Scanning Probe Microscopy Analysis of Nonfullerene Organic Solar Cells

• DOI: 10.1021/acsami.0c06048
• Publication Date: 2020-05-29T06:17:55Z
• Authors: Irving Caballero-...; Olivia Amargós-Reyes; José-Luis Maldonado; Juan Nicasio-Collazo; Daniel Romero-Borja; Denisse Barreiro-...; Gábor Molnár; Azzedine Bousseksou
• Keywords: Organic solar cells; Electrical/electronic determinations; Scanning probe microscopies; Nanoscale morphology; [CHIM.COOR]Chemical Sciences/Coordination chemistry; ITIC; 02 engineering and technology; Nanoscale characterization; PBDB-T; 0210 nano-technology; 7. Clean energy

In this work, scanning probe microscopies (SPMs) are used for the analysis of PBDB-T, ITIC, and PBDB-T:ITIC layers of solar cells (OSCs). Scanning tunneling microscopy (STM) images of PBDB-T reveal that thin films (<1 nm) tend to form worm-like pattern (amorphous type) domains with an average chain-to-chain distance of 950 pm; likewise, STM images of ITIC show that side arms form chain-like patterns. STM images of PBDB-T:ITIC blend suggest why PBDB-T domains could facilitate charge dissociation. Further, a strong interchain π-π interaction of the ITIC molecules could promote self-organization, and under the mutual interaction with the PBDB-T polymer, it could influence the pathway formation for electron transport. Moreover, when correlating electrostatic force microscopy (EFM) and photoconductive atomic force microscopy (pc-AFM), the blend morphology and its electrical/electronic properties are determined; the ideal domain size of PBDB-T:ITIC blend phases for maximizing the generated photocurrent is 15-35 nm. Furthermore, phase contrast and surface electric potential characteristics with Kelvin probe force microscopy (KPFM) are measured to examine additional details about the surface and potential changes due to the domain differences in the active layer. OSCs based on the nonfullerene PBDB-T:ITIC active layer reach an average power conversion efficiency (PCE) of 9.1% (best 9.2%).