Crystallization dynamics of MAPbI3 perovskite solar cells via solvent engineering methods

Abstract

Perovskite materials have attracted interest in solar cells due to ease of processing from salts. However, the complex crystal formation of perovskite from solvents is poorly understood. Solvent engineering approach to determine the crystallization dynamics and orientation of MAPbI3 films using grazing incidence wide angle x-ray scattering (GIWAXS) and micro diffraction measurements were studied. The study further probes the effect of moisture, PTAA and PEDOTS: PSS hole transport layers on the stability of MAPbI3 films. Precursor solutions were prepared by dissolving MAI and PbI2 in pure DMF and mixture of DMF: DMSO in 4:1 v/v. Chlorobenzene and Ethyl acetate were used as antisolvent. Films prepared from DMF: DMSO mixture showed no PbI2 signature while those prepared from DMF only, showed PbI2 signature at q= 0.9 A-1. This was attributed to solvent engineering of DMF/DMSO that leads to the formation of MAI/PbI2/DMSO intermediate that delays the crystallization and promotes vertical growth of films. q= 0.9 A-1 signal was associated with high volatility of DMF which led to faster but discrepant nucleation and crystallization rate. Microdiffraction results showed insignificant influence of antisolvent on the perovskite structure. Humidity has a strong influence on the stability of MAPbI3 films. PbI2 intensity in the GIWAXS maps increased with increasing humidity while MAPbI3 intensity decreased. This implied increased degradation of MAPbI3 film with humidity due to recombination of charge carriers. A band gap of 1.57 eV, efficiency of 8.5% and Et of 26 meV were obtained. Films with good crystallization are desirable in solar cells.