Room temperature preparation of δ-phase CsSn 1−x Pb x I 3 films for hole–transport in solid-state dye-sensitized solar cells

CsSn1−xPbxI3 films were prepared from mixed CsI, SnI2 and/or PbI2 solutions at five different Pb/Sn ratios (x = 0, 0.2, 0.5, 0.8 and 1) at room temperature. The color of the CsSn1−xPbxI3 films varied with their Pb/Sn ratios. At a Pb/Sn ratio of 0.5, CsSn0.5Pb0.5I3 had the darkest color, whereas films at other Pb/Sn ratios displayed dark brown or yellowish colors. The XRD spectra of the as-prepared CsSn1−xPbxI3 films matched the δ-phase (yellow-phase) nonperovskite structure quite well. Solid-state dye-sensitized solar cells (S-DSSCs) were assembled by directly dropping the mixed CsI, SnI2 and/or PbI2 solution onto TiO2-coated-dye electrodes and drying them at room temperature. A CsSn0.5Pb0.5I3 based S-DSSC generated the highest efficiency (3.47%) of the five conditions (CsSn1−xPbxI3, x = 0, 0.2, 0.5, 0.8 and 1). This is attributed to the dark color and good continuity of the CsSn0.5Pb0.5I3 film, its high shunt-resistance (10,377.10 Ω) and high incident-photon collecting efficiency of CsSn0.5Pb0.5I3 based S-DSSCs.