THESIS
2021
1 online resource (x, 77 pages) : illustrations (some color)
Abstract
Energy losses significantly reduce the open-circuit voltage even among current state-of-the-art organic solar cells (OSCs) which limits the further enhancement of their power conversion
efficiencies (PCEs). In this study, the bulk heterojunction blends of PM6 donor and
halogenated nonfullerene acceptors (NFAs) were found to display a tradeoff behavior
between radiative energy losses, i.e., charge transfer state (CTS) radiative energy loss and the
loss associated with CTS formation from acceptor singlet excitons (SE). In addition, the
efficiency of CTS radiative decay is found to demonstrate competition with the nonradiative
decay which extends even on thermally degraded devices. Accordingly, this work provides
further understandings of energy losses relevant to overcome the current limi...[
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Energy losses significantly reduce the open-circuit voltage even among current state-of-the-art organic solar cells (OSCs) which limits the further enhancement of their power conversion
efficiencies (PCEs). In this study, the bulk heterojunction blends of PM6 donor and
halogenated nonfullerene acceptors (NFAs) were found to display a tradeoff behavior
between radiative energy losses, i.e., charge transfer state (CTS) radiative energy loss and the
loss associated with CTS formation from acceptor singlet excitons (SE). In addition, the
efficiency of CTS radiative decay is found to demonstrate competition with the nonradiative
decay which extends even on thermally degraded devices. Accordingly, this work provides
further understandings of energy losses relevant to overcome the current limitations
concerning OSCs developments. Further, due to the high similarity of molecular fragments
and functionalities between polymer donors and non-fullerene acceptors, the spatial
molecular distributions are commonly not given enough considerations among other studies.
This work demonstrates how vertical phase segregations and microscopic characteristics can
influence the device performance and properties of NFA-based OSCs using time-of-flight
secondary ion mass spectrometry (TOF-SIMS) molecular depth profiling and other optical and
electronic characterizations. This study then also provides enlightenments to enable more
precise and consistent data interpretations among future related studies.
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