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Optimization of Belt Furnace Anneal to Reduce Light and Elevated Temperature Induced Degradation of Effective Carrier Lifetime of P‐Type Multicrystalline Silicon Wafers
Author(s) -
Sharma Romika,
Aberle Armin G.,
Li Joel B.
Publication year - 2018
Publication title -
solar rrl
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 2.544
H-Index - 37
ISSN - 2367-198X
DOI - 10.1002/solr.201800070
Subject(s) - materials science , wafer , silicon , carrier lifetime , degradation (telecommunications) , annealing (glass) , optoelectronics , thermal , charge carrier , dark current , solar cell , composite material , electronic engineering , physics , meteorology , engineering , photodetector
Light and elevated temperature induced degradation (LeTID) of the effective charge carrier lifetime significantly lowers the efficiency of multicrystalline silicon (mc‐Si) solar cells and is a major challenge currently faced by the silicon photovoltaic industry. Optimization of the temperature profile used in the rapid thermal anneal (RTA) step of the metallization line has been found to significantly reduce LeTID of mc‐Si solar cells. Hence, the authors experimentally study the impacts of varying the RTA process parameters on the LeTID behavior of mc‐Si lifetime samples. It is shown that a low peak temperature, slow ramp‐up rate (slow belt speed) reduce LeTID in mc‐Si lifetime samples. Also, subsequent dark anneal at a moderate temperature (≈300–550 °C) further reduces LeTID. Samples already subjected to LeTID conditions also benefit from the post‐degradation dark anneal. The recovered effective carrier lifetime of the degraded samples dark annealed at 550 °C is even higher than the post‐firing effective carrier lifetime value. The defect state achieved post‐dark anneal at 550 °C is stable for the studied period of ≈60 h, unlike the well‐known case of low‐temperature dark anneals (<200 °C) where samples degrade again when subjected to LeTID conditions. The authors believe that the optimized conditions identified in this work can be applied to mass‐produced mc‐Si solar cells.