The technological flux of solar-cell fabrication on multicrystalline silicon substrate (Si-mc) contains the next steps:
1. Thermal oxidation bywater vapors at T = 1100 ◦C in order to create a masking layer which was etched on the back-side of the wafers.
2. To improve the back-side wafer contacts these were highly doped with boron by prediffusion from solid source B+ at T = 1050 ◦C/N2 [8]. The prediffused layer characteristics are: the deep xj = 0.6m and V/I = 4–5. In the next step, an oxide layer with thickness of 6200Å was created by wet oxidation at
T = 1000 ◦C, which was used as a masking layer in the next technological step. During thermal oxidation boron diffusion in the wafers was also performed.
3. The windows opening in the diffusion oxide (the active area of the cell) was performed by photolithographic process using the mask M1 (Fig. 3) and the silicon oxide has been etched using a NH4F:HF = 6:1 solution with an etching rate of 1000Å/min. In the active cell area the silicon surface was texturized with the solu-
tion HNO3:HF:CH3COOH= 25:1:10, at room temperature (Fig. 4a,b) and with solution KOH25% at 80 ◦C(Fig. 4c) [9]. Texturization results in an increased surface roughness, enabling a longer optical path for light entering into the cell, thus increasing light absorption and solar-cell efficiency [10].
4. The emitter n+ region from solar-cell active area was realized by the prediffusion from POCl3 liquid source at T = 1050 ◦C. The prediffusion layer characteristics are: xj = 0.6m and V/I = 1.5–2.5. V/I was measured with a four point probe. The formed phosphoric pentoxide creates a layer of phosphorus–silica glass (SiO2 + P) on the wafer, from which phosphorus atoms will prediffuse into the upper part of the wafer. After prediffusion completion the remaining
phosphorus–silica–glass layer is removed by etching with fluoric acid (HF:H2O= 1:10, t = 15 s). The next step is the phosphor diffusion at T = 975 ◦C/water vapors for 10min. During diffusion process an non-reflexive layer with thickness of 1200Å was growth [11].
5. In this thin oxide layer the contact window was then opened by photolithographic technique, using themaskM2 (Fig. 5). The contact windows with dimensions of 60mare opened over the texturized surface by using acid or KOH.
6. The metallic contacts of solar cell [12] were realized by aluminium thin film (1m thick) deposition by high vacuum thermal evaporation on both, front- and back-sides of the wafer.
Besides, in the contact zone the metallization mask M3 (Fig. 6) was used on the top side of the wafers (Fig. 7). The width of the metallic line is 80m. The aluminium treatment was performing by sintering at T = 450 ◦C, for 30min in forming gas (3% H2 in N2).
7. The last step consists of device testing and solar-cell structures separation. The obtained solar cell is presented in Fig. 7.

От: The low cost multicrystalline silicon solar cells, Materials Science and Engineering B 165 (2009) 190–193

*ба бъ** дир* бля
св. св. електрон и неговите протони
чукча-читател