Enhanced crystallinity of CH(3)NH(3)PbI(3) by the pre-coordination of PbI(2)–DMSO powders for highly reproducible and efficient planar heterojunction perovskite solar cells

Solution processable CH(3)NH(3)PbI(3) has received considerable attention for highly-efficient perovskite solar cells. However, the different solubility of PbI(2) and CH(3)NH(3)I is problematic, initiating active solvent engineering research using dimethyl sulfoxide (DMSO). Here we investigated the pre-coordination of PbI(2)–DMSO powders for planar heterojunction perovskite solar cells fabricated by a low-temperature process (≤100 °C). Pre-coordination was carried out by simple mechanical mixing using a mortar and pestle. The composition of PbI(2)–DMSO(x) (x = 0, 1, or 2) in the powder mixture was investigated by gradually increasing mechanical mixing time, and a dominant composition of PbI(2)–DMSO(1) was obtained after a 10 min mixing process. The pre-coordinated PbI(2)–DMSO powders were then blended with CH(3)NH(3)I in DMF to make the CH(3)NH(3)PbI(3) film by toluene-assisted spin-coating and heat treatment. Compared with the one-step blending of CH(3)NH(3)I, PbI(2), and DMSO in DMF, the pre-coordination method resulted in better dissolution of PbI(2), larger grain size, and pinhole-free morphology. Consequently, absorption, fluorescence, carrier lifetime, and charge extraction were enhanced. The average open-circuit voltage (1.046 V), short-circuit current (22.9 mA cm(−2)), fill factor (73.5%), and power conversion efficiency (17.6%) were increased by 2–12% with decreased standard deviations (13–50%), compared with the one-step blending method. The best efficiency was 18.2%. The simple mechanical pre-coordination of PbI(2)–DMSO powders was very effective in enhancing the crystallinity of CH(3)NH(3)PbI(3) and photovoltaic performance.