Organic spacer engineering of Ruddlesden-Popper perovskite materials toward efficient and stable solar cells

Organic spacers in the Ruddlesden-Popper perovskite (RPP) materials significantly enhance the operating sta-bility of the corresponding solar cells, but limit their devices performance owing to inefficient charge transport. Inspired by 3D perovskites, binary spacer-based RPP devices show great potential in outperforming their unary spacer counterparts, yet it still lacks the rational design of RPP materials based on binary spacer from a molecular level to tune optoelectronic properties and device performance. Therefore, several novel binary spacer RPP films (F-PEA1-xGAx)2MA3Pb4I13 (x <= 0.3, F-PEA = 4-fluorophenethylammonium, GA = guanidinium, MA = methyl -ammonium) are prepared to investigate the impact of binary spacer on film properties and device performance. By incorporating 20 % GA into F-PEA2MA3Pb4I13, the as-prepared film becomes smoother with superior vertical alignment and larger-sized crystal grains, yielding an obvious reduction of trap density and better hole mobility, which more effectively inhibits the nonradiative recombination and accelerates the hole extraction. Conse-quently, an optimal efficiency of 17.50 % is achieved for the (F-PEA0.8GA0.2)2MA3Pb4I13 based device, among the highest values for binary spacer RPP (n <= 5) solar cells reported to date. Additionally, this device maintains 87 % and 90 % of its starting efficiency after 500 aging hours in ambient air and 1000 h tracking at the maximum power point under illumination, respectively.