Many report says thicker active blend film will be good for obtaining decent PCE? However, in our laboratory environment, thinner active film (~ 90 to 100 nm for both P3HT:PCBM/ICBA) is showing best results. (Please note we dont have sophiscated glove box system). Request your best suggestions for obtaining improved PCE.
have you published your results.
I think 100nm is the minimum requirement for the thickness but I will always get good results with 150-200nm layers.
Actually active layer needs to be 100-300nm thick for absorbing solar spectrum. If you decrease the layer thickness absorbance decreases and this will effect the efficiency of the OSC.
Probably you manage to obtain the best performances in terms of FF by using a thinner film and this help to rise the efficiency. By increasing the thickness, you should increase the current and lose something in FF.
Thanks for the reply. Well said, there is a trade-off between Jsc and FF always.
Please also comment on the importance of using glove box?. Will it influence the overall PCE of BHJ solar cells? We perform all the steps in open-air atmosphere only.
Dear Arumugam, Thanks for the clarification. We always prepare active blend solution (P3HT : ICBA) in open-air atmosphere by stirring it in a hotplate and proceed device fabrication. Which will oxidize fastly, polymer or fullerene one?..So far, P3HT:ICBA based cells in our lab, witnessed only a max PCE of 3.53% only. Should we perform photoactive deposition only inside nitrogen/argon atmosphere? How about only stir the active solution inside N environment and depositing active layer in open-air atmosphere?
Hi Sai, you should perform photo-active layer deposition inside the glove box if your activity is addressed to high conversion efficiency. I usually spray this layer in air and I know that I cannot reach the same efficiency of layers sprayed inside a glove box. Anyway Sasikumar opens a good discussion. I know that it is possible to weight the polymer and the fullerene outside the glove-box without problems, so does the fullerene oxidation only take place when it is dissolved in the solvent (and not in the solid state)?
I worked with P3HT:PCBM mixture before. The thickness and the viscosity of the solution play an important role in the final PCE. Decreasing the active layer thickness improve the FF and the JSC and hence the the PCE. I did the preparation outside the glove box.
Shaimaa,. Could you please share the maximum PCE parameters witnessed for your P3HT PCBM based cell. Please also inform the thickness and any specific stirring conditions you had followed.
Hi! You're trying to fabricate a ternary blend. The thickness of the film depends on the polymer. P3HT is a crystaline polymer and is efficient at 150-200 nm to a binary with PCBM. Other amorphous polymers (e.g. PCDTBT) are efficient at ~100 nm. ICBA plays a bridging role between P3HT and PCBM, thus providing more routes for charge transfer at the donor/acceptor (D/A) interface. Meanwhile, when the ICBA content is much smaller than the PCBM content, the morphology of the ternary blend active layer is similar to that of P3HT:PCBM. So, try a thickness of ~150-200 nm.
Dear Minas, Thank you for the detailed response. Please also, inform the best electrode material (cathode) for bulk heterojunction PSCs. Currently, we use Al (cathode) or ZnO/Al electrode. I noticed many researchers are using LiF/Al. Request your best suggestions.
Dear Sai-Anand. We use TiOx as electron transport layer, proposed by Heeger (sol-gel chemistry) and Al as cathode electrode. We encapsulate the cell after the fabrication in order to retard the oxidation.
You can be adviced by
http://pubs.rsc.org/en/Content/ArticleLanding/2014/CC/c3cc49004a#!divAbstract
about the fabrication process.
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