Fig. 1From: Perovskite Solar Cells Fabricated by Using an Environmental Friendly Aprotic Polar Additive of 1,3-Dimethyl-2-imidazolidinone a Fourier transform infrared transmittance spectra of DMF and PbI2∙DMF. b Fourier transform infrared transmittance spectra of DMI and PbI2∙DMI. c Thermal gravimetric analysis of the PbI2 Lewis adducts. d XRD curves of the Lewis adducts of PbI2∙DMI and PbI2∙DMFBack to article page