Effects of a Fluorinated Donor Polymer on the Morphology, Photophysics, and Performance of All-Polymer Solar Cells Based on Naphthalene Diimide-Arylene Copolymer Acceptors

Duyen K Tran; Nagesh B Kolhe; Ye-Jin Hwang; Daiki Kuzuhara; Tomoyuki Koganezawa; Samson A Jenekhe

doi:10.1021/acsami.0c01382

Effects of a Fluorinated Donor Polymer on the Morphology, Photophysics, and Performance of All-Polymer Solar Cells Based on Naphthalene Diimide-Arylene Copolymer Acceptors

ACS Appl Mater Interfaces. 2020 Apr 8;12(14):16490-16502. doi: 10.1021/acsami.0c01382. Epub 2020 Mar 27.

Authors

Duyen K Tran¹, Nagesh B Kolhe¹, Ye-Jin Hwang², Daiki Kuzuhara³, Tomoyuki Koganezawa⁴, Samson A Jenekhe¹

Affiliations

¹ Department of Chemical Engineering and Department of Chemistry, University of Washington, Seattle, Washington 98195-1750, United States.
² Department of Chemistry and Chemical Engineering, Inha University, 100 Inha-ro, Michuhol-gu, Incheon 22212, Republic of Korea.
³ Faculty of Science and Engineering, Iwate University, 4-3-5 Ueda, Morioka, Morioka, Iwata 020-8551, Japan.
⁴ Industry Application Division, Japan Synchrotron Radiation Research Institute, Sayo, Hyogo 679-5198, Japan.

PMID: 32180406
DOI: 10.1021/acsami.0c01382

Abstract

Naphthalene diimide (NDI)-biselenophene copolymer (PNDIBS), NDI-selenophene copolymer (PNDIS), and the fluorinated donor polymer PM6 were used to investigate how a fluorinated polymer component affects the morphology and performance of all-polymer solar cells (all-PSCs). Although the PM6:PNDIBS blend system exhibits a high open-circuit voltage (V_oc = 0.925 V) and a desired low optical bandgap energy loss (E_loss = 0.475 eV), the overall power conversion efficiency (PCE) was 3.1%. In contrast, PM6:PNDIS blends combine a high V_oc (0.967 V) with a high fill factor (FF = 0.70) to produce efficient all-PSCs with 9.1% PCE. Furthermore, the high-performance PM6:PNDIS all-PSCs could be fabricated by various solution processing approaches and at active layer thickness as high as 300 nm without compromising photovoltaic efficiency. The divergent photovoltaic properties of PNDIS and PNDIBS when paired respectively with PM6 are shown to originate from the starkly different blend morphologies and blend photophysics. Efficient PM6:PNDIS blend films were found to exhibit a vertical phase stratification along with lateral phase separation, while the molecular packing had a predominant face-on orientation. Bulk lateral phase separation with both face-on and edge-on molecular orientations featured in the poor-performing PM6:PNDIBS blend films. Enhanced charge photogeneration and suppressed geminate and bimolecular recombinations with 99% charge collection probability found in PM6:PNDIS blends strongly differ from the poor charge collection probability (66%) and high electron-hole pair recombination seen in PM6:PNDIBS. Our findings demonstrate that beyond the generally expected enhancement of V_oc, a fluorinated polymer component in all-PSCs can also exert a positive or negative influence on photovoltaic performance via the blend morphology and blend photophysics.

Keywords: all-polymer solar cells; blend morphology; fluorinated donor polymer; naphthalene diimide−arylene copolymer; thick-film active layer; vertical phase stratification.