A new non-fullerene acceptor, named N3, was developed by using a 3 rd -position branched alkyl chain on the pyrrole motif of the molecule, which yielded better performance than the state-of-the-art acceptor Y6. Ternary devices were fabricated, achieving a power conversion efficiency of 16.74% in the lab and a certified efficiency of 16.42% by Newport.

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flexibility, and tunable optical transparency, which are advantageous for applications in building-integrated photovoltaic (PV) and wearable electronics compared with conventional inorganic cells. [1][2][3][4][5] To achieve high efficiency, it is essential to develop suitable donor (D) and acceptor (A) materials that can be easily processed into a finely phase-separated morphology in active layer with low energy loss (E loss ) in OSCs. [6][7][8][9] Recently, the vibrant progress made on nonfullerene acceptors (NFAs), [10,11] especially the Y-series NFAs, [12] with facilely tailored chemical structures and precisely tuned bandgap, energy levels, and crystallization properties, has enabled OSCs to achieve very high power conversion efficiencies (PCEs) ≈19%. [13][14][15][16][17][18][19][20][21][22][23][24][25][26][27][28][29][30][31][32] The bulk-heterojunction (BHJ) architecture-based devices prepared from mixing D and A in solution is the most widely adopted method for depositing photoactive layer and have successfully increased the PCE of single-junction OSCs to 19% recently. [31] Another emerging strategy is to deposit neat D and A materials A record power conversion efficiency (PCE) of over 19% is realized in planarmixed heterojunction (PMHJ) organic solar cells (OSCs) by adopting the asymmetric selenium substitution strategy in making a pseudosymmetric electron acceptor, BS3TSe-4F. The combined molecular asymmetry with more polarizable selenium substitution increases the dielectric constant of the D18/ BS3TSe-4F blend, helping lower the exciton binding energy. On the other hand, dimer packing in BS3TSe-4F is facilitated to enable free charge generation, helping more efficient exciton dissociation and lowering the radiative recombination loss (ΔE 2 ) of OSCs. As a result, PMHJ OSCs based on D18/BS3TSe-4F achieve a PCE of 18.48%. By incorporating another mid-bandgap acceptor Y6-O into D18/BS3TSe-4F to form a ternary PMHJ, a higher open-circuit voltage (V OC ) can be achieved to realize an impressive PCE of 19.03%. The findings of using pseudosymmetric electron acceptors in enhancing device efficiency provides an effective way to develop highly efficient acceptor materials for OSCs.

This research provides a structure-property relation that sheds light on morphological stability of NF-OSCs by using the thermodynamic and the kinetic perspectives. We show that NF-OSCs can suffer from excessive amorphousamorphous phase separation in the blends and crystallization of NF-SMA. The former instability channel can be eliminated in systems with an optimal miscibility, whereas the excessive phase separation in low miscibility systems and NF-SMA crystallization need to be suppressed through the utilization of polymers or NF-SMAs with low flexibility.

Some fundamental questions in the organic solar cell (OSC) community are related to the role of bulk and interfacial morphology on key processes such as charge generation, recombination, and extraction...

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In this paper, a strategy of asymmetric alkyl and alkoxy substitution is applied to state‐of‐the‐art Y‐series nonfullerene acceptors (NFAs), and it achieves great performance in organic solar cell (OSC) devices. Since alkoxy groups can have a significant influence on the material properties of NFAs, alkoxy substitution is applied to the Y6 molecule in a symmetric manner. The resulting molecule (named Y6‐2O), despite showing improved open‐circuit voltage (Voc), yields extremely poor performance due to low solubility and excessive aggregation properties, a change that is due to the conformational locking effect of alkoxy groups. In contrast, asymmetric alkyl and alkoxy substitution on Y6, yields a molecule named Y6‐1O that can maintain the positive effect of Voc improvement and obtain reasonably good solubility. The resulting molecule Y6‐1O enables highly efficient nonfullerene OSCs with 17.6% efficiency and the asymmetric side‐chain strategy has the potential to be applied to other NFA‐material systems to further improve their performance.

Solution-processed organic solar cells (OSCs) are a promising candidate for next-generation photovoltaic technologies. However, the short exciton diffusion length of the bulk heterojunction active layer in OSCs strongly hampers the full potential to be realized in these bulk heterojunction OSCs. Herein, we report high-performance OSCs with a pseudo-bilayer architecture, which possesses longer exciton diffusion length benefited from higher film crystallinity. This feature ensures the synergistic advantages of efficient exciton dissociation and charge transport in OSCs with pseudo-bilayer architecture, enabling a higher power conversion efficiency (17.42%) to be achieved compared to those with bulk heterojunction architecture (16.44%) due to higher short-circuit current density and fill factor. A certified efficiency of 16.31% is also achieved for the ternary OSC with a pseudo-bilayer active layer. Our results demonstrate the excellent potential for pseudo-bilayer architecture to be used for future OSC applications.