About the origin of low wafer performance and crystal defect generation on seed-cast growth of industrial mono-like silicon ingots

Abstract

The era of the seed-cast grown monocrystalline-based silicon ingots is coming. Mono-like, pseudomono or quasimono wafers are product labels that can be nowadays found in the market, as a critical innovation for the photovoltaic industry. They integrate some of the most favorable features of the conventional silicon substrates for solar cells, so far, such as the high solar cell efficiency offered by the monocrystalline Czochralski-Si (Cz-Si) wafers and the lower cost, high productivity and full square-shape that characterize the well-known multicrystalline casting growth method. Nevertheless, this innovative crystal growth approach still faces a number of mass scale problems that need to be resolved, in order to gain a deep, 100% reliable and worldwide market: (i) extended defects formation during the growth process; (ii) optimization of the seed recycling; and (iii) parts of the ingots giving low solar cells performance, which directly affect the production costs and yield of this approach. Therefore, this paper presents a series of casting crystal growth experiments and characterization studies from ingots, wafers and cells manufactured in an industrial approach, showing the main sources of crystal defect formation, impurity enrichment and potential consequences at solar cell level. The previously mentioned technological drawbacks are directly addressed, proposing industrial actions to pave the way of this new wafer technology to high efficiency solar cells.

Building intuition of iron evolution during solar cell processing through analysis of different process models

“…The first 2D Model consists of heterogeneously distributed dislocations and no grain boundaries, representing mono-like [52][53][54][55][56][57][58][59] and epitaxial silicon [60][61][62][63]. The second 2D Model adds a grain boundary to the dislocations, simulating conventional multicrystalline silicon (mc-Si).…”

Mono-like silicon ingots grown on low angle misoriented seeds: Defect characterization by synchrotron X-ray diffraction imaging

“…However, undesirable defects such as sub-grain boundaries and dislocations can occur, at the seed/solidified silicon interface and preferentially at the junctions of the seeds, and extend to the whole ingot during the growth process, having a serious impact on the final solar cell efficiency [4][5][6][7][8][9]. Some research has already been performed aiming to investigate the origin of these kinds of defects.…”

Effect of Small‐Angle Grain Boundary on the Mechanical Properties in Direct Silicon Bonded Wafer

“…In the photovoltaic industry, improved crystal growth techniques as casting quasi‐mono crystalline silicon, and high performance multi‐crystalline silicon have been developed in the recent years. However, the characterized defects of multi‐crystalline still cannot be eliminated …”