Thickness effects of thermally evaporated C60 thin films on regular-type CH3NH3PbI3 based solar cells

- The structural properties of C60 films were studied by the Raman and PL spectra.
- The conduction band minimum of the C60 film is dependent on the thickness.
- The C60 has a hydrophilic nature when the thickness is smaller than 10 nm.
- The coverage of CH3NH3PbI3 on the C60 dominates the fill factor of the solar cell.

Comprehensive studies were carried out to explore the thickness-dependent characteristics of thermally evaporated C60 thin films. The structural, optical, electronic and surface properties of the resultant C60 thin films were analyzed using Raman scattering spectrometry, photoluminescence spectroscopy, absorbance spectroscopy, photoelectron emission spectrometry and water droplet contact angle measurement. The experimental results show that the thickness of the C60 thin film has a decisive impact on the photovoltaic performance of CH3NH3PbI3 based solar cells in terms of open-circuit voltage (VOC), short-circuit current density (JSC) and fill factor (FF). In the case of the 2.5 nm-thick C60 film, the solar cells have the better VOC and JSC, as the results of the lower electron affinity and higher transparency. The FF of the solar cell is related to the coverage of C60 on the transparent conductive electrode (TCE) and the CH3NH3PbI3 perovskite continuity. Consequently, the photovoltaic performance can be expected to be improved by using a smooth TCE.

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