Structural, optical and excitonic properties of urea grading doped CH3NH3PbI3 thin films and their application in inverted-type perovskite solar cells.

—The structural, optical and excitonic characteristics of urea doped CH 3 NH 3 PbI 3 (MAPbI 3) multi-crystalline thin films were investigated by using the X-ray diffraction patterns, atomic-force microscopic images, absorbance spectra, photoluminescence (PL) spectra and Raman scattering spectra. The surface-sensitive Raman scattering spectra show that the urea small molecules are mainly distributed in the top region of the MAPbI 3 thin films and thereby effectively passivating the electron-poor defects (interfacial MA cations) of MAPbI 3 thin films. Besides, the thermal annealing temperature and the concentration of urea additive both strongly influence the formation of MAPbI 3 thin films, which dominates the photovoltaic performance. The use of 5-wt% urea can increase the open-circuit voltage (V OC) and short-circuit current density (J SC) of the MAPbI 3 solar cells from 0.88 V to 19.75 mA/cm2 to 0.94 V and 22.97 mA/cm2, respectively. In addition, the reduced current hysteresis in the J-V curves of the MAPbI 3 solar cells can be explained as due to the effective defect passivation in the top region of the MAPbI 3 thin film by the oxygen-donors of the urea small molecules. Image 1 • The optoelectronic properties of urea-doped MAPbI 3 thin films are investigated. • The 5-wt% urea-doped MAPbI 3 thin film has the disk-like shaped grains. • The urea small molecules are mainly distributed in the top region of MAPbI3 thin films. • The V OC and J SC of MAPbI3 solar cells are simultaneously increased by using the urea additive. [ABSTRACT FROM AUTHOR]