• Energy Research

A new hybrid strategy synthesizes the TQT acceptor with thiadiazole and quinoxaline units. The resulting TQT-based OSC achieved 18.52% efficiency, topping linear trimer acceptor-based OSCs, while also exhibiting robust stability.

We synthesized three fluorinated non-fullerene acceptors, BTP-F, Y6-F and L8-BO-F, and further used them as the third components to fabricate ternary organic solar cells. The PM6:BTP-eC9:BTP-F ternary device yielded a high efficiency of 18.45%.

Molecular design of non-fullerene acceptors is of vital importance for high-efficiency organic solar cells. The branched alkyl chain modification is often regarded as a counter-intuitive approach, as it may introduce an undesirable steric hindrance that reduces charge transport in non-fullerene acceptors. Here we show the design and synthesis of a highly efficient non-fullerene acceptor family by substituting the beta position of the thiophene unit on a Y6-based dithienothiophen[3,2-b]-pyrrolobenzothiadiazole core with branched alkyl chains. It was found that such a modification to a different alkyl chain length could completely change the molecular packing behaviour of non-fullerene acceptors, leading to improved structural order and charge transport in thin films. An unprecedented efficiency of 18.32% (certified value of 17.9%) with a fill factor of 81.5% is achieved for single-junction organic solar cells. This work reveals the importance of the branched alkyl chain topology in tuning the molecular packing and blend morphology, which leads to improved organic photovoltaic performance. Molecular design of acceptor and donor molecules has enabled major progress in organic photovoltaics. Li et al. show that branched alkyl chains in non-fullerene acceptors allow favourable morphology in the active layer, enabling a certified device efficiency of 17.9%.

Ferrocene was introduced as a solid additive in organic solar cells (OSCs). The use of ferrocene provides PM6:Y6 based device with improved performance and stability, demonstrating its great potential in the fabrication of efficient and stable OSCs.

A series of high fluorescence triphenylamine halides are proposed as solid additives to reduce the static disorder and thus improve the luminescence performance of the active layer to suppress non-radiative recombination loss.

AbstractTwo donor–acceptor (D–A) type conjugated copolymers, P1 and P2, are designed and synthesized. A classical benzothiadiazole acceptor is used to replace a thiophene unit in the polymer chain of P1 to obtain P2 terpolymer. Compared with P1, P2 exhibits broader absorption spectra, higher absorption coefficient, deeper lowest unoccupied molecular orbital level, and a relatively lower band gap. As a result, the P2‐based solar cell exhibits a high power conversion efficiency (PCE) of 6.60%, with a short‐circuit current (J sc) of 12.43 mA cm−2, and a fill factor (FF) of 73.1%, which are higher than those of the P1‐based device with a PCE of 4.70%, a J sc of 9.43 mA cm−2, and an FF of 61.6%.

The introduction of halogen atoms in the donor molecules in organic solar cells leads to a decrease in the reorganization energy, which in turn results in reduced non-radiative voltage losses and an improved open-circuit voltage in the devices.

Recent advances in organic solar cells based on non-fullerene acceptors (NFAs) come with reduced non-radiative voltage losses (ΔVnr). Here we show that, in contrast to the energy-gap-law dependence observed in conventional donor:fullerene blends, the ΔVnr values in state-of-the-art donor:NFA organic solar cells show no correlation with the energies of charge-transfer electronic states at donor:acceptor interfaces. By combining temperature-dependent electroluminescence experiments and dynamic vibronic simulations, we provide a unified description of ΔVnr for both fullerene- and NFA-based devices. We highlight the critical role that the thermal population of local exciton states plays in low-ΔVnr systems. An important finding is that the photoluminescence yield of the pristine materials defines the lower limit of ΔVnr. We also demonstrate that the reduction in ΔVnr (for example, <0.2 V) can be obtained without sacrificing charge generation efficiency. Our work suggests designing donor and acceptor materials with high luminescence efficiency and complementary optical absorption bands extending into the near-infrared region. Organic solar cells based on non-fullerene acceptors have enabled high efficiencies yet their charge dynamics and its impact on the photovoltaic parameters are not fully understood. Now, Chen et al. provide a general description of non-radiative voltage losses in both fullerene and non-fullerene solar cells.