Ring Substituents Mediate the Morphology of PBDTTPD-PCBM Bulk-Heterojunction Solar Cells

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• 作者：Julien Warnan ; Abdulrahman El Labban ; Cl茅ment Cabanetos ; Eric T. Hoke ; Pradeep Kumar Shukla ; Chad Risko ; Jean-Luc Br茅das ; Michael D. McGehee ; Pierre M. Beaujuge
• 刊名：Chemistry of Materials
• 出版年：2014
• 出版时间：April 8, 2014
• 年：2014
• 卷：26
• 期：7
• 页码：2299-2306
• 全文大小：504K
• 年卷期：v.26,no.7(April 8, 2014)
• ISSN：1520-5002

文摘

Among 蟺-conjugated polymer donors for efficient bulk-heterojunction (BHJ) solar cell applications, poly(benzo[1,2-b:4,5-b鈥瞉dithiophene鈥搕hieno[3,4-c]pyrrole-4,6-dione) (PBDTTPD) polymers yield some of the highest open-circuit voltages (V_OC, ca. 0.9 V) and fill-factors (FF, ca. 70%) in conventional (single-cell) BHJ devices with PCBM acceptors. In PBDTTPD, side chains of varying size and branching affect polymer self-assembly, nanostructural order, and impact material performance. However, the role of the polymer side-chain pattern in the intimate mixing between polymer donors and PCBM acceptors, and on the development of the BHJ morphology is in general less understood. In this contribution, we show that ring substituents such as furan (F), thiophene (T) and selenophene (S)鈥攊ncorporated into the side chains of PBDTTPD polymers鈥攃an induce significant and, of importance, very different morphological effects in BHJs with PCBM. A combination of experimental and theoretical (via density functional theory) characterizations sheds light on how varying the heteroatom of the ring substituents impacts (i) the preferred side-chain configurations and (ii) the ionization, electronic, and optical properties of the PBDTTPD polymers. In parallel, we find that the PBDT(X)TPD analogs (with X = F, T, or S) span a broad range of power conversion efficiencies (PCEs, 3鈥?.5%) in optimized devices with improved thin-film morphologies via the use of 1,8-diiodooctane (DIO), and discuss that persistent morphological impediments at the nanoscale can be at the origin of the spread in PCE across optimized PBDT(X)TPD-based devices. With their high V_OC 1 V, PBDT(X)TPD polymers are promising candidates for use in the high-band gap cell of tandem solar cells.