Zhen Wang

Though organic solar cells (OSCs) have achieved remarkable progress recently, the intrinsic limitation of the “seesaw effect” between open‐circuit voltage ( V _oc ) and short‐circuit current density ( J _sc ) hinders their further improvements. In this study, a fluorescent small molecule, namely SD‐EDOT, is incorporated into the widely used PM6:BTP‐eC9 system to overcome this challenge. The addition of SD‐EDOT lowers the energetic disorder and electron–phonon coupling within the system. More importantly, it forms an energy cascade between donor and acceptor, enabling a side cascade energy transfer pathway and a more favorable energetic landscape. The high fluorescent property of SD‐EDOT improves the utilization rate of high‐energy excitons. These effects collectively promote faster and more efficient charge generation (improving J _sc ), deeper highest occupied molecular orbit of donors, and suppressed non‐radiative energy loss (elevating V _oc ). Consequently, the ternary devices achieve simultaneously higher V _oc and J _sc , significantly boosting the power conversion efficiency from 18.75% to 20.72%. This study provides a rational strategy for mitigating the V _oc – J _sc trade‐off by incorporating a highly fluorescent third component with tailored energy levels, offering a promising pathway toward higher‐performance OSCs.

The relatively high non‐radiative energy loss has become a major limiting factor for improving the performance of organic solar cells (OSCs), with triplet exciton formation being a primary source. Narrowing the energy gap between the first singlet and triplet excited states (Δ E _ST ) in low‐bandgap acceptors is considered an effective strategy to mitigate this issue. In this work, we design and synthesize a dimeric acceptor, DY‐TXT, utilizing a thermally activated delayed fluorescence (TADF) molecule as the bridging unit. This novel structure exhibits a higher photoluminescence quantum yield and a significantly reduced Δ E _ST (∼0.1 eV) compared to conventional nonfullerene acceptors. When incorporated into the D18:L8‐BO host system, DY‐TXT enhances the electroluminescence quantum efficiency and markedly suppresses triplet exciton generation, thereby reducing energy loss via triplet states. The small Δ E _ST also facilitates reverse intersystem crossing process, enabling recycling of triplet excitons. Consequently, the resulting ternary device achieves a low non‐radiative energy loss of 0.194 eV and an outstanding power conversion efficiency of 20.85%. This work demonstrates an effective strategy for suppressing triplet‐mediated energy losses and provides a promising avenue for advancing the performance of OSCs.

The relatively high non‐radiative energy loss has become a major limiting factor for improving the performance of organic solar cells (OSCs), with triplet exciton formation being a primary source. Narrowing the energy gap between the first singlet and triplet excited states (Δ E _ST ) in low‐bandgap acceptors is considered an effective strategy to mitigate this issue. In this work, we design and synthesize a dimeric acceptor, DY‐TXT, utilizing a thermally activated delayed fluorescence (TADF) molecule as the bridging unit. This novel structure exhibits a higher photoluminescence quantum yield and a significantly reduced Δ E _ST (∼0.1 eV) compared to conventional nonfullerene acceptors. When incorporated into the D18:L8‐BO host system, DY‐TXT enhances the electroluminescence quantum efficiency and markedly suppresses triplet exciton generation, thereby reducing energy loss via triplet states. The small Δ E _ST also facilitates reverse intersystem crossing process, enabling recycling of triplet excitons. Consequently, the resulting ternary device achieves a low non‐radiative energy loss of 0.194 eV and an outstanding power conversion efficiency of 20.85%. This work demonstrates an effective strategy for suppressing triplet‐mediated energy losses and provides a promising avenue for advancing the performance of OSCs.

Exciton diffusion length ( L _D ) is a critical parameter for organic solar cells (OSCs). State‐of‐the‐art OSCs are based on Y‐type non‐fullerene acceptor (NFA) materials (including Y6 and its derivatives). Recent studies have revealed that intermolecular charge‐transfer (ICT) excitons are created in Y‐type NFAs, but the precise role of ICT exciton formation on L _D has not been discussed. Here, it is reported that, due to the spectral evolution near the optical gap associated with ICT exciton formation on the picosecond timescale, overlooking this phenomenon may lead to significant overestimation of L _D from transient absorption data analysis for Y‐type NFA films. Moreover, when performing numerical fitting using the exciton‐exciton annihilation model, taking the intrinsic relaxation lifetime of the ICT exciton is essential for the reliable extraction of diffusion coefficient and L _D . Finally, besides showing increasing L _D with reducing π–π stacking spacing, these results show that L _D is defined by the crystalline domain size of the solution‐processed Y‐type NFA films, suggesting that the reported L _D may yet to have reached its fundamental limit. These results provide new insights for achieving long‐range exciton diffusion in OSC materials, paving the way for the realization of highly efficient OSCs with increased domain sizes and film thicknesses.

