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 stability 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 = methylammonium) 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. Consequently, 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.