Effect of Device Structure on the Narrow-band Light Detection of Bulk Heterostructure Organic Photodetectors based on Poly(3-hexylthiophene) and Fullerene Derivative

The characteristics of organic photodetectors based on poly(3-hexylthiophene) (P3HT) and [6,6]-phenyl C61-butyric acid methyl ester (PCBM) blends with various film thicknesses of active layer are investigated. The red-shift in peak wavelength of incident-photon-to-current conversion efficiency (IPCE) spectra in the devices with various film thicknesses is observed with increasing film thickness. For thick devices upon irradiation by light with a photon energy of around energy gap of an active layer, excitons are formed almost uniformly because of the small absorption coefficient of red light. A conventional device with 2 μm-thick film exhibits narrow-band light detection with red-light sensitivity and the relatively narrow spectral response of the full-width at half-maximum (FWMH) of around 50 nm. On the other hand, an inverted device with 2 μm-thick film exhibits broadband light detection. For bulk heterostructure devices, one of important factors to realize the narrowband light detection is the control of charge carrier collection efficiency at electrodes which is attributed to the device structure, including the intrachain transport in polymer.