Millisecond annealing for advanced doping of dirty-silicon solar cells

Abstract

Cost reduction is the overall goal in the further development of solar cell technologies. Multicrystalline silicon has attracted considerable attention because of its high stability against light soaking. In case of solar grade mc-Si, the rigorous control of metal impurities is desirable for solar cell fabrication. Although ion implantation doping got very recently distinct consideration for doping of monocrystalline solar material, efficient doping of multicrystalline solar material remains the main challenge to reduce costs. The influence of different annealing techniques on the optical and electrical properties of mc-Si solar cells was investigated. Flash lamp annealing (FLA) in the ms-range is demonstrated here as a very promising technique for the emitter formation at an overall low thermal budget. It could be presented that FLA at 1000 °C for 3 ms even without preheating is sufficient to recrystallize implanted silicon. The sheet resistance of FLA samples shows the values of about 50 Ω/sq. Especially, the minority carrier diffusion length for the FLA samples is in the range of 80 μm without surface passivation. This is up to one order of magnitude higher than that observed from rapid thermal annealing or furnace annealing samples. This technology shows great promise to replace the conventional POCl3-doping.

A review of thermal processing in the subsecond range: semiconductors and beyond

“…This method was also applied to SiH 4 [22], and in both cases sub-monolayer growth rates were achieved. Furthermore, FLA was utilized for the nitridation of Si (100) in an NH 3 ambient [23], and was introduced in atomic layer deposition (ALD) as a possibility for in situ annealing. Suchin situ annealing allows the deposition of crystalline films, larger grain sizes, or even the growth of quantum dot structures [24].…”

“…A new solar cell technology with FLA as the key annealing step after doping by ion beam implantation or plasma immersion implantation was developed. FLA was used to simplify the fabrication process of dirty-silicon solar cells and to make it more cost effective [100]. In this case an amorphous doped Si layer was the result of an ion beam phosphorus implantation step that replaced the traditional POCl 3 doping.…”

Realization of conformal doping on multicrystalline silicon solar cells and black silicon solar cells by plasma immersion ion implantation

“…[16,17] RTA with temperature higher than 900 • C redistributes and activates the impurity metal in silicon. [18] High temperature processing that influences the minority carrier diffusion length, since impurities are highly mobile at elevated temperatures. [19] The furnace process at 850 • C increases the lifetime up to 4 µs.…”

Many hamsters: how the EU can enable private firms to provide renewable energy

“…Renewable energy could support many objectives -including energy security, reduced environmental damage, green jobs, green growth and poverty reduction (Edenhofer et al, 2013, p.S13). Solar power research is being carried out in Europe, including Spain (Fernández-Reche et al, 2006), Finland (Hashmi et al, 2011) and Germany (Prucnal et al, 2012). EU support for solar power could encourage technological advances, keeping Europe at the forefront of non-polluting energygenerating technology (creating long-term jobs and exporting renewable energy equipment to the rest of the world).…”