High Open-Circuit Voltage Organic Solar Cells with 19.2% Efficiency Enabled by Synergistic Side-Chain Engineering.

Restricted by the energy-gap law, state-of-the-art organic solar cells (OSCs) exhibit relatively low open-circuit voltage (VOC; 0.8-0.9 V) because of large nonradiative energy losses. Moreover, the trade-off between VOC and external quantum efficiency (EQE) of OSCs is more distinctive; the power conversion efficiencies (PCEs) of OSCs are still < 15% with VOCs of > 1.0 V. Herein, we carefully consider the electronic properties and aggregation behaviors of non-fullerene acceptors (NFAs) and then delicately design a new NFA (Z19) by simultaneously introducing alkoxy and phenyl-substituted alkyl chains to the conjugated backbone. Z19 exhibits a hypochromatic-shifted absorption spectrum and a high-lying LUMO energy level. Moreover, Z19 presents an ordered two-dimensional packing mode and good miscibility with polymer donor D18. The blend film exhibits suitable crystallinity and favorable phase separation with face-on dominated molecular orientation, facilitating charge transport properties. Consequently, D18:Z19 binary devices afford an exciting PCE of 19.2% (certified 18.8%) with a high VOC of 1.002 V and an EQEmax of 91.4%, much higher than for Y6-2O-based devices (PCE = 4.85%). (The latter is the highest PCE reported to date for OSCs with VOCs of > 1.0 V.) Moreover, the nonradiative energy losses of Z19-based (0.200 eV) and Y6-2O-based (0.155 eV) devices are much lower than that of Y6-based (0.239 eV) devices. Indications are that the design of such NFA organic semiconductors, considering the energy-gap law, could promote a new breakthrough in OSCs. This article is protected by copyright. All rights reserved.