Semitransparent organic solar cells with organic wavelength dependent reflectors

Semitransparent organic solar cells employing solution-processable organic wavelength dependent reflectors of chiral nematic (cholesteric) liquid crystals are demonstrated. The cholesteric liquid crystal (CLC) reflects only in a narrow band of the solar spectrum and remains transparent for the remaining wavelengths. The reflective band is matched to the absorption spectrum of the organic solar cell such that only unabsorbed photons that can contribute to the photocurrent are reflected to pass through the active layer a second time. In this way, the efficiency of semitransparent organic solar cells can be enhanced without significant transparency losses. An efficiency increase of 6% was observed when a CLC reflector with a reflection band of 540–620 nm was used, whereas the transparency of the organic solar cells is only suppressed in the 80 nm narrow bandwidth.