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The averaged power conversion efficiency of polyelectrolytes (P3CT-Na) based MAPbI3 solar cells can be increased from 14.94% to 17.46% with a wetting method before the spin-coating process of MAPbI3 precursor solutions. The effects of the wetting process on the surface, structural, optical and excitonic properties of MAPbI3 thin films are investigated by using the atomic-force microscopic images, x-ray diffraction patterns, transmittance spectra, photoluminescence spectra and Raman scattering spectra. The experimental results show that the wetting process of MAPbI3 precursor solution on top of the P3CT-Na/ITO/glass substrate can be used to manipulate the molecular packing structure of the P3CT-Na thin film, which determines the formation of MAPbI3 thin films. [ABSTRACT FROM AUTHOR]

A series of alcohols (methanol, ethanol and isopropyl alcohol) were added to poly(3,4-ethylenedioxythiophene): (polystyrene sulfonate) (PEDOT: PSS) aqueous solutions in order to manipulate the molecular structure of the PEDOT chains in PEDOT: PSS hole transporting materials (HTMs) and thus to improve the power conversion efficiency of CH 3 NH 3 PbI 3 based solar cells. The structural and electronic characteristics of the resultant PEDOT: PSS HTMs were analyzed using atomic-force microscopy, contact angle measurement, Raman scattering spectrometry and photoelectron spectrometry. The properties of the PEDOT: PSS thin films could be controlled by tuning the viscosity of the PEDOT: PSS solutions. High viscosity PEDOT: PSS solutions resulted in linear structured PEDOT chains, which increased the work function of the PEDOT: PSS HTMs thereby improving the open-circuit voltage of the CH 3 NH 3 PbI 3 solar cells. The surface roughness and surface free energy of the PEDOT: PSS HTMs influence the structural properties of CH 3 NH 3 PbI 3 thin films, which determines the exciton dissociation at the CH 3 NH 3 PbI 3 /PEDOT: PSS interface (short-circuit current density) and the carrier recombination at the CH 3 NH 3 PbI 3 /[6,6]-phenyl-C61-butyric acid methyl ester (PC 61 BM) interface (fill factor). In addition, it is predicted that the power conversion efficiency can be further improved by increasing the crystallinity of the CH 3 NH 3 PbI 3 thin film. [ABSTRACT FROM AUTHOR]

Transmittance spectra, atomic-force microscopic images, energy-dispersive X-ray spectra and droplet contact angle images show that a facile wet etching process can be used to manipulate the thickness, surface roughness, surface chemical composition and surface wettability of the indium-tin oxide (ITO) thin films, which influences the molecular packing structure of the P3CT-Na thin films and thereby dominating the crystal quality of the CH 3 NH 3 PbI 3 (MAPbI 3) thin films. The power conversion efficiency (PCE) of the P3CT-Na based MAPbI 3 solar cells can be improved from 17.02% to 19.35% by increasing the Sn/In concentration ratio of the ITO thin films from 0.36 to 0.47 with a facile wet etching process at a constant temperature of 40 °C. It is noted that the PCE of the optimal solar cell decreases slowly toward a stable PCE of 16% for more than 60 days under moderate environment conditions (55 ± 10 RH%). • Surface properties of the ITO/glass substrates can be varied by the wet etching process. • The contact quality at the P3CT-Na/ITO interface can be improved. • The contact quality at the MAPbI3/P3CT-Na interface can be improved. • After 60 days, the PCE slowly decreased from 19.35% to 16.03%. [ABSTRACT FROM AUTHOR]