Nanomorphology of Bulk Heterojunction Photovoltaic Thin Films Probed with Resonant Soft X-ray Scattering

• DOI: 10.1021/nl1009266
• Publication Date: 2010-06-30T16:37:46Z
• Authors: Sufal Swaraj; Cheng Wang; Hongping Yan; Benjamin Watts; Jan Lüning; Christopher R. Mc...; Harald Ade
• Keywords: 02 engineering and technology; 0210 nano-technology; 7. Clean energy

The bulk nanomorphology of organic heterojunction devices, particularly all-polymer is difficult to characterize due limited electron density contrast between constituent materials. Resonant soft X-ray scattering can overcome this problem and used show that the morphologies in chloroform cast subsequently annealed polyfluorene copolymer poly(9,9'-dioctylfluorene-co-bis(N,N'-(4,butylphenyl))bis(N,N'-phenyl-1,4-phenylene)diamine) (PFB) poly(9,9'-dioctylfluorene-co-benzothiadiazole) (F8BT) blends exhibit a hierarchy length scales with impure domains as-cast films. With annealing, these first become purer at smallest scale only then evolve size annealing. Even optimized cells using present fabrication methods are found have dominant domain much larger than exciton diffusion length. observed morphology far from ideal for efficient solar cell operation very different those achieved high-efficiency fullerene-based devices. This strongly implies lack morphological control contributes relatively poor performance PFB/F8BT devices may be problematic general. Novel processing strategies will employed harness full potential high open circuit voltage offer.