A tandem organic solar cell (OSC) is a valid structure to widen the photon response range and suppress the transmission loss and thermalization loss. In the past few years, the development of low‐bandgap materials with broad absorption in long‐wavelength region for back subcells has attracted considerable attention. However, wide‐bandgap materials for front cells that have both high short‐circuit current density (JSC) and open‐circuit voltage (VOC) are scarce. In this work, a new fluorine‐substituted wide‐bandgap small molecule nonfullerene acceptor TfIF‐4FIC is reported, which has an optical bandgap of 1.61 eV. When PBDB‐T‐2F is selected as the donor, the device offers an extremely high VOC of 0.98 V, a high JSC of 17.6 mA cm−2, and a power conversion efficiency of 13.1%. This is the best performing acceptor with such a wide bandgap. More importantly, the energy loss in this combination is 0.63 eV. These properties ensure that PBDB‐T‐2F:TfIF‐4FIC is an ideal candidate for the fabrication of tandem OSCs. When PBDB‐T‐2F:TfIF‐4FIC and PTB7‐Th:PCDTBT:IEICO‐4F are used as the front cell and the back cell to construct tandem solar cells, a PCE of 15% is obtained, which is one of best results reported to date in the field of organic solar cells.
The maximum photocurrent in tandem organic solar cells (TOSCs) is often obtained by increasing the thicknesses of sub-cells, which leads to recombination enhancement of such devices and compromises their power conversion efficiency (PCE). In this work, an efficient interconnecting layer (ICL) is developed, with the structure ZnO NPs:PEI/PEI/PEDOT:PSS, which enables TOSCs with very good reproducibility. Then, it is discovered that the optimal thickness of the front sub-cell in such TOSCs can be reduced by increasing the proportion of a non-fullerene acceptor in the active layer. The non-fullerene acceptor used in this work has a much larger absorption coefficient than the donor in the front sub-cell, and the absorption reduction of donor can be well complemented by that of the acceptor when increasing the acceptor proportion, thus leading to a significant overall absorption enhancement even with a thinner film. As a result, the optimal thickness of the front sub-cell is reduced and its charge recombination is suppressed. Ultimately, the use of this ICL combined with fine-turning of the composition in the front sub-cell enables an efficient TOSC with a very high fill factor of 78% and an excellent PCE of 18.71% (certified by an accredited institute to be 18.09%) to be obtained.
Polythiophenes
(PTs) are promising donor materials for the industrialization of polymer
solar cells (PSCs) due to the merits of easy synthesis, low cost,
and large-scale producibility. The rapid progress of non-fullerene
acceptors requires the development of new PTs for use in non-fullerene
PSCs. In this work, we present a set of PTs with different degrees
of backbone fluorination (P6T-F00, P6T-F50, P6T-F75, and P6T-F100)
to investigate the effect of fluorination on the photovoltaic properties
of PTs in non-fullerene PSCs. Upon increasing fluorine content, the
PTs tend to have higher crystallinity, higher absorption coefficients,
and enhanced relative dielectric constants. When blended with a non-fullerene
acceptor EH-IDTBR, the blend films show increased photoluminescence
quenching efficiency, reduced charge recombination loss, and extended
charge carrier lifetime along with increasing fluorine content of
PTs. These positive factors collectively result in dramatically improved
power conversion efficiency from 4.3% for P6T-F00:EH-IDTBR to 7.3%
for P6T-F100:EH-IDTBR, which is superior to the champion binary non-fullerene
PSCs based on P3HT. Our results demonstrate that PTs are promising
donor materials for non-fullerene PSCs via backbone fluorination.
As the power conversion
efficiency (PCE) of polymer solar cells
(PSCs) keeps increasing, developing high-performance large-area PSCs
toward commercial application becomes a hot topic in this field. Here,
we design and synthesize a non-fullerene acceptor TfIF-4Cl with a
fused nonacyclic core via end-group chlorination. Compared to the
fluorinated counterpart (TfIF-4F), the combination of the Cl atom
in TfIF-4Cl not only leads to red-shifted absorption, but also improves
the molecular packing ability. When TfIF-4Cl is blended with the polymer
donor PM7 to fabricate the PSC, the device maintains high V
OC (0.97 V, corresponding to a low energy loss
of 0.60 eV) and presents enhanced J
SC and
high fill factor (78%), thus leading to an improved efficiency of
14% when compared with a PM7:TfIF-4F-based device. The high V
OC but moderate photocurrent of PM7:TfIF-4Cl-based
small-area device are beneficial to achieve large-area devices with
high scalability according to the Joule’s law; thus, we manufacture
1.01 cm2 devices and achieve a remarkable PCE of 13.3%,
which retain 95% in efficiency when the device area is scaled up from
0.04 to 1.01 cm2, and represent the best scalability when
the device area is scaled up to 1 cm2 in the literature.
scite is a Brooklyn-based organization that helps researchers better discover and understand research articles through Smart Citations–citations that display the context of the citation and describe whether the article provides supporting or contrasting evidence. scite is used by students and researchers from around the world and is funded in part by the National Science Foundation and the National Institute on Drug Abuse of the National Institutes of Health.