Energy loss within organic solar cells (OSCs) is undesirable as it reduces cell efficiency 1-4. In particular, non-radiative recombination loss 3 and energetic disorder 5 , which are closely related to the tail states below the band edge and the overall photon energy loss, need to be minimized to improve cell performance. Here, we report how the use of a small-molecule acceptor with torsion-free molecular conformation can achieve a very low degree of energetic disorder and mitigate energy loss in OSCs. The resulting single-junction OSC has an energy loss due to non-radiative recombination of just 0.17 eV and a high power conversion efficiency of up to 16.54% (certified as 15.89% by the National Renewable Energy Laboratory). The findings take studies of organic photovoltaics deeper into a new regime, beyond the limits of energetic disorder and large energy offset for charge generation. Recent developments in organic/polymer bulk heterojunction solar cells (OSCs/PSCs) have led to tremendous advances in power conversion efficiency (PCE), with current leading certified efficiencies of over 15-16% for single-junction devices 6-9 and over 17% for multi-junction devices 10. However, the PCEs of OSCs still lag behind their inorganic semiconductors and perovskite counterparts, in most part due to the modest open-circuit voltage (V OC) imposed by the relatively large photon energy loss 1-4. The photon energy loss in solar cells, ΔE loss ¼ E g � qV OC I (q is the elementary charge, E g is the optical gap of the absorber; Fig. 1), represents the lower limit of energy loss during conversion of photon energy to electrical potential. So far, the best performing inorganic crystalline solar cells show a lower ΔE loss in gallium arsenide (0.32 eV) and crystalline silicon (0.38 eV) 11 , while most of the highly efficient perovskite solar cells have a ΔE loss in the range of 0.4−0.5 eV (ref. 4). Recently, there has been rapid progress in the reduction of photon energy loss in high-performance perovskite solar cells, leading to a record value of 0.34 eV (ref. 12). In contrast, state-of-the-art OSCs usually suffer from high ΔE loss in the range of 0.6−1.1 eV (ref. 13), which is much higher than the theoretical value of 0.25−0.30 eV predicted by Shockley-Queisser (SQ) theory 14. This is because of the relatively high radiative recombination loss due to absorption edge broadening effects 4 and the strong non-radiative recombination loss 1,2,15. Hence, it is clear that further improvement of V OC in OSCs requires a significant reduction of both radiative and non-radiative recombination loss. Although there is no intuitively simple approach to reduce the overall photon energy loss in OSCs, the energetic disorder 5 , which

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A new category of deep-absorbing small molecules is developed. Optimized devices driven by mixed additives show a remarkable short-circuit current of ≈20 mA cm(-2) and a highest power conversion efficiency of 9.06%. A multi-length-scale morphology is formed, which is fully characterized by resonant soft X-ray scattering, high-angle annular dark film image transmission electron microscopy, etc.

Despite the rapid developments in all‐polymer solar cells (all‐PSCs) due to the progress of polymerized small molecular acceptors (PSMA), the effect of linkage unit conjugation on the polymer acceptor (PA) is not well understood and PAs with high efficiency, good stability, and thickness‐insensitivity are rarely seen. Herein, two novel PSMAs, named PJTVT and PJTET are designed, by incorporating conjugated thienylene‐vinylene‐thienylene (TVT) and unconjugated thienylene–ethyl–thienylene (TET) units, respectively. Results show that the energy levels, energy losses, and energy offset of the two PSMAs have little difference (<≈0.03 eV). However, due to the π‐extended coplanar backbone of PJTVT, when blended with polymer donor JD40, a more ordered π–π stacking and enhanced face‐on orientation morphology is observed, which contributes to enhanced exciton dissociation, superior charge transport, and faster charge extraction, leading to a record power conversion efficiency of 16.13% (10.93% for JD40:PJTET). Impressively, the JD40:PJTVT device shows superior thickness‐insensitivity and long‐term stability, both of which make it an ideal choice for industrialization. These results demonstrate that molecular modulation in the linking unit is a promising strategy to construct PSMAs for high‐performance thick‐film all‐PSCs with superior long‐term stability, and shows the superiority of conjugated backbones for PSMAs.