Browsing by Author "Meng, Dong"

Now showing 1 - 4 of 4

Enabling High-Performance Tandem Organic Photovoltaic Cells by Balancing the Front and Rear Subcells
(1970-01-01)
Cheng, Pei
;
Wang, Hao-Cheng
;
Zheng, Ran
;
Zhu, Yuan
;
Dai, Shuixing
In tandem organic photovoltaics, the front subcell is based on large-bandgap materials, whereas the case of the rear subcell is more complicated. The rear subcell is generally composed of a narrow-bandgap acceptor for infrared absorption but a large-bandgap donor to realize a high open-circuit voltage. Unfortunately, most of the ultraviolet-visible part of the photons are absorbed by the front subcell; as a result, in the rear subcell, the number of excitons generated on large-bandgap donors will be reduced significantly. This reduces the (photo) conductivity and finally limits the hole-transporting property of the rear subcell. In this work, a simple and effective way is proposed to resolve this critical issue. To ensure sufficient photogenerated holes in the rear subcell, a small amount of an infrared-absorbing polymer donor as a third component is introduced, which provides a second hole-generation and transporting mechanism to minimize the aforementioned detrimental effects. Finally, the short-circuit current density of the two-terminal tandem organic photovoltaic is significantly enhanced from 10.3 to 11.7 mA cm(-2)(while retaining the open-circuit voltage and fill factor) to result in an enhanced power conversion efficiency of 15.1%.
Enhancing photovoltaic performance by tuning the domain sizes of a small-molecule acceptor by side-chain-engineered polymer donors
(2019-02-21)
Lin, Yu-Che
;
Lu, Yi-Ju
;
Tsao, Cheng-Si
;
Saeki, Akinori
;
Li, Jia-Xing
This paper reports two new fluorine-substituted polymer donors (BO2FC8, BO2FEH), with different side-chain architectures, and a new chlorine-substituted small-molecule acceptor (m-ITIC-OR-4Cl) that are capable of simultaneous charge and energy transfer as the binary blend active layer for organic photovoltaics. We first resolved the single-crystal structure of m-ITIC-OR-4Cl and then used simultaneous grazing-incidence wide-and small-angle X-ray scattering to decipher the multi-length-scale structures-such as the shape and size of aggregated domains and molecular orientation-of the blends of BO2FEH and BO2FC8 with m-ITIC-OR-4Cl. The linear side chains of BO2FC8 facilitated its packing and, thus, induced m-ITIC-OR-4Cl to form smaller disc-shaped aggregated domains (thickness: 2.9 nm) than its aggregate domain (thickness: 5.4 nm) in the blend of the branched BO2FEH. That is, the binary blend system of linear-side-chain BO2FC8 with m-ITIC-OR-4Cl featured larger interfacial areas and more pathways for charge transfer and transport, as evidenced by their carrier mobilities. The highest power conversion efficiency (PCE) of 11.0% was that for the BO2FC8: m-ITIC-OR-4Cl device, being consistent with the predicted PCE of 11.2% using machine learning based on random forest algorism; in comparison, the PCE of the BO2FEH:m-ITIC-OR-4Cl device was 6.4%. This study has not only provided insight into the photovoltaic performances of new polymer donor/small-molecule acceptor blends but has also, for the first time, deciphered the hierarchical morphologies-from molecule orientation to nano-domain shape and size-of such blend systems, linking the morphologies to the photovoltaic performances. The use of side-chain architectures suggests an approach for tuning the morphology of the polymer/small-molecule binary blend active layer for use in organic photovoltaics.
Rational Tuning of Molecular Interaction and Energy Level Alignment Enables High-Performance Organic Photovoltaics
(1970-01-01)
Wang, Rui
;
Yuan, Jun
;
Han, Guangchao
;
Huang, Tianyi
;
Huang, Wenchao
The performance of organic photovoltaics (OPVs) has rapidly improved over the past years. Recent work in material design has primarily focused on developing near-infrared nonfullerene acceptors with broadening absorption that pair with commercialized donor polymers; in the meanwhile, the influence of the morphology of the blend film and the energy level alignment on the efficiency of charge separation needs to be synthetically considered. Herein, the selection rule of the donor/acceptor blend is demonstrated by rationally considering the molecular interaction and energy level alignment, and highly efficient OPV devices using both-fluorinated or both-nonfluorinated donor/acceptor blends are realized. With the enlarged absorption, ideal morphology, and efficient charge transfer, the devices based on the PBDB-T-F/Y1-4F blend and PBDB-T-F/Y6 exhibit champion power conversion efficiencies as high as 14.8% and 15.9%, respectively.
Transparent Hole-Transporting Frameworks: A Unique Strategy to Design High-Performance Semitransparent Organic Photovoltaics
(1970-01-01)
Cheng, Pei
;
Wang, Hao-Cheng
;
Zhu, Yuan
;
Zheng, Ran
;
Li, Tengfei
Thanks to the nature of molecular orbitals, the absorption spectra of organic semiconductors are not continuous like those in traditional inorganic semiconductors, which offers a unique application of organic photovoltaics (OPVs): semitransparent OPVs. Recently, the exciting progress of materials design has promoted the development of semitransparent OPVs. However, in the perspective of device engineering, almost all reported works reduce the thickness of back/reflected electrode to obtain high average visible transmittance (AVT), which is a trade-off between power conversion efficiency (PCE) and the transmittance of the whole solar spectrum (visible and infrared), and therefore limit the further development. Herein, a unique strategy of "transparent hole-transporting frameworks" is proposed. A hole-transporting large-bandgap polymer (poly[bis(4-phenyl)(2,4,6-trimethylphenyl)amine (PTAA)) is employed to partially replace polymer donors in the active layer of PBDB-T/Y1. PTAA is a p-type polymer with a large bandgap of 2.9 eV; the partial substitution of PBDB-T by PTAA reduces the absorption of the active layer only in the visible region, keeping the hole-transporting pathways as well as the optimized film morphology. As a result, semitransparent OPVs with PCEs of 12% and AVTs of 20% are achieved, both on rigid and flexible substrates. To demonstrate the generality, this strategy is also used in three different active layers.