For recombination and high electrical conductivity emitters. [43] Mandelkorn

For
the greater development of the world’s renewable energy system, there is plenty
of research is going on around the world. Increasing the solar cell efficiency
by light trapping of the solar cell is now becomes a matter of great interest
researchers. As diffusion process is one of the most important processes for
fabricating solar cell, many researchers are interested in diffusion technique.
Forming an emitter in solar-grade silicon wafer in different ways by varying
the diffusion time and temperature is now a quit interesting research topic for
researchers.

Han
et.al. fabricated a monocrystalline silicon solar cell. The doping temperature
was 8500C. They found that the reflectance for bare and textured
silicon wafer is 31.1% and 14.1%. The efficiency of their solar cell was 16.7%.
42

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Hongzhao
et.al studied the impact of deposition gas flow ratio, drive in temperature and
duration, drive in O2­ flow rate, and thermal oxidation temperature, on emitter
formation and electrical performance. POCl3 diffusion can be broken down into
two steps. 1.Deposition of PSG layer. 2.a subsequent drive in to move the
phosphor-silicate deeper into the silicon. In their study they identified the
previous parameters and given an overall guideline to demonstrate how emitter
formation could be controlled to fulfill different device application, ensuring
glow recombination and high electrical conductivity emitters. 43

Mandelkorn
et.al. fabricated phosphorus diffused solar cell. Solar cells having the sheet
resistance of 10 ohm/sq, high long-wavelength collection efficiency, and
efficiencies above 10% were fabricated by diffusion at 9750C.
Diffusions carried out at 8750C for 0.5 to 1-hour periods resulted
in cells having high short and long wavelength collection efficiency. Gridded
contacts applied to the cells to minimize the sheet resistance raised the
efficiencies of the cells to values above 10%. The high short- wavelength
collection efficiency of the 8750C diffused cells results in
increased radiation resistance of these cells. Cells having efficiencies above
10% were made from 13 ohm-cm material and found to have higher radiation
resistance than cells made from 1 ohm-cm material. Low junction reverse
currents and contact resistances of approximately 0.2 ohms have also been
achieved in their research. 44

Ghembaza
et.al presented a theoretical model on study of the effects of the temperature,
diffusion time, surface concentration and doping profile on the crystalline
silicon solar cell performances by using new parameters. They performed an
established phosphorus diffusion model to show that practical diffusion times
and temperatures can control the junction depth as well as the formed emitter
quality. Their output data delineate direction for solar cells efficiency
improvement through a focus on the exact SiO2 barrier layer
thickness and phosphorus profile management. They improved the emitter
efficiency and solar cell performance by 2.78%. 45

Asrafusjaman
et.al. fabricated monocrystalline silicon solar cell at Bangladesh Atomic
Energy Commission. They used 150*150 mm2 monocrystalline silicon
wafer with 200 ?m thickness. The reflectance of raw wafer and textured wafer
was also measured. The difference of surface reflectance at wavelength 975nm is
30.4%. They diffused the wafer with liquid POCl3 in the diffusion
chamber. They carried out their diffusion process at 8500 C – 9000C.
The sheet resistance for the diffused wafer is 0.88 ?-cm which was measured by
the four-point probe. They found the efficiency of their solar cell is about
6.89%. 46

Shirazi
et.al. showed the influence of the phosphorus precipitation during at the
PSG/Si interface during the pre-deposition phase on the passivation quality of
the corresponding emitter. In the second step, they used the results to create
emitters with a reduced density of phosphorus precipitates. In a last step, the
optimized emitter structure was transferred to screen-printed solar cell
processes, whereby efficiencies up to 19.4%. 
They also showed that the PSG can not only serve as a diffusion source
of phosphorus, but also as a source for diffusion of O into Si. This fact may
also be responsible for the additional precipitate formation in the Si
substrate. The increase in the POCl­3-N­2 gas flow during pre-deposition
clearly leads to an increased P precipitate formation on the emitter surface
and in the emitter volume, which was confirmed by comparing ECV with SIMS
measurements. 47

Akand
et. al. fabricated a monocrystalline silicon solar cell with 200 ?m
thick silicon wafer. They fabricated the emitter on the silicon surface at
temperature 8750C on the diffusion chamber. When the phosphosilicate
layer was formed at 8500C they remove the PSG layer by chemical
treatment of HF solution. After doing RTA they found the efficiency of their
solar cell is 7%. 48