Enhanced electron extraction from solution processed organic solar cells employing rhodamine B doped fullerene layers

•n-Doping of fullerene layers from solution using cationic dyes.•Enhanced electron extraction from nanoparticulate organic solar cells.•Quantitative investigation of excess charge carrier densities.

Fullerene interlayers are a common approach to improve electron extraction in organic solar cells. In this work, we investigate n-doping of solution processed fullerene derivatives by the cationic dye rhodamine B (RhB), formerly known from vacuum device fabrication only. The doping efficiency under illumination is quantified by electron paramagnetic resonance yielding 0.3% for PCBM, and 0.02% for bis-PCBM and ICBA. Incorporated into nanoparticulate organic solar cells, n-doped fullerene layers enhanced the electron extraction and improved the devices' power conversion efficiencies.

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