Regular Article

Optimized amorphous silicon nitride layers for the front side passivation of c-Si PERC solar cells

¹ Fraunhofer Institute for Solar Energy Systems ISE, Heidenhofstraße 2, 79110 Freiburg, Germany
² Department of Physics, Faculty of Science, Menoufia University, Menoufia, Egypt

^* e-mail: asmaa.mohamed.okasha.mohamed.okasha@ise.fraunhofer.de

Received: 23 August 2019
Received in final form: 6 March 2020
Accepted: 3 April 2020
Published online: 29 May 2020

Abstract

Plasma-enhanced chemical vapour deposition (PECVD) SiN_x is the typical choice as anti-reflection coating (ARC) for Silicon based solar cells. However, there still exists a room for improvement in passivation quality of SiN_x while maintaining good optics for the front side of a solar cell. In this paper, we studied in detail the optical and electrical properties of SiN_x layers by varying the chamber pressure and substrate temperature in an industrially used inline PECVD tool. Both the optical as well as electrical properties of SiN_x layers were found to be significantly influenced by the chamber pressure and substrate temperature. A trade-off between excellent optics and low surface recombination is observed with an increase in chamber pressure, whereas higher substrate temperature generally led to better passivation quality. The Si-H bond density, which is expected to directly influence the quality of surface passivation, increased at high pressure and at low substrate temperature. Based on our investigations, a good compromise between optics and surface passivation is struck to prepare optimized SiN_x layers and apply them as passivation layers for the front side of passivated emitter and rear cell (PERC) solar cells. The best solar cells show high short-circuit current density (j_SC) of 39.9 mA/cm² corresponding to the SiN_x layers with low parasitic absorption, good antireflection property, and excellent passivation of the surface and bulk silicon. The current-voltage (I-V) results are found to be in agreement with internal quantum efficiency (IQE) measurements of the solar cells.