Effect of annealing on silicon heterojunction solar cells with textured ZnO:Al as transparent conductive oxide

A Salomon,L Francke,M Labrune,G Courtois,P Prod’Homme,P Roca I Cabarrocas,C Charpentier

doi:10.1051/epjpv/2012004

Abstract

We report on silicon heterojunction solar cells using textured aluminum doped zinc oxide (ZnO:Al) as a transparent conductive oxide (TCO) instead of flat indium tin oxide. Double side silicon heterojunction solar cell were fabricated by radio frequency plasma enhanced chemical vapor deposition on high life time N-type float zone crystalline silicon wafers. On both sides of these cells we have deposited by radio frequency magnetron sputtering ZnO:Al layers of thickness ranging from 800 nm to 1400 nm. These TCO layers were then textured by dipping the samples in a 0.5% hydrochloric acid. External quantum efficiency as well as I -V under 1 sun illumination measurements showed an increase of the current for the cells using textured ZnO:Al. The cells were then annealed at 150 °C, 175 °C and 200 °C during 30 min in ambient atmosphere and characterized at each annealing step. The results show that annealing has no impact on the open circuit voltage of the devices but that up to a 175 °C it enhances their short circuit current, consistent with an overall enhancement of their spectral response. Our results suggest that ZnO:Al is a promising material to increase the short circuit current (J sc ) while avoiding texturing the c-Si substrate.

Highlights

Double side heterojunction (DHJ) solar cells are photovoltaic components with a high potential for making high conversion efficiency and cost effective devices
Our result show that zinc oxide (ZnO):Al could be used as a transparent conductive oxide (TCO) in DHJ and the texturing of the entire cells by hydrochloric acid (HCl) dip does not alter surface passivation
Even though further optimization is still needed for the short circuit current (Jsc), we could achieve cells with Voc of 690 mV and fill factor (FF) of 76%

Summary

Introduction

Double side heterojunction (DHJ) solar cells are photovoltaic components with a high potential for making high conversion efficiency and cost effective devices. The use of thin amorphous silicon layers for emitter and back surface field (BSF) formation provides high quality surface passivation [2] and high open circuit voltage (Voc) [3]. It makes it possible to manufacture the cells through low temperature processes (200 ◦C) [4]. Such a low thermal budget allows reducing costs and it allows reducing wafer thickness without breakage [5].

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Conclusion