以粗粒化技術模擬有機小分子太陽能電池在 真空蒸鍍過程中其主動層之結構衍變

Abstract

本論文中運用Gay-Berne力場對有機光電小分子進行粗粒化轉換，用以模擬真空蒸鍍製造小分子太陽能電池主動層的過程，並從得出之結果探討不同分子比例對主動層結構的影響。在真空蒸鍍的系統中分子連續烙下沉積、並且透過與表面分子的交互作用不斷累積成BHJ結構，為了放大形成的結構並拉長模擬的時間，此系統中應用了粗粒化的概念並採用非等向的力場形式進行模擬。三維橢球型的Gay-Berne力場因此被導入系統之中，由Gay-Berne力場描述的分子間作用力主導了分子的運動模式，並間接引導了整體結構的形成。實驗中建立了多組粗粒化分子動力模擬系統，對於不同系統中產生的結果，就有機太陽能電池的角度檢視其連續性、分子分布、結構型態等要素，探討在分子比例各不同的條件下形成結構的差異，並研究藉由基板應力產生的異化沉積結構操作薄膜型態的可能性。本論文開發的模擬方法也可以延伸到有機發光二極體的發光層材料的微觀結構研究，從而能夠協助有機光電領域的實驗團隊開發出新一代更為高效的有機太陽能電池或有機發光元件。

In this thesis, we constructed a ellipsoid-based coarse-grained model to study the mesoscale morphology evolution of DPDCPB:C70 small molecule organic solar cells during vacuum co-deposition processes. We coarsed the DPDCPB small molecule donor molecules, and the C70 acceptor molecules into three bonded ellipsoids and one single ellipsoid, respectively. The interactions between ellipsoids are described by the anisotropic Gay-Berne force field. By employing the covariant matrix evolutionary strategy (CMAES), we successfully parameterized the Gay-Berne potential by reproducing the potential energy surfaces from respective all atom atomistic simulations. With the parameterized Gay-Berne potential, for the first time, we are able to carry out molecular simulations of the vacuum co-deposition processes with system size compatible with experiments owing to the significantly reduced system degrees of freedom from coarse-graining. We studied the effects of DPDCPB:C70 deposition ratios, as well as the DPDCPB capping layer residual strains (densities) on the resultant composite film growth modes. Our simulation results indicate that C70 can easily aggregate into clusters regardless of concentrations (C70 deposition ratios). As a result, C70 clusters form the backbone of the film and the growth mode of C70 clusters literally determines the DPDCPB:C70 film morphologies. The residual strain induced by C70 supporting layer beneath the capping layer promote the three-dimensional growth mode of C70, leading to DPDCPB:C70 films with high surface roughness. In contrast, by relaxing the stress in the lateral dimensions, the three-dimensional growth modes can be noticeably suppressed. Hence, we also demonstrates the possibilities of manipulating film morphologies by applying lateral strains in the substrates. This thesis not only provides insights into morphology evolution during vacuum co-deposition processes of small molecule organic solar cells but also pave the pathway toward investigating the mesoscale structures of organic electronic devices such as the organic light emitting diodes (OLEDs).