A novel chain-like conjugated donor-π-acceptor molecular additive for highly efficient and stable perovskite solar cells

In donor-π-acceptor (D-π-A) molecules, the coordination ability of the acceptor can be enhanced by the directed movement of delocalized electrons (DEs) on the π-bridge. However, the conventional aromatic ring as π-bridge limits the number of DEs due to the structural characteristic, which restrict the coordination ability of the acceptor, and there is still a lack of research on this issue. Herein, we proposed a chain-like conjugated π-bridge design strategy to address this issue. The Astaxanthin with eleven contiguous C-C = C fragments was selected as a chain-like D-π-A additive for perovskite films. Twenty-two DEs in such chain-like bridge can move towards the C = O group by the D-π-A effect within Astaxanthin, which increases the electron cloud density of C = O group so that enhances its coordination capacity with cations. Ultimately, the Astaxanthin-based device achieved a champion power conversion efficiency (PCE) of 24.43 % and maintained more than 95 % and 91 % of initial PCE for aging 1000 h in dry air (RH < 1 %) and atmosphere (RH = 20 ∼ 30 %), respectively. This work provides a novel strategy to break the restriction of aromatic rings to DEs, which provides theoretical and experimental guidance for further designing chain-like D-π-A additives with strong defect passivation ability to boost photovoltaic performance of PSCs.