You can find an extensive study in Adv. Mater. 2010, 22, 4355–4358.

Pre-thermal annealing at 150 ° C is needed to reduce the surface roughness

Dear Konios, thanks for the reply. How about the active layer thickness influence on the photovoltaic performance? (I had tried fabricating thinner active films of thickness about ~100 to ~125 nm but without pre-thermal annealing, however witnessed only a poor PCE of 1%). Is there any specific procedure available for blend (P3HT:ICBA) solution preparation?

From a wuick view in the literature, I saw that the best results are for a 125nm P3HT:ICBA active layer. In our experiments, we use oDCB as the blend solvent, leaving the blend under stirring at 75C overnight before using it.

Dear Konios, we also use DCB as a processing solvent. Could you please share the P3HT:ICBA active layer reported paper ? :)

Take a look at

J. AM. CHEM. SOC. 2010, 132, 1377–1382 (180-220nm)

Adv. Energy Mater. 2014, DOI: 10.1002/aenm.201301777

http://nova.newcastle.edu.au/vital/access/manager/Repository/uon:13593?f0=sm_subject%3A%22organic%22 (100nm)

Thank you for sharing useful references :)

What are the reasons for drop in open-circuit voltage (Voc) ? For P3HT:ICBA based BHJ solar cells, the minimum Voc should be around ~ 0.80 V, but in our fabrication, we only witnessed a 0.62 V (max).. Is this because of the active layer thickness?

Hi Sai,

Here are a couple of things I have noticed.

1. If you use DCB then try solvent annealing(slow drying) the films. As far as I have seen active layer thickness 150-200 nm thick films are mostly used and have given the best results (Check Yang Yang and Yongfang Li's papers). Also annealing temperature and thickness are dependent. Maybe I can explain this in detail if you need more info.

2. If you use CB as solvent then thermal annealing is critical to get high Jsc. However Voc will decrease a little bit (From 0.9V to 0.82V). But I have always preferred to use CB instead of DCB as it eliminates the use of solvent annealing.

3. P3HT:PCBM and P3HT:ICBA have some differences when it comes to morphology. ICBA has higher solubility and mixes with amorphous P3HT to a much greater extent than PCBM. So it might not follow the same processing conditions. However when you make cells its always good to also fabricate P3HT:PCBM cells along with it to check if you get nominal efficiency with P3HT:PCBM. I have gotten above 4% for P3HT:PCBM and almost 6% with P3HT:ICBA and I will be publishing on those results soon.

Dear Venkat, Thanks for sharing useful comments.

1) Next time, will try fabricating thicker active layer films (slow drying inside glass petri side, followed by thermal annealing). Please explain the influence of annealing temperature and thickness on photovoltaic performance.

2) I had also seen co-solvent (CB and DCB) paper showing a slightly reduced Voc (for inverted structure). I have attached herewith for your kind reference. Also, CB is a low-cost solvent, relatively.

3) I will follow your suggestions during device fabrication. Is there any specific procedure for blend (P3HT:ICBA) preparation ? I follow like this : 17mg/ml P3HT stirred at 100C for 5 hrs and then blending with 17mg ICBA stirred at 50C overnight. Please comment on this.

Please inform about the article once its published (would like to read and cite).

Sai :)

Hi Sai,

1. I believe when you coat your films thin then the annealing temperature should be low. I feel this is because thinner films have less disorder (See http://pubs.acs.org/doi/abs/10.1021/nn404172m ) and hence annealing will tend to give coarser phase segregation. I have seen in my case that when I coat the films thin (~50nm) the color of it comes out purple rather than orange as observed for 150nm thick films. However if your goal is get is to get respectable efficiency with DCB then try coating them at 600-800 rpm with acceleration of 150rpm/s and total time 30-40s. Then perform solvent annealing for atleast 30 mins and thermal annealing at 140 or 150C for 10 mins.

2. I also have used inverted structure and what I have found is annealing above 150C is crucial for films casted with CB solvent. Additionally when I use solvent additive such as Nitrobenzene or DIO then Jsc improves significantly. 2-3 volume percent is the optimal concentration for additive as observed by me for P3HT:ICBA blend.

3. Normally I mix both P3HT and ICBA together in 1:1 blend and stir them for 16-18 hours at 80C before spin coating. The ICBA that we have is from Solvene. Where did you purchase your ICBA from?

I can send you my MRS presentation on comparison of P3HT PCBM and P3HT:ICBA if you want. Send me your email id.

Swami

Dear Swami, thank you for the detailed response.

1) Next time, I will try fabricating reasonably thicker active films ( ~ 150 to 200 nm), and perform solvent annealing (inside glass petri dish) followed by thermal annealing (150C for 10 min).

2) Nice observation, additives can greatly alter PV performance. please provide if there are related publication (from yours)

3) I will follow the same as yours and try fabricating cells

Please send the MRS presentation to [email protected].

Sai :)

3) I forgot to mention this, IC60BA was purchased from Lumtec, Taiwan :).