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.

Optimization of ohmic contact on n-type GaAs by screen-printing silver paste

“…where R sh is the sheet resistance of GaAs, and L T stands for the transmission length. 16,17) The relationship between specific contact resistivity r c and transmission length L T is expressed as:…”

Comparison of the Values of Solar Cell Contact Resistivity Measured with the Transmission Line Method (TLM) and the Potential Difference (PD)

“…As numerous studies show [ 8 , 9 , 10 , 11 ], the electrode layer should meet various requirements to ensure the low resistance of the electrode connection zone with the substrate. Of particular importance is the appropriate selection of the material, including the electrode and substrate; the conditions of its production; the shape and size of the electrode and its adhesion to the substrate; and the substrate morphology [ 12 , 13 , 14 ]. The resistivity is understood to be the quantity that characterises the metal–semiconductor junction, considering the area above and below the junction.…”

Ohmic metal/Hg1-xCdxTe (x ≈ 0.3) contacts

“…The metal/semiconductor contact specific resistivity is typically characterized by TLM measurements, which are extensively used in application to different semiconductors (see, e.g. [12,[54][55][56]). The linear transmission line model [12,54] measurements were performed to determine the specific resistance to p-type HgCdTe (x ≈ 0.3) at the temperatures 77 and 300 K. There were used several collections of test structures with dimensions of contact pads with the lengths L = 10-50 µm and the widths W = 500-2700 µm.…”