Dear Gaurav Gupta ,

I think the best mixing ratio between the donors and acceptors molecules is 1: 1 where they hug each other. In this way every generated exciton generated in a donor molecule will find a dissociating acceptor molecules. In this way the dissociation efficiency of the excitons will be one.

In case of fullerene acceptors where the acceptor molecule has low absorption coefficient, this means that half the molecules in the volume will be ineffective absorbers. This problem can be solved partly by increasing the ratio of donor to acceptor molecules to absorb more radiation in the same volume provided that the dissociation efficiency is kept one. Theoretically the ratio must be =

(exciton length of about 20 nm / donor molecule length ) :1

In case of nonfullerene acceptors absorbing efficiently the solar radiation the best ratio will be 1:1.

This issue is discussed in the paper at the link: Conference Paper Generic Analytical Models for Organic and Perovskite Solar Cells

I extended the concept in this post.

It is important to see what are the factors affecting the ratio between the donors and acceptors.

Best wishes

Dear Gaurav Gupta ,

I think the best mixing ratio between the donors and acceptors molecules is 1: 1 where they hug each other. In this way every generated exciton generated in a donor molecule will find a dissociating acceptor molecules. In this way the dissociation efficiency of the excitons will be one.

In case of fullerene acceptors where the acceptor molecule has low absorption coefficient, this means that half the molecules in the volume will be ineffective absorbers. This problem can be solved partly by increasing the ratio of donor to acceptor molecules to absorb more radiation in the same volume provided that the dissociation efficiency is kept one. Theoretically the ratio must be =

(exciton length of about 20 nm / donor molecule length ) :1

In case of nonfullerene acceptors absorbing efficiently the solar radiation the best ratio will be 1:1.

This issue is discussed in the paper at the link: Conference Paper Generic Analytical Models for Organic and Perovskite Solar Cells

I extended the concept in this post.

It is important to see what are the factors affecting the ratio between the donors and acceptors.

Best wishes

Dear Gaurav Gupta,

The ratio of donor to acceptor could be slightly varied according to their molecular weight. You could use molar to do some calculation to work out the exciton formation. As an experimentist, it would be much easier to use mass concentrations. For the example of P3HT:PCBM organic solar cells, the optimised ratio of donor-acceptor is 2:1 to 1:1 which very much depends on the molecular weight of polymer. The concentrations could be varied from 20 mg/ml to 60mg/ml. The way you could do is to make solutions of donor and acceptor, separately. Then mixing their solutions according to the ratio. In this way, you could easily optimise the device performance according to the different conditions. Hope it helps.

U can optimize, do little variations in ratio compare the results.