Synergetic Effect of a Surfactant on the Facile Fabrication and High Detectivity of an Inverted Organic Bulk Heterojunction Photodiode

A new photodiode fabrication strategy for organic photodiodes is proposed, involving the use of a small amount of cationic surfactant in a blend solution aiming at synergetic effects of facile device fabrication and high performances. By adding a small amount of cationic surfactant (cetyltrimethylammonium bromide (CTAB)) to a blend solution consisting of poly(3-hexylthiophene) (P3HT) and phenyl-C61-butyric acid methyl ester (PC60BM), the indium tin oxide (ITO) work function can be reduced to 4.55 eV due to the formation of a CTAB dipole layer, without the insertion of oxide buffer layers. Furthermore, we observe a meaningful contribution of the addition of CTAB to the morphology of the active layer in terms of the intermiscibility between P3HT and PC60BM. Various photophysical, morphological, and structural analyses provided strong evidence for the enhanced intermiscibility between P3HT and PC60BM. Owing to the synergetic contribution of CTAB, the resulting photodiode with inverted diode geometry reveals a high detectivity of similar to 2.5 x 10(12) Jones based on a low dark current of 1.3 x 10(-8) A/cm(2) at 1 V. In addition, a high -3 dB frequency of 4 kHz and a linear dynamic range of 100 dB are demonstrated. This work opens the possibility of facile and simple photodiode patterning/printing processes.