A ternary strategy has been considered to be a simple
and efficient
method to further improve the performance of organic solar cells (OSCs).
Here, three benzotriazole-based nonfullerene acceptors (NFAs) with
similar A2-A1-D-A1-A2 backbones
except for different terminal groups, are utilized as guest components
to a classic PM6:BTP-BO-4F binary host. Excitingly, BTA1–3
all realize much better photovoltaic performance in ternary devices
with a minimized energy loss (E
loss) and
improved open-circuit voltage (V
OC), suggesting
that it is the bridge A1 unit that plays the decisive role.
Additionally, the short-circuit current density (J
SC) and fill factor (FF) of BTA2-/BTA3-incorporated devices
can be enhanced simultaneously, resulting from more efficient photon
harvesting, increased exciton dissociation, improved charge transport,
and reduced charge recombination. The highest efficiency of 18.27%
is obtained in the BTA2 device, one of the top values for PM6-based
OSCs. This work suggests that A2-A1-D-A1-A2 type NFAs are effective in further improving
the performance of ternary OSCs.
The innovation of photovoltaic materials, [1][2][3][4][5] specially nonfullerene acceptors (NFAs), has pioneered many research hot spots of organic solar cells (OSCs) for in-depth exploration in the past decades. With combinational efforts devoted to molecule evolution and device engineering, the power conversion efficiency (PCE) of single-junction solar cells has approached up to 19%. [6][7][8] Various NFAs have been developed in recent years, such as diketopyrrolopyrrole (DPP) or perylene diimide (PDI) contained molecules, [9][10][11] A-D-A-type acceptors, i.e., ITIC, [12,13] M series [14] and Y series molecules, [15][16][17][18] typically Y6. [19] Core engineering has been demonstrated effective to achieve highperformance NFAs, as molecular conjugation and intramolecular charge transfer (ICT) can be readily realized through introducing or removing the aromatic rings on the backbone of NFAs. Additionally, the asymmetric strategy was adopted for molecule modification, which could precisely regulate the intrinsic optoelectronic properties of NFAs. Derived from symmetric NFAs, i.e., ITIC [12] and IT-4F, [20] various A-D-A-type asymmetric NFAs have been designed and synthesized. [21,22] Sun's group designed asymmetric TPTT-2F and TPTTT-2F through extending molecular conjugation of the IDT core. [23] Along with the enhanced conjugation, redshifted
The interfacial contacts between the electron transporting layers (ETLs) and the photoactive layers are crucial to device performance and stability for OSCs with inverted architecture. Herein, atomic layer deposition (ALD) fabricated ultrathin Al2O3 layers are applied to modify the ETLs/active blends (PM6:BTP‐BO‐4F) interfaces of OSCs, thus improving device performance. The ALD‐Al2O3 thin layers on ZnO significantly improved its surface morphology, which led to the decreased work function of ZnO and reduced recombination losses in devices. The simultaneous increase in open‐circuit voltage (), short‐circuit current density () and fill factor (FF) were achieved for the OSCs incorporated with ALD‐Al2O3 interlayers of a certain thickness, which produced a maximum PCE of 16.61%. Moreover, the ALD‐Al2O3 interlayers had significantly enhanced device stability by suppressing degradation of the photoactive layers induced by the photocatalytic activity of ZnO and passivating surface defects of ZnO that may play the role of active sites for the adsorption of oxygen and moisture.
Incorporating ITIC derivatives as guest acceptors into binary host systems is an effective strategy for constructing high-performance ternary organic solar cells (TOSCs). In this work, we introduced A−D−A type ITIC derivatives PTBTT-4F (asymmetric) and PTBTP-4F (symmetric) into the PM6:BTP-BO-4F (Y6-BO) binary blend and investigated the impacts of two guest acceptors on the performance of TOSCs. Differentiated device performance was observed, although PTBTT-4F and PTBTP-4F presented similar chemical structures and comparable absorptions. The PTBTT-4F ternary devices exhibited an improved power conversion efficiency (PCE) of 17.67% with increased open circuit (V OC ) and current density (J SC ), whereas the PTBTP-4F-based ternary devices yielded a relatively lower PCE of 16.34%. PTBTT-4F showed much better compatibility with the host acceptor BTP-BO-4F, so that they formed a well-mixed alloy phase state; more precise phase separation and increased crystallinity were thus induced in the ternary blends, leading to reduced molecular recombination and improved charge mobilities, which contributed to improved fill factors of the ternary devices. In addition, the optimized PTBTT-4F devices exhibited good performance tolerance of the photoactive layer thickness, as they even delivered a PCE of 15.25% when the active layer was as thick as up to ∼300 nm.
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