Increasing the thickness of ETL in photovoltaic device lowers the Fill factor and efficiency as well. However in one of the devices with only different HTL than first device, the efficiency decreases as expected w.r.t. ETL thickness, however, the FF initially shows an abrupt fall then starts rising again with ETL thickness.
ETL, absorber, contact material and other processing conditions are same for both devices. The only difference is HTL for the two devices are different.
How could this difference affect the behavior of FF.
Dear Khursheed
The energy level of HTL can affect the performance of an OPVs due to the hole injection barrier with other contact layers and also transport mobility. Other optical properties of a HTL such as absorption can affect the efficiency too.
FF alone isn't a good indication of cell quality. A cell can have a high FF and and eff of say 1% while another cell can have a FF of 70% and an eff of 20%. What are Voc and Ioc doing as you increase ETL thickness? I guess that one of them is dropping and causing a spurious increase in FF. Don't worry about FF until your cells are showing at least 5% eff preferably a LOT more. It isn't a good indicator of quality when the quality is low - only when it is high.
Thanks Dear Dr. Tony Maine.
I agreed and Efficiencies achieved were of the order of 17 % and 15% with two different HTLs. Since the product VocxFFxIsc is numerically equal to the conversion efficiency.
My question was basically how it could be different, the behavior of the FF when only HTL is changed. In one device, it decreases monotonically w.r.t. the thickness while shows initially an abrupt fall then starts increasing again.
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