THESIS
2022
1 online resource (xix, 143 pages) : illustrations (some color)
Abstract
Organic solar cells (OSCs) have attracted extensive attention of scientists due to their light weight,
low cost, solution processability, flexibility and many other advantages. With the joint efforts of
the research community, the power conversion efficiency (PCE) of single-junction OSCs has
exceeded 19% thanks to the rapid development of non-fullerene acceptors (NFAs), showing great
application prospects. However, NFAs are still facing several problems, such as complex synthetic
route, limited absorption range and unfavorable morphology when blending with donor polymer.
Therefore, more detailed research needs to be conducted to figure out the structure-property
relationships of NFAs. In this thesis, NFAs with non-fused cores and fused cores were designed
and synthesized. The structure-...[
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Organic solar cells (OSCs) have attracted extensive attention of scientists due to their light weight,
low cost, solution processability, flexibility and many other advantages. With the joint efforts of
the research community, the power conversion efficiency (PCE) of single-junction OSCs has
exceeded 19% thanks to the rapid development of non-fullerene acceptors (NFAs), showing great
application prospects. However, NFAs are still facing several problems, such as complex synthetic
route, limited absorption range and unfavorable morphology when blending with donor polymer.
Therefore, more detailed research needs to be conducted to figure out the structure-property
relationships of NFAs. In this thesis, NFAs with non-fused cores and fused cores were designed
and synthesized. The structure-property relationships and their photovoltaic performance were
systematically studied. The ternary strategy of OSCs is also discussed to further enhance the
efficiency of OSCs.
In Chapter II, two unfused-ring acceptors (UFAs) with an A-DA’D-A structure were synthesized.
Generally, UFAs offer simple chemical structures owning simplified synthesis methods and high
overall yield, which would boost commercialization of OSCs in the future. In this work, we
developed the Y6-like A-DA’D-A framework to A-D-A’-D-A-type backbone adopted in building
up UFAs. Two new Y6-like UFAs are synthesized out within 4 steps and are studied the effect of
non-covalent atoms at central electron deficient core on material properties and device
performances. When blended with another economical donor, PTQ10, F substitution at the benzothiadiazole ring is more effective than O substitution, leading to the increased short-circuit
current density (J
SC) and higher efficiencies of over 12%, among the best performances of UFA-based
OSCs. We accomplished a high-performance OSC system using both easily synthesized
donor and acceptor. This contribution demonstrates that the appropriate introduction of non-covalent
interaction is a promising method for modulating energy levels, absorption and
aggregation of A-D-A’-D-A UFAs, thus enhancing their OSC performances.
Chapter III discussed the substitution effect of selenium-incorporated heterocycles on Y6-like SMAs.
In this work, we used the selenium (Se) substitution strategy and developed two new Y6-type SMAs to
study the effect of Se atoms on material properties and device performances. It is found that the
introduction of Se atoms can red-shift the absorption spectra and enhance the aggregation of the
resulting SMAs. Interestingly, the variations in the substitution positions of Se atoms induces different
intramolecular charge transfer within the SMAs. Se substitution at the benzothiadiazole ring is more
effective than those at the thienothiophene rings, leading to the increased J
SC and higher efficiencies of
over 16%. This contribution suggests that appropriate Se substitution is a promising method for
optimizing absorption and aggregation of Y6-type SMAs, thus enhancing their OSC performances.
Chapter IV demonstrates a ternary strategy by using a blue-shifted small molecule donor (SMD) with
both wider bandgap and higher crystallinity to achieve high-performance OSCs. In this work, we
intentionally blue-shift the absorption of a state-of-art SMD (BTR-Cl) by linking the beta position of
the outer thiophene to the alpha position of inner thiophene unit. The resulting molecule β-S1 shows a
maximum absorption peak at 505nm in film state, which exhibits wider bandgap and forms
complementary absorption with the host system (PM6:Y6). The corresponding ternary OSCs with
20%wt β-S1 show significantly enhanced efficiency from 16.2% to 17.1% due to the increased J
SC and
improved fill factor (FF).
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