I want to fabricate bilayer active layer in organic solar cells. I'm using PTB7-Th and PCBM as donor and acceptor in a device structure of ITO/ZnO/Active layer/MoO3/Ag.
Usually in BHJ structure, I made solution of PTB7-Th:PCBM in CB. To fabricate bilayer structure, I made two separate solution : PTB7-Th in CB and PCBM in CB. Firstly, I spin coated PCBM solution on ZnO layer and annealed to dry.
But, how can I spin coat PTB7-Th solution on the top of PCBM layer? As PCBM is soluble in CB. Directly spin coat the PTB7-Th solution, the PCBM layer will be dissolved.
The PTB7-Th and PCBM solutions should be mixed according to either weight ratio or molar ratio to make an active layer. The mixture of donor and acceptor in organic semiconductors for OPVs is essential to obtain efficient solar cells. The separate layers of donor and acceptor have proved that there are very little to form exciton diffusion, thereby very little photocurrent generated which leads to very low power efficiency of an OPV.
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