C.-Z. Li, H. Chen and co-workers present, on page 9729, for the first time, efficient non-fullerene tandem organic solar cells (OSCs) by utilizing all non-fullerene acceptor-based bulk heterojunctions as sub-cells. A high power conversion efficiency of 8.48% is achieved with an ultra-high open-circuit voltage of 1.97 V, which is the highest voltage value reported to date feasible for water splitting among the efficient tandem OSCs.