Perovskite solar cells with carbon back contact (C-PSC) represent a promising architecture that allows for a simplification of the manufacture process and a stabilization of the cell performances. In this work, we designed a fully printable C-PSC using a homemade mesoporous alumina (Al 2 O 3) ink. By increasing the alumina layer thickness we show that fill factor reduces, short-circuit current increases, while open circuit voltage increases until a thickness of 1.2 μm. In order to improve performances of PSCs, we investigated a water pre-treatment before perovskite deposition. We show that water pre-treatment improves pore filling, leads to a reduction of charge recombination, and improves the conversion of PbI 2 crystals into perovskite. The water pre-treatment permits to obtain an average efficiency increasing of 16% with respect to cells without water pre-treatment. • Structure's optimization of a Carbon based Perovskite Solar device (C-PSC) with an home-made Al 2 O 3 ink. • Al 2 O 3 thickness optimization as spacing layer in a C-PSC with an optimum at 1.2 μm. • Power Conversion Efficiency (PCE) increment in a C-PSC by a water treatment. • 16% of average increment in water treated cells respects of no-treated cells with a max PCE of 12.3%. • EIS, XRD, LBIC characterizations for deep analysis on water's behaviour. [ABSTRACT FROM AUTHOR]