‘Just-Clean-Enough’: Optimization of Wet Chemical Cleaning Processes for Crystalline Silicon Solar Cells

Abstract

Advanced concepts for photovoltaic silicon solar cells, especially high-efficiency n-type solar cells, requires appropriate wet cleaning treatment in order to remove metallic contamination prior to high temperature processes like diffusion and passivation [1]. The cost of the cleaning process should be as low as possible that requires an optimized usage of the chemicals by increasing process tank lifetimes and developing dedicated feed and bleed recipes. The just clean enough concept has been developed to fulfil the needs of PV industry to minimize the consumption of chemicals. When the dominant contamination metal is identified in quality and quantity, a dedicated wet chemical cleaning process can be applied to remove the metal concentration from the semiconductor surface under a specified limit with the minimum volume on cleaning solution. The paper describes how to optimize a dedicated wet cleaning process for prominent metal impurities like Fe, Cu, Cr, Ti, Co and Zn. For each metal an exchange volume is determined to develop a feed and bleed recipe. The accumulation of the metal impurities in the process tank is calculated and process tank lifetimes are predicted.

Efficiency gain in plated bifacial n-type PERT cells by means of a selective emitter approach using selective epitaxy

“…The cleaning is required to remove any impurity or native oxide present on the open silicon surface, which can prevent a selective deposition or unnecessarily degrade the quality of the grown film and therefore its electronic properties. The iPV cleaning we normally use in-house during solar cell processing [47], and which consists of a 2-step sequence based on DIW/O3/HCl and DIW/HF/HCl was also applied here prior to epitaxy. The SEM image of FIG.…”

Impact of Controlled Ni Contamination on Silicon Solar Wafer Material

“…The wafers with the highest Ni surface concentration, of 2 E11 at/cm 2 (from (3000ppb) mixture), are exposed to different wet chemical cleaning solutions to extract the cleaning efficiency to the specific metal. We have tested 1 tank HF/HCl, sequential DIW/O3+HF/HCl, and 1 tank DIW/O3/HF/HCl solution for surface metal impurity removal [10]. After the cleaning step of 3-5min the wafers received the same thermal oxidation as described before.…”