On the Correlation between Light-Induced Degradation and Minority Carrier Traps in Boron-Doped Czochralski Silicon

Abstract

Boron-doped Czochralski grown silicon wafers dominate the photovoltaic market. Light-induced degradation of these wafers is one of the most significant roadblocks for high-efficiency solar cells. Despite a very large number of publications on this topic, only a few studies have directly investigated the precursor of the defect responsible for this degradation. In this study, using the photoconductance decay measurement method, we identify the precursor of the defect responsible for light-induced degradation. By comparing the photoconductance decay of samples in the different states, we observe the presence of a minority carrier trap in the annealed state which is not present after degradation. Trap annihilation shows a clear anticorrelation with the generation of the recombination active boron-oxygen defect, as determined from minority carrier lifetime measurements. Furthermore, it is concluded that a model based on a single-level trap cannot explain the doping-dependent measurements, meaning that the detected trap has two or more energy levels.

Indium‐Doped Silicon for Solar Cells—Light‐Induced Degradation and Deep‐Level Traps

“…[14,15] In Cz-Si:B, this defect has been argued to be the precursor of the light-induced degradation (LID) defect, which is responsible for the reduction in the lifetime and efficiency of the silicon solar cells. [14,16,17] It can be observed that the boron-doped Cz-Si and indiumdoped samples (In-3) with almost similar doping concentrations of about (4.0-4.5) Â 10 15 cm À3 have a similar trap concentration in the range of (3.0-3.5) Â 10 13 cm À3 . It should be noted that the trap concentration values are derived using the equation:…”

“…During prolonged injection of minority carriers, the B s O 2 complex transforms to a configuration with a shallow acceptor level and enhanced recombination activity. [ 14,16,17 ] This transformation results in a reduction of the minority carrier lifetime in boron‐doped Cz‐Si; i.e., it causes the BO LID of silicon solar cells. [ 14,16,17 ]…”

“…[ 14,16,17 ] This transformation results in a reduction of the minority carrier lifetime in boron‐doped Cz‐Si; i.e., it causes the BO LID of silicon solar cells. [ 14,16,17 ]…”

“…[14,15] During prolonged injection of minority carriers, the B s O 2 complex transforms to a configuration with a shallow acceptor level and enhanced recombination activity. [14,16,17] This transformation results in a reduction of the minority carrier lifetime in boron-doped Cz-Si; i.e., it causes the BO LID of silicon solar cells. [14,16,17] The limited and controversial results on LID in In-doped Si crystals, which are briefly described previously, do not allow a complete explanation for the origin of the observed controversies and an understanding of the defect reactions occurring upon light soaking in Si:In.…”

“…[14,16,17] This transformation results in a reduction of the minority carrier lifetime in boron-doped Cz-Si; i.e., it causes the BO LID of silicon solar cells. [14,16,17] The limited and controversial results on LID in In-doped Si crystals, which are briefly described previously, do not allow a complete explanation for the origin of the observed controversies and an understanding of the defect reactions occurring upon light soaking in Si:In. The authors of the studies in which the LID effects in In-doped Si were reported suggested that the lifetime degradation after light soaking is related to the charge carrier capture and emission by a complex consisting of substitutional In atom and an interstitial silicon atom (In Si -Si i ).…”