Contact and Bulk Resistivity Screening for Advanced Crystalline Silicon Solar Cell Concepts by an Economical and Reliable Transfer Length Measurement Method Based on Laser Micro-Patterning

Abstract

Herein, test structures for transfer length measurements (TLMs) are prepared by means of a femtosecond laser micro-machining process for quick and easy measurements of contact resistance and bulk resistivity in thin-film multilayer stacks for advanced high-efficiency silicon solar cells. In particular, silicon heterostructure layer systems composed of tin-doped indium oxide (ITO)/n-doped amorphous silicon (a-Si) on crystalline silicon (c-Si) substrates are used. To study the reliability of this novel laser-based TLM test structure preparation method, measured data from laser structured TLM patterns are compared with conventional structures based on micro-lithography. For small TLM test structures with contact distances between 100 and 1000 μm, the results suggest a significant dependence of the measured contact resistance values on the size of the laser prepared structures. This may be attributed to redeposited material during the laser ablation procedure at the flanks of the contact pads and insufficient mesa structuring. However, the laser and lithography-based preparation methods yield comparable results when larger structures (contact distances between 200 and 2200 μm) are implemented. Herein, size effects can be neglected. For both methods, the specific contact resistance values of ITO/n-doped a-Si/c-Si heterostructures are calculated from 8 to 45 mΩ cm2 for various samples from the same batch.