Simutaneously high open circuit voltage and high short circuit current density is a big challenge for achieving high efficiency polymer solar cells due to the excitonic nature of organic semdonductors. Herein, we developed a trialkylsilyl substituted 2D-conjugated polymer with the highest occupied molecular orbital level down-shifted by Si–C bond interaction. The polymer solar cells obtained by pairing this polymer with a non-fullerene acceptor demonstrated a high power conversion efficiency of 11.41% with both high open circuit voltage of 0.94 V and high short circuit current density of 17.32 mA cm−2 benefitted from the complementary absorption of the donor and acceptor, and the high hole transfer efficiency from acceptor to donor although the highest occupied molecular orbital level difference between the donor and acceptor is only 0.11 eV. The results indicate that the alkylsilyl substitution is an effective way in designing high performance conjugated polymer photovoltaic materials.
Low bandgap n-type organic semiconductor (n-OS) ITIC has attracted great attention for the application as an acceptor with medium bandgap p-type conjugated polymer as donor in nonfullerene polymer solar cells (PSCs) because of its attractive photovoltaic performance. Here we report a modification on the molecular structure of ITIC by side-chain isomerization with meta-alkyl-phenyl substitution, m-ITIC, to further improve its photovoltaic performance. In a comparison with its isomeric counterpart ITIC with para-alkyl-phenyl substitution, m-ITIC shows a higher film absorption coefficient, a larger crystalline coherence, and higher electron mobility. These inherent advantages of m-ITIC resulted in a higher power conversion efficiency (PCE) of 11.77% for the nonfullerene PSCs with m-ITIC as acceptor and a medium bandgap polymer J61 as donor, which is significantly improved over that (10.57%) of the corresponding devices with ITIC as acceptor. To the best of our knowledge, the PCE of 11.77% is one of the highest values reported in the literature to date for nonfullerene PSCs. More importantly, the m-ITIC-based device shows less thickness-dependent photovoltaic behavior than ITIC-based devices in the active-layer thickness range of 80-360 nm, which is beneficial for large area device fabrication. These results indicate that m-ITIC is a promising low bandgap n-OS for the application as an acceptor in PSCs, and the side-chain isomerization could be an easy and convenient way to further improve the photovoltaic performance of the donor and acceptor materials for high efficiency PSCs.
All-polymer solar cells (all-PSCs) offer unique morphology stability for the application as flexible devices, but the lack of high-performance polymer acceptors limits their power conversion efficiency (PCE) to a value lower than those of the PSCs based on fullerene derivative or organic small molecule acceptors. We herein demonstrate a strategy to synthesize a high-performance polymer acceptor PZ1 by embedding an acceptor-donor-acceptor building block into the polymer main chain. PZ1 possesses broad absorption with a low band gap of 1.55 eV and high absorption coefficient (1.3×10 cm ). The all-PSCs with the wide-band-gap polymer PBDB-T as donor and PZ1 as acceptor showed a record-high PCE of 9.19 % for the all-PSCs. The success of our polymerization strategy can provide a new way to develop efficient polymer acceptors for all-PSCs.
Achieving efficient charge transfer
at small frontier molecular
orbital offsets between donor and acceptor is crucial for high performance
polymer solar cells (PSCs). Here we synthesize a new wide band gap
polymer donor, PTQ11, and a new low band gap acceptor, TPT10, and
report a high power conversion efficiency (PCE) PSC (PCE = 16.32%)
based on PTQ11–TPT10 with zero HOMO (the highest occupied molecular
orbital) offset (ΔE
HOMO(D–A)). TPT10 is a derivative of Y6 with monobromine instead of bifluorine
substitution, and possesses upshifted lowest unoccupied molecular
orbital energy level (E
LUMO) of −3.99
eV and E
HOMO of −5.52 eV than Y6.
PTQ11 is a derivative of low cost polymer donor PTQ10 with methyl
substituent on its quinoxaline unit and shows upshifted E
HOMO of −5.52 eV, stronger molecular crystallization,
and better hole transport capability in comparison with PTQ10. The
PSC based on PTQ11–TPT10 shows highly efficient exciton dissociation
and hole transfer, so that it demonstrates a high PCE of 16.32% with
a higher V
oc of 0.88 V, a large J
sc of 24.79 mA cm–2, and a
high FF of 74.8%, despite the zero ΔE
HOMO(D–A) value between donor PTQ11 and acceptor TPT10. The PCE of 16.32%
is one of the highest efficiencies in the PSCs. The results prove
the feasibility of efficient hole transfer and high efficiency for
the PSCs with zero ΔE
HOMO(D–A), which is highly valuable for understanding the charge transfer
process and achieving high PCE of PSCs.
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