nanoGe - HOPV15 - From Molecular Packing to Charge Collection - Modelling Fundamental Processes in SiIDT-BT:PCBM Derivative Blends.

From Molecular Packing to Charge Collection - Modelling Fundamental Processes in SiIDT-BT:PCBM Derivative Blends.

James R. Durrant^a, Jenny Nelson^a, Stoichko D. Dimitrov^a, Dorota Niedzialek^a, Bob C. Schroeder^b, Joseph R. Kline^c

^aImperial College London, United Kingdom, South Kensington, Londres, Reino Unido, United Kingdom

^bStanford University, Stanford, CA 94305, United States

^cNIST, 100 Bureau Drive, Stop 8300, Gaithersburg, MD 20899-8300, United States

International Conference on Hybrid and Organic Photovoltaics
Proceedings of International Conference on Hybrid and Organic Photovoltaics 2015 (HOPV15)

Roma, Italy, 2015 May 11th - 13th

Organizer: Filippo De Angelis

Oral, Dorota Niedzialek, presentation 404
Publication date: 5th February 2015

Identifying and understanding the key structure-property relationships that govern the electronic properties of organic materials is of utmost importance for boosting the efficiencies of devices. For example, in organic solar cells the photocurrent generation efficiency depends critically on charge separation processes which depend, in turn, on both (i) the chemical structure and (ii) the microstructural organization of the material. Several experimental and theoretical studies reveal that charge separation efficiency is influenced by electronic energy level alignment at interfaces, degree of delocalisation of the excited states - and hence crystallinity - and competition with loss processes such as recombination to triplets. Charge separation and in turn, device performance are therefore decided by the interplay between these factors. In this work we aim to understand the relative importance of these factors in blend systems with silicon bridged indacenodithiophene copolymer (Si-IDT-BT) derivatives as the donor and PCBM as the acceptor material. These materials have shown interesting differences in photoinduced polaron generation efficiency, relative to triplet formation, as a result of small changes in chemical structure. These differences correlate to differences in both the energy level alignment of the donor:acceptor pair and in the crystallinity of the polymers. We investigate the energy and nature of excited electronic states (singlet (S1), triplet (T1) and charge transfer (CT) states) by performing a series of Density Functional Theory calculations. We report a systematic theoretical study at the Molecular Mechanics level of the molecular packing of the Si-IDT-BT copolymers. Additionally, we estimate the role that chemical structure modifications of different Si-IDT-BT copolymer derivatives and their supramolecular organisation have on intra- and interchain charge transport properties. We attempt to explain the differences in charge generation efficiency and photocurrent generation in devices in terms of these results.

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