Packing Morphologies of Cyanoacrylic Group-Containing Conjugated Molecules on the Surface of TiO2 and Their Effects on the Molecular Orientation of P3HT in Organic Solar Cells：A Study of Molecular Dynamics Simulations
Date Issued
2011
Date
2011
Author(s)
Hsia, Tai-Li
Abstract
We employ the all-atom molecular dynamic simulation and the theoretical calculation to study the different thiophene ring numbers of dye (W1、W2、W3) and change the ring type on molecular chain (W4).The characteristic of their packing orientation may affect the conformation and the adsorption orientation of P3HT. Among the packing morphologies of these dyes, we found that the π-π interaction between the chains become strong when the numbers of ring increase. Parallel displaced and T-shaped stacking are the major geometry among packing orientation of thiophene rings. In this study, the simulation of 50% grafting density is closer to real experiment, so we can compare the experiment and the simulation system. In the 50% grafted density, the arrangement of dyes is sparse and the interaction between chains is small due to the dyes are partial aggregation, so the rings can maintain a better coplanarity and therefore provide a good conjugation system to enable electronic effective delivery; and from the simulation result, we can find the W3 system have the best coplanarity of all the system. In the W4 system, The coplanarity of molecular chain is worse due to the benzothiadiazole ring, so the current density is not as higher as W3 dye system, but the band gap will be reduced because of the molecular chain added D/A system to make the VOC increase. Therefore, the IPCE of W4 system is the highest one of all the systems. When placed the P3HT into the dye system, it’s easier to insert in the dye-layer surface due to the ring numbers increased of dye. Our simulations indicate that P3HT is closer to titanium dioxide substrate, this result lead to electron-hole pair recombination; In order to improve this phenomenon, we raise the grafting density of dyes, however, P3HT is difficult to insert into the dye-layer at higher grafting density cause the long distance between P3HT and dye-layer. The coplanarity of chain is also poor due to high grafting density,so we attempted to reduce the alkyl side chain length of P3HT to improve the charge transfer ability. According to above metion, PT (Polythiophene) was used to adsorb on the high grafting density surface because there exit no alkyl side chain. We found that PT is not only easier to close dye –layer, but PT maintains a coplanar structure. Therefore the ability of charge transfer between polymer and dye-layer were better.
The present result represents when reducing the side chain length of P3AT(poly 3-alkyl thiophene) will promote the coplanarity of the main chain and provide a route to transfer charge.
Subjects
interfacial modification
organic solar cell
dye
molecular dynamics
Type
thesis
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