurements. For typical solar cell TLM stripes with emitter sheet resistances of about 150 Ω sq−1 and a reverse p–n junction characteristic similar to rshunt in the range of 10 kΩ cm2, an influence of about 10% or higher ρc evaluation uncertainty is expected.