With rapid development for tens of years, organic solar cells (OSCs) have attracted much attention for their potential in practical applications. As an important photovoltaic parameter, the fill factor (FF) of OSCs stands for the effectiveness of charge generation and collection, which significantly depends on the properties of the interlayer and active layer. Here, a facile and effective strategy to improve the FF through hole-transporting layer (HTL) modification is demonstrated. By mixing WO nanoparticles with a poly(3,4-ethylenedioxythiophene):polystyrene sulfonate (PEDOT:PSS) emulsion, the surface free energy of the HTL is improved and the morphology of the active layer is optimized. Benefiting from increased carrier lifetime, a device based on WO :PEDOT:PSS HTL exhibits a boosted performance with an FF of 80.79% and power conversion efficiency of 14.57% PCE. The results are certified by the National Institute of Metrology (NIM), which, to date, are the highest values in this field with certification. This work offers a simple and viable option of HTL modification to realize highly efficient OSCs.
The solution-processed layer-by-layer (LBL) method has potential to achieve high-performance polymer solar cells (PSCs) due to its advantage of enriching donors near the anode and acceptors near the cathode. However, power conversion efficiencies (PCEs) of the LBL-PSCs are still significantly lower than those of conventional one-step-processed PSCs (OS-PSCs). A method to solve the critical problems in LBL-PSCs is reported here. By employing a specific mixed solvent (o-dichlorobenzene [o-DCB]/tetrahydrofuran) to spin-coat the small-molecular acceptor IT-4F onto a layer of the newly designed polymer donor (PBDB-TFS1), appropriate interdiffusion between the PBDB-TFS1 and the IT-4F can critically be controlled, and then an ideal phase separation of the active layer and large donor/acceptor interface area can be realized with a certain amount of o-DCB. The PSCs based on the LBL method exhibit PCEs as high as 13.0%, higher than that of the counterpart (11.8%) made by the conventional OS solution method. This preliminary work reveals that the LBL method is a promising approach to the promotion of the photovoltaic performance of polymer solar cells.
Conspectus
Rylene imides are oligo(peri-naphthalene)s bearing
one or two six-membered carboxylic imide rings. Their flexible reaction
sites and unique photoelectronic properties have afforded active research
for applications in photovoltaic devices, light-emitting diodes, and
fluorescent sensors. Over the past few decades, synthetic flexibility
along with the evolution of molecular design principles for novel
aromatic imides has rendered these intriguing dyes considerably valuable,
especially for organic photovoltaics (OPVs).
During the course
of molecular evolution, the most difficult criterion
to meet is how to modulate the intra- and intermolecular interactions
to alter the aggregation behavior of rylene imides as well as their
compatibility with donor materials, with the prerequisite that the
appropriate molecular energy level is maintained. In the meantime,
our group has focused on the precise synthesis of π-extended
rylene imide electron acceptors (RIAs) to rationally alter the molecular
chemical and electronic structure, packing arrangement, and photoelectronic
properties. These powerful molecular design strategies include the
construction of a fully conjugated rigid multichromophoric architecture
and successful integration of heteroatoms. Herein, these multichromophoric
oligomers are precisely defined as giant rylene imides. Importantly,
these strategies provide a vast space for progress in RIAs and present
a more comprehensive structure–performance relationship network
that can be distinguished from other electron acceptor systems. In
particular, the successful acquisition of these fused superhelical
architectures provides a meaningful reference for the pluralistic
development of OPVs, such as triplet organic solar cells and polarized-light
photovoltaic detectors. Meanwhile, the introduction of heteroatoms
into the rylene conjugated skeleton provides donor/acceptor interfaces
with enhanced electronic interactions and thereby suppresses the polaron-pair
binding energy. Nonetheless, much remains to be implemented to broaden
the absorption capability of rylene imides as well as to realize full
utilization of these meaningful chiral isomers with a wide and strong
UV–vis spectroscopic response.
In this Account, we provide
an overview of our novel approaches
toward a supermolecular framework and of the reformed molecular design
principle for rylene imide-based electron acceptors since 2012. We
begin with a discussion of the rapidly emerging synthesis strategies
for giant rylene imides. Then several typical examples with remarkable
photovoltaic properties and unique working mechanisms are selected,
aimed at providing an in-depth discussion of structure–property–performance
relationships. The remaining challenges and newly emerging research
information for giant rylene imide-based electron acceptors are further
put forward. It is our aspiration that this Account will trigger intensive
research interest in these pluralist rylene-based electron acceptors,
thereby further accelerating the profound sustainable dev...
The straightforward palladium-catalyzed synthesis protocol toward spiro-fused perylene diimides is developed. The reaction involves two palladium-catalyzed C-H activations and 4-fold C-C bond formation sequence from readily available precursors. This facile and step-economic approach also provides another convenient access to ethylene-bridged dimer (NDP) and further π-extended spiro system (SNTP). In addition, the molecular structure of spirodiperylenetetraimide (SDP) is illustrated to show a three-dimensional (3D) cruciform configuration, and its absorbance is distinctly red-shifted due to the significant spiroconjugation effect. With combined properties of broadened and intensive absorption, aligned LUMO levels, and unique molecular geometry, the spiro-fused PDI system represents a new kind of high-performance semiconducting framework as the electron acceptor in high-efficiency organic solar cells.
This review describes developments of non-fullerene small molecular acceptors in solar cells since 2015, including rylene imide, indacenodithiophene and diketopyrrolopyrrole.
This work discussed the effect of energy-level offset on photovoltaic performance of PBDB-TF-based non-fullerene OSCs and established a correlation between them.
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