Recombination Strength of Dislocations in High‐Performance Multicrystalline/Quasi‐Mono Hybrid Wafers During Solar Cell Processing

Abstract

Wafers from a hybrid silicon ingot seeded in part for High Performance Multicrystalline, in part for a quasi‐mono structure, are studied in terms of the effect of gettering and hydrogenation on their final Internal Quantum Efficiency. The wafers are thermally processed in different groups – gettered and hydrogenated. Afterwards, a low temperature heterojunction with intrinsic thin layer cell process is applied to minimize the impact of temperature. Such procedure made it possible to study the effect of different processing steps on dislocation clusters in the material using the Light Beam Induced Current technique with a high spatial resolution. The dislocation densities are measured using automatic image recognition on polished and etched samples. The dislocation recombination strengths are obtained by a correlation of the IQE with the dislocation density according to the Donolato model. Different clusters are compared after different process steps. The results show that for the middle of the ingot, the gettering step can increase the recombination strength of dislocations by one order of magnitude. A subsequent passivation with layers containing hydrogen can lead to a decrease in the recombination strength to levels lower than in ungettered samples.

Impurity control in high performance multicrystalline silicon

“…RAGB's were also investigated by SIMS, but the enrichment characteristic of dislocation clusters was not found here. Further details of this study are published elsewhere .…”

Recombination activity of grain boundaries in high-performance multicrystalline Si during solar cell processing

“…A detailed description of the seeding structure can be found elsewhere. 8,16 More information about wafer processing and sample preparation can also be found therein, but the basic details are presented below.…”

“…3,7 It was reported that the increased recombination strength of dislocations during solar cell processing can be related to a change in precipitate distribution. 8 In the so-called High Performance Multicrystalline (HPMC) silicon, material grain boundaries are an important part of the structure. Traditionally, grain boundaries were considered as harmful to device performance, and crystal growth processes were optimized to obtain large grains with small grain boundary densities.…”

A Method to Quantify the Collective Impact of Grain Boundaries on the Internal Quantum Efficiency of Multicrystalline Silicon Solar Cells

“…Furthermore, it has been demonstrated that the recombination activity of dislocations can be quantified from the IQE maps. [9][10][11][12][13] For grain boundaries, the approach is typically based on the contrast profile of individual grain boundaries, i.e., the linescan contrast between the current induced by either an electron beam or a light beam at the grain boundary and the background current value. [14][15][16][17][18][19][20] Although such an approach is extremely useful in understanding the behavior of individual grain boundaries, it may be difficult to obtain an overall assessment of the impact of grain boundaries on the performance of the solar cell based on a few isolated grain boundaries.…”