When the same fabrication steps are carried out on rigid substrates (glass) efficiencies usually seem 1-2% better than on the flexible substrates (PET, PEN), even when the device structure is identical otherwise and the same fabrication steps are followed. What might be some reasons for this discrepancy?
Hi George,
Try to check two things before comparing different substrate:
1. Surface resistivity
2. Transmittance
Generally, ITO coated glass have good transmittance as compare to PET or PEN based substrate with same surface resistivity. However, the substrate with high transmittance will allow large no. of photon as compare to the substrate with low transmittance, therefore, affects the overall device performance.
This is one of the reason, hope this information will work for you.
The practical answer is surface morphology. The most efficient perovskite solar cells utilize large grains to maximize carrier mobility; however, on a flexible substrate, those grains must be small as to not shatter when being flexed.
Also, electrical contact adhesion is challenging in rigid solar cells and is only magnified in flexible ones.
Several reasons can be attributed for that :)
1. Decrease in carrier mobility due to bending.
2. Contact resistance increases behind the back contact.
3. Due to scattering of carriers due to bending.
4. Producing more defects while bending or lowering the grain boundary (reduces the minority carrier life time hence the collection probability of minority carriers)
5. Transmittance as Rahul explained
You may have to study the particular pervoskite material and relevant literature can help to find the appropriate cause :)
I hope that will help you for more clear understanding! Good Luck :)
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