1,8-Diiodooctane as the Processing Additive to Improve the Efficiency of P3HT:PC<SUB>61</SUB>BM Solar Cells

Abstract

Controlling the blend morphology is critical for achieving high power conversion efficiency in polymer/fullerene bulk heterojunction (BHJ) photovoltaic devices. As a simple and effective method to control morphology, adding processing additives has been widely applied in the organic BHJ solar cells. In this paper, we demonstrate that adding 1,8-diiodooctane as a processing additives is an effective method to improve the morphology and the efficiency of bulk heterojunctions (BHJ) solar cells based on the regioregular poly(3-hexylthiophene) (P3HT) and a soluble fullerene derivative ([6,6]-phenyl C61-butyric acid methyl ester, PC61BM). We investigated the unique way in which the 1,8-diiodooctane plays the rule to enhance the performance of solar cells according to different morphology and crystallinity of active layers prepared with and without the additive. The morphology is studied with atomic force microscopy (AFM) and Grazing Incidence X-ray Diffraction (GIXRD). We also find a balance between a large interfacial area for exciton dissociation and continuous pathways for carrier transportation when the additive is used.

Effect of additive length and chemistry on the morphology of blends of conjugated thiophenes and fullerene derivative acceptor molecules

“…We think that the lack of attractive end “F” bead and fewer number of weakly attractive “E” beads makes E1 unique, where instead of improving backbone alignment, E1 serves to deter backbone–backbone orientational order. Experiments with P3HT:PCBM blends and DIO or alkanethiol additives similarly show an increase in P3HT crystallinity in ternary blends with additives compared with binary oligomer–acceptor blends . In agreement, our simulation results show that additives increase backbone positional and orientational order compared with the case in the absence of additives, but interestingly, this high order is maintained even for ternary blends with larger additives, E3, that do not have attractive end groups.…”

Impact of Donor–Acceptor Interaction and Solvent Additive on the Vertical Composition Distribution of Bulk Heterojunction Polymer Solar Cells

“…29 Fan et al and Zusan et al reported that the solvent additives that induced the morphology could largely decide the performance of polymer:fullerene-based organic solar cells due to the balance between a large interfacial area for exciton dissociation and continuous pathways for carrier transportation. 15,30 The aforementioned reports are indeed helpful for mediating the vertical component distribution. However, most of the studies primarily focus on solutionprocessing parameters and device engineering, while few works are available on components itself, especially on finding relationships between the vertical component distribution and electron donors, electron acceptors, and donor−acceptor Flory−Huggins interaction parameter χ, an indication of miscibility, repulsion, and phase separation between the donor and acceptor components.…”

“…BHJ film solution-processing parameters, including solvent-vapor, thermal annealing, mix solvents, and solvent additives, which have been shown to promote the molecule movement in films, may drive the components to segregate at the bottom or top of the BHJ films. − For example, Ruderer et al reported that the vertical separation occurs during spin coating and annealing, depending on the solvent used . Fan et al and Zusan et al reported that the solvent additives that induced the morphology could largely decide the performance of polymer:fullerene-based organic solar cells due to the balance between a large interfacial area for exciton dissociation and continuous pathways for carrier transportation. , The aforementioned reports are indeed helpful for mediating the vertical component distribution. However, most of the studies primarily focus on solution-processing parameters and device engineering, while few works are available on components itself, especially on finding relationships between the vertical component distribution and electron donors, electron acceptors, and donor–acceptor Flory–Huggins interaction parameter χ, an indication of miscibility, repulsion, and phase separation between the donor and acceptor components.…”