Microscale Contact Formation by Laser Enhanced Contact Optimization

Abstract

A technique to improve contacts of solar cells laser enhanced contact optimization (LECO) has been studied in terms of micro scale contact formation at industrial PERC solar cells. High-resolution diagnostics by focused ion beam techniques and scanning electron and transmission electron microscopy indicate the LECO-induced formation of microscopic contacts at the buried interface between the screen-printed silver finger and the silicon wafer. A large quantity of these micro contacts where found exclusively for LECO processed cells. Target preparation and threedimension cross-section investigation reveal an interdiffusion of the Ag and Si material as the underlying root cause for improved local contact resistivity. We propose a descriptive model for local ohmic contact formation maintaining surface passivation.

Short Drying Processes for Silicon Solar Cells

“…[23] The power conversion efficiency is taken as a measure for the overall solar cell performance. After the initial I-V measurements, the solar cells are treated with the LECO process [24][25][26][27][28] and I-V measured again. LECO is a relatively new process that improves underfired silver-silicon contacts to the optimum stage and is, therefore, more and more used in the PV community.…”

Reliability Evaluation of Photovoltaic Modules Fabricated from Treated Solar Cells by Laser‐Enhanced Contact Optimization Process

“…At the same time, the passivation quality was not influenced. [ 5–7 ] A first model of the microscale contact formation was recently presented by Großer et al, [ 17 ] introducing LECO‐induced locally limited current‐fired nanoscale silicide contacts.…”

Laser‐enhanced contact optimization on iTOPCon solar cells

“…The resulting local current flow of several amperes is responsible to significantly reduce the contact resistivity ρ c between semiconductor and metal electrode. 19 That process is repeated throughout the whole wafer area using a R&D tool from CE, significantly decreasing the contact resistivity, hence boosting the FF. The scan time per wafer in our R&D environment is set to 1.6 s and can be easily decreased to 1 s or below, insignificantly decreasing LECO's effectivity.…”

“…The LECO process locally applies a highly intense laser pulse on the front side of the solar cell, which is held at constant reverse voltage of 10 V and more. The resulting local current flow of several amperes is responsible to significantly reduce the contact resistivity ρ c between semiconductor and metal electrode 19 . That process is repeated throughout the whole wafer area using a R&D tool from CE, significantly decreasing the contact resistivity, hence boosting the FF .…”