ANNEALING OF POLYCRYSTALLINE THIN FILM SILICON SOLAR CELLS IN WATER VAPOUR AT SUB-ATMOSPHERIC PRESSURES

Peter Pikna,Vlastimil Píč,Vítězslav Benda,Antonín Fejfar

doi:10.14311/ap.2014.54.0341

Abstract

Thin film polycrystalline silicon (poly-Si) solar cells were annealed in water vapour at pressures below atmospheric pressure. PN junction of the sample was contacted by measuring probes directly in the pressure chamber filled with steam during passivation. Suns-VOC method and a Lock-in detector were used to monitor an effect of water vapour to VOC of the solar cell during whole passivation process (in-situ). Tested temperature of the sample (55°C – 110°C) was constant during the procedure. Open-circuit voltage of a solar cell at these temperatures is lower than at room temperature. Nevertheless, voltage response of the solar cell to the light flash used during Suns-VOC measurements was good observable. Temperature dependences for multicrystalline wafer-based and polycrystalline thin film solar cells were measured and compared. While no significant improvement of thin film poly-Si solar cell parameters by annealing in water vapour at under-atmospheric pressures was observed up to now, in-situ observation proved required sensitivity to changing VOC at elevated temperatures during the process.

Highlights

The efficiency of a solar cell is directly influenced by the semiconductor material that is used
The higher the VOC, the lower the concentration of defects [3]. This key parameter was measured at light intensity 1000 W/m2 = 1 SUN for the Suns-VOC method and at the light intensity of a white LED determined only approximately to be around 1000 W/m2 for the Lock-in detector
A comparison between the effective alternating part of VOC measured by a Lock-in detector and a direct signal measured by the Suns-VOC method purged of parasitic DC signals was performed on the basis of the following recalculation, using VOC measured at room temperature

Summary

Introduction

The efficiency of a solar cell is directly influenced by the semiconductor material that is used. Plasma hydrogenation is usually used for passivation, i.e., to reduce the electrical activity of recombination centres, e.g., grain boundaries, impurities and crystallographic defects in silicon [1,2,3,4,5]. This relatively expensive passivation procedure could be replaced by a cheaper alternative — passivation in water vapour [6,7,8]

Experimental

Suns-VOC method

Lock-in detector

Results and discussions

Conclusions