The commercialization of organic solar cells (OSCs) is limited by bottlenecks including relatively high voltage loss, insufficient donor–acceptor interfacial charge generation, and morphological instability. Traditional approaches of interfacial regulation usually struggle with unmatching energetic landscape and/or molecular compatibility. In this study, two small molecules, L8‐CT and L8‐2CT are designed and synthesized by end‐group substitution of the star nonfullerene acceptor L8‐BO, gradually switching it from electron acceptor to electron donor. Moreover, L8‐2CT with full end‐group substitution exhibits exceptional compatibility/miscibility with both donor (PM6) and acceptor (L8‐BO) in the ternary blend. The tight molecular packing between L8‐2CT and L8‐BO also reduces exciton diffusion time by an order of magnitude compared to PM6:L8‐BO. The introduction of L8‐2CT significantly enhances the donor–acceptor molecular percolation at the interface so that enabling auxiliary charge generation and transport pathways, thereby boosting the interfacial charge generation efficiency and morphology stability. Therefore, the PM6:L8‐BO:L8‐2CT ternary device achieves a remarkable efficiency of 20.33%, with simultaneously enhanced photostability. This achievement fundamentally challenges the traditional design paradigms for third components in ternary OSCs.

The commercialization of organic solar cells (OSCs) is limited by bottlenecks including relatively high voltage loss, insufficient donor–acceptor interfacial charge generation, and morphological instability. Traditional approaches of interfacial regulation usually struggle with unmatching energetic landscape and/or molecular compatibility. In this study, two small molecules, L8‐CT and L8‐2CT are designed and synthesized by end‐group substitution of the star nonfullerene acceptor L8‐BO, gradually switching it from electron acceptor to electron donor. Moreover, L8‐2CT with full end‐group substitution exhibits exceptional compatibility/miscibility with both donor (PM6) and acceptor (L8‐BO) in the ternary blend. The tight molecular packing between L8‐2CT and L8‐BO also reduces exciton diffusion time by an order of magnitude compared to PM6:L8‐BO. The introduction of L8‐2CT significantly enhances the donor–acceptor molecular percolation at the interface so that enabling auxiliary charge generation and transport pathways, thereby boosting the interfacial charge generation efficiency and morphology stability. Therefore, the PM6:L8‐BO:L8‐2CT ternary device achieves a remarkable efficiency of 20.33%, with simultaneously enhanced photostability. This achievement fundamentally challenges the traditional design paradigms for third components in ternary OSCs.

Nonradiative voltage loss (Δ V _nr ) is a critical factor that limits the efficiency of organic solar cells (OSCs). Introducing highly luminescent materials is a promising approach to reduce Δ V _nr . The majority of prior works have focused on enhancing luminescence of low‐bandgap nonfullerene acceptors, whereas highly luminescent donors have received far less attention. Herein, we designed and synthesized a highly luminescent polymer donor with aggregation‐enhanced emission property, namely PiNTSO‐F, and incorporated it into PM6:BTP‐eC9‐based system. Interestingly, PiNTSO‐F was found to locate at the donor–acceptor interface, where it optimizes the interfacial morphology, energetic landscape, and charge dynamics of the active layer. Consequently, the nonradiative recombination rate in the ternary system is significantly reduced, while the interfacial charge generation efficiency is simultaneously improved to nearly unity, effectively minimizing Δ V _nr of the device. As a result, the ternary devices achieve a low Δ V _nr of 0.192 V and a high efficiency of 20.36%. This work demonstrates an effective strategy for suppressing Δ V _nr through developing the highly luminescent polymer donors as a third component, providing mechanistic insights that enable high‐performance OSCs with minimized voltage loss.

Nonradiative voltage loss (Δ V _nr ) is a critical factor that limits the efficiency of organic solar cells (OSCs). Introducing highly luminescent materials is a promising approach to reduce Δ V _nr . The majority of prior works have focused on enhancing luminescence of low‐bandgap nonfullerene acceptors, whereas highly luminescent donors have received far less attention. Herein, we designed and synthesized a highly luminescent polymer donor with aggregation‐enhanced emission property, namely PiNTSO‐F, and incorporated it into PM6:BTP‐eC9‐based system. Interestingly, PiNTSO‐F was found to locate at the donor–acceptor interface, where it optimizes the interfacial morphology, energetic landscape, and charge dynamics of the active layer. Consequently, the nonradiative recombination rate in the ternary system is significantly reduced, while the interfacial charge generation efficiency is simultaneously improved to nearly unity, effectively minimizing Δ V _nr of the device. As a result, the ternary devices achieve a low Δ V _nr of 0.192 V and a high efficiency of 20.36%. This work demonstrates an effective strategy for suppressing Δ V _nr through developing the highly luminescent polymer donors as a third component, providing mechanistic insights that enable high‐performance OSCs with minimized voltage loss.