Hydrogen bond induced high performance ternary fullerene-free organic solar cells with increased current density and enhanced stability

et al. 2021

Adv Funct Materials

Self Cite

Exciplex emitters have been extensively studied owing to their natural thermally activated delayed fluorescence characteristic, and many efforts have been made to improve their performance in organic light emitting diodes (OLEDs). In this work, the authors propose a novel strategy by introducing intermolecular hydrogen bond (HB) between electron‐donating and electron‐accepting constituting molecules (D and A) to suppress non‐radiative transition of exciplex emitters and thus improve their efficiencies and stabilities in the OLEDs. Accordingly, three exciplex emitters are constructed by using 1,3‐di(10H‐phenoxazin‐10‐yl)benzene (13PXZB) as donor and 4,6‐bis(3,5‐di(pyridin‐4‐yl)phenyl)‐2‐methylpyrimidine (B4PyMPM), 4,6‐bis(3,5‐di(pyridin‐3‐yl)phenyl)‐2‐methylpyrimidine (B3PyMPM), and 4,6‐bis(3,5‐di(pyridin‐2‐yl)phenyl)‐2‐methylpyrimidine (B2PyMPM) as acceptors. With the most intermolecular HBs, 13PXZB:B4PyMPM shows the highest photoluminescence quantum yield (69.6%) and the lowest rate constant of non‐radiative process of triplet excitons (3.4 × 105 S−1). And the OLED using 13PXZB:B4PyMPM as the emitter successfully exhibits a much higher external quantum efficiency of 14.6% than other contrastive devices. Moreover, the half lifetime of 13PXZB:B4PyMPM is 4.8 and 8.2 times higher than those of 13PXZB:B3PyMPM and 13PXZB:B2PyMPM in the devices. This work not only demonstrates that intermolecular HBs between D and A molecules can improve the performance of exciplex emitters, but also paves a new route to develop efficient and stable exciplex emitters.

Section: Resultsmentioning

confidence: 99%

“…The enhancements of the shorter‐wavelength peaks suggest the formations of intermolecular HBs between 13PXZB and B4PyMPM and 13PXZB and B3PyMPM. [ 33,34 ]…”

Section: Resultsmentioning

confidence: 99%

Hydrogen‐Bond‐Assisted Exciplex Emitters Realizing Improved Efficiencies and Stabilities in Organic Light Emitting Diodes

Zhang

Zheng

et al. 2021

Adv Funct Materials

Self Cite

“…In order to verify our hypothesis about formation of such H‐bonds, we carried out the FTIR spectroscopy on the ITIC, IT‐OH, and IT‐DOH films with different thicknesses. As shown in Figure 4 , a characteristic vibrational peak of CN groups at 2219 cm −1 is observed for all samples, while the stretching signals of CO groups in the three molecules obviously differ, locating between 1650 and 1720 cm −1 . The CO peak for ITIC and IT‐DOH is seen at 1703 and 1680 cm −1 , respectively.…”

Section: Figurementioning

confidence: 80%

H‐Bonds‐Assisted Molecular Order Manipulation of Nonfullerene Acceptors for Efficient Nonannealed Organic Solar Cells

Advanced Energy Materials

Xiao

et al. 2020

Various substituents have been incorporated into nonfullerene acceptors (NFAs) to modulate absorption scopes and energy levels for boosting efficiencies of organic solar cells (OSCs). The manipulation of the NFAs' molecular order and crystallinity via those substitutions is equally crucial to OSC performances, which yet remains interesting and challenging. The hydroxyl group, which can potentially form strong intermolecular hydrogen bonds (H‐bonds) for improving molecular arrangements, has, however, never been considered. Herein, two hydroxyl‐functionalized NFAs, IT‐OH with one hydroxyl and IT‐DOH with two hydroxyls, are synthesized to tune the molecular packing and crystallinity. The ordered molecular arrangement and higher crystallinity are observed for the IT‐OH and IT‐DOH than the parent ITIC. This is assigned to the formation of intermolecular H‐bonds induced by the hydroxyls, which elongates molecular conjugated planes leading to long‐range‐ordered structures via π–π stacking. By the appropriate crystallinity and miscibility with donor polymer, an IT‐DOH‐based nonannealed OSC affords an efficiency of 12.5% with good device stability. This work provides a promising strategy to tune the molecular packing and crystallinity to design NFAs by introducing hydroxyl groups.

“…Two difficulties must be overcome simultaneously to balance the trade-off between the efficiency and stability. One difficulty is to maintain a stable morphology of novel donor/acceptor (D/A) blends in highly efficient OPVs, which can easily change even at RT (23,28,29). Another difficulty is to fabricate an HTL with stable interfaces among other layers, so that the interfacial morphology and/or properties can be modulated by a high-temperature aging process (18,19).…”

Section: Significancementioning

confidence: 99%

Highly efficient organic photovoltaics with enhanced stability through the formation of doping-induced stable interfaces

Jiang

Proc. Natl. Acad. Sci. U.S.A.

Fukuda

et al. 2020

Flexible organic photovoltaics (OPVs) are promising power sources for wearable electronics. However, it is challenging to simultaneously achieve high efficiency as well as good stability under various stresses. Herein, we demonstrate the fabrication of highly efficient (efficiency, 13.2%) and stable OPVs based on nonfullerene blends by a single-step postannealing treatment. The device performance decreases dramatically after annealing at 90 °C and is fully recovered after annealing at 150 °C. Glass-encapsulated annealed OPVs show good environmental stability with 4.8% loss in efficiency after 4,736 h and an estimatedT80lifetime (80% of the initial power conversion efficiency) of over 20,750 h in the dark under ambient condition andT80lifetime of 1,050 h at 85 °C and 30% relative humidity. This environmental stability is enabled by the synergetic effect of the stable morphology of donor/acceptor blends and thermally stabilized interfaces due to doping. Furthermore, the high efficiency and good stability are almost 100% retained in ultraflexible OPVs and minimodules which are mechanically robust and have long-term operation capability and thus are promising for future self-powered and wearable electronics.