The new era for organic solar cells: non-fullerene small molecular acceptors

Organic solar cells (OSCs) is a promising renewable energy technology as their prospect in producing large-area photovoltaic modules via low-cost roll-to-roll processing and their widespread application including photovoltaic farms, building integration, and portable electronics, etc. [1]. The key component of an OSC is its photoactive layer, which is a bulk-heterojunction blend of an electron donor and an electron acceptor [2]. The electron donors are p-type semi-conducting conjugated polymers or small molecules, and the electron acceptors were predominated by fullerene derivatives in OSC history. The power conversion efficiencies (PCEs) of fullerene-based OSCs have been promoted to ≈11% via ~20 years of effort by researchers all over the world [3]. After that, the fullerene-based OSCs have encountered bottlenecks in both device performance and stability due to the intrinsic drawbacks of fullerene acceptors including poor light-harvesting ability, difficulty in energy level control, and photon-induced dimerization, etc.