Abstract
Fullerene intercalation between the side chains of conjugated polymers has a detrimental impact on both charge separation and charge transport processes in bulk heterojunction (BHJ) organic photovoltaic cells (OPVs). In situ grazing incidence X‐ray scattering experiments allow to characterize the structure formation, drying kinetics, and intercalation in blends of phenyl‐c61‐butyric acid methyl ester (PC60BM) and poly(2,5‐bis(3‐tetradecylthiophen‐2‐yl)thieno[3,2‐b]thiophene) named (pBTTT‐C14) from their 1,2‐orthodichlorobenzene (oDCB) solutions with different volume fractions of dodecanoic acid methyl ester (Me12) as a solvent additive. The structure formation process during evaporation of the solvent:additive mixture can be described by five periods, which are correlated to a multistep contraction of the lamellar stacking of the bimolecular crystals. The onset of crystallization is delayed by increasing the additive volume fraction in the coating solution leading to a promoted crystallinity. A conclusive picture of fullerene intercalation and additive‐tuned structural evolution during the drying of thin films of the polymer:fullerene BHJ blends will be presented.
Highlights
Fullerene intercalation between the side chains of conjugated polymers has a polymer electron donor and an electrondetrimental impact on both charge separation and charge transport processes in bulk heterojunction (BHJ) organic photovoltaic cells (OPVs)
A conclusive picture of fullerene interface so they can be split into fullerene intercalation and additive-tuned structural evolution during the drying of thin films of the polymer:fullerene BHJ blends will be presented
We present in situ studies of the structure evolution of 1:1 pBTTT-C14:PC60BM blends processed with Me12 as an additive
Summary
OPV BHJ film morphology evolves over a series of periods during its formation upon drying from dilute solutions.[47]. Based on the aforementioned discussion, we can propose the following model of the additive-tuned structure formation from solution for intercalating blends: Period 1: Due to its higher vapor pressure, the solvent oDCB evaporates more rapidly than the Me12 additive, resulting in an increased solubility limit of pBTTT-C14 and PC60BM in the mixture. This period ends with reaching the critical concentration of pBTTT-C14 in the oDCB:Me12 mixture as evidenced by the earliest observation of polymer crystallization. Period 5: By the complete removal of Me12, the final film morphology is reached
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