With the increase in the development of new
technologies in photovoltaics, it is equally
important to understand the vulnerabilities of
such technologies, as it is expected to have a
consistently good performance and ability to
maintain trust among the consumers. Since
eventually, the energy generated by the solar
plants matters more than simply the installed
capacity, it is important to pay attention to the
long term reliability of PV power plants.
Novel techniques have been implemented in significant fabrication steps like texturization, emitter diffusion, emitter passivation and an anti-reflection coating, edge-isolation, screen printing and co-firing. Let's have a look at some of these techniques at a deeper level on how it is carried out.
Innovative Texturization Method:
A novel single-step low-cost saw damage removal (SDR) solution of potassium
hydroxide (KOH) has been
prepared. In essence, sodium hypochlorite (NaOCl) has been introduced, followed by
pyramidal texturing
using KOH, potassium silicate (K2
SiO3
) and isopropyl alcohol (IPA) solution resulting in a weighted average
reflectance of 13.4% for mono-crystalline wafers.
Better Diffusion and Passivation techniques:
Improved diffusion recipes using POCl3
, resulting in better uniformity in sheet resistance has been
incorporated. Further, the sheet resistance has been increased from 65 ohm/sq. to 90
ohm/ sq. resulting in
better passivation and improvement in quantum efficiency at a lower wavelength range
of 300-450 nm. The
emitter surface passivation quality has been improved using a low-cost,
low-temperature (40°C), non-acidic
and safe chemical oxide passivation process (named as NCPRE-oxide) was grown with
the help of sodium
hypochlorite solution. In comparison with other existing oxide growth or deposition
processes such as dry
thermal oxide, this process has the thermal budget, easy waste disposal, and single
component nature,
which makes it viable for industrial-scale implementation.
Uniform and Non-absorbing Anti-Reflection Coating:
Deposition recipes for anti-reflection coating have been optimized, resulting in
non-absorbing and a
uniform thickness (<5%) and refractive index (<1%). Uniformity was improved by
increasing pressure, and reduction in absorption was achieved by decreasing
silane -ammonia ratio.
Improved screen printing and co-firing techniques:
With the availability of new and advanced screen printers, NCPRE can now print
fingers on the top side of
solar cells with 45 micro-meter widths maintaining a high aspect ratio. This has
resulted in the reduction of
current loss due to metal shading without compromising the electrical
properties. Further, a recently
installed industrial-grade belt furnace has been used for co-firing of front and
back metal contacts which
have improved the fill factor from 80.1% to 81.2%.
