Diammonium-Cesium Lead Halide Perovskite with Phase-Segregated Interpenetrating Morphology for Photovoltaics

Abstract

The insertion of organic spacers into halide perovskite slabs has offered a trade-off between the efficiency and stability of perovskite solar cells (PSCs). The layered structure of diammonium-intercalated cesium lead halide perovskites is virtually unexplored, in contrast to several works on the monoammonium system. In this report, we find that perovskite with 1,4-butanediammonium (BDA) and cesium cations can only form <i>n</i> = 1 and <i>n</i> = 2 layered isologues defined by the chemical formula of (BDA)Cs_<i>n</i>-1Pb_<i>n</i>(I_0.7Br_0.3)_3<i>n</i>+1, while the <i>n</i> = 3-4 ones will self-construct into unique heterostructures comprising separated quantum wells (QWs; <i>n</i> = 1-2) and 3D (<i>n</i> = ∞) perovskites. We highlight that the 2D/3D heterostructures show a structural resemblance to that of bulk heterojunction in organics, thus improving the charge separation and transport more than surface passivation. Solar cells based on the (BDA)Cs₃Pb₄I_9.1Br_3.9 (<i>n</i> = 4) absorbing layer delivered a power conversion efficiency (PCE) reaching 9.49% with ideal light and thermal stability.