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

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 n = 1 and n = 2 layered isologues defined by the chemical formula of (BDA)Csn-1Pbn(I0.7Br0.3)3n+1, while the n = 3-4 ones will self-construct into unique heterostructures comprising separated quantum wells (QWs; n = 1-2) and 3D (n = ∞) 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)Cs3Pb4I9.1Br3.9 (n = 4) absorbing layer delivered a power conversion efficiency (PCE) reaching 9.49% with ideal light and thermal stability.