Organic phototransistors with nanoscale phase-separated polymer/polymer bulk heterojunction layers

Abstract

Low-cost detectors for sensing photons at a low light intensity are of crucial importance in modern science. Phototransistors can deliver better signals of low-intensity light by electrical amplification, but conventional inorganic phototransistors have a limitation owing to their high temperature processes in vacuum. In this work, we demonstrate organic phototransistors with polymer/polymer bulk heterojunction blend films (mixtures of p-type and n-type semiconducting polymers), which can be fabricated by inexpensive solution processes at room temperature. The key idea here is to effectively exploit hole charges (from p-type polymer) as major signaling carriers by employing p-type transistor geometry, while the n-type polymer helps efficient charge separation from excitons generated by incoming photons. Results showed that the present organic transistors exhibited proper functions as p-type phototransistors with ∼4.3 A W(-1) responsivity at a low light intensity (1 µW cm(-2)), which supports their encouraging potential to replace conventional cooled charge coupled devices (CCD) for low-intensity light detection applications.

Organic Phototransistors With All-Polymer Bulk Heterojunction Layers of p-Type and n-Type Sulfur-Containing Conjugated Polymers

“…The apparent responsivity was remarkably enhanced for all three wavelengths as the incident light intensity decreased (see Fig. 4(a) left), which supports the reduced charge recombination at low light intensity in the case of BHJ channel layers [51], [52]. The logarithmic plot (see Fig.…”

“…BHJ layers consisting of n-type (electron-accepting) and p-type (electrondonating) polymers may be preferable for improved flexibility, and to control phase segregation. We have previously reported devices of this type, composed of poly(9, 9-dioctlyfluorene-cobenzothiadiazole) (F8BT; n-type) and poly(3-hexylthiophene) (P3HT; p-type) [52]. However, the F8BT in these all-polymer phototransistors has a relatively wide optical gap (∼2.4 eV) such that its absorbance doesn't enhance the long wavelength response beyond that of P3HT.…”

Efficient optical gain media comprising binary blends of poly(3-hexylthiophene) and poly(9,9-dioctylfluorene-co-benzothiadiazole)

“…% RR-P3HT, the thresholds rise rapidly, again consistent with the more favourable photocharge generation in RR-P3HT/F8BT blends for higher polythiophene loadings. 37,38 This competing process decreases the exciton population available for gain and the resulting charge states can also act efficiently as catalytic (i.e., not themselves quenched) exciton quenching sites. 47 Fig.…”

“…%), 37 and the same composition was used for phototransistors. 38 Conversely, for LEDs, performance is optimised at a lower concentration, namely $10-20 wt. % RR-P3HT.…”

Polymer–Fullerene Bulk Heterojunction-Based Strain-Sensitive Flexible Organic Field-Effect Transistor

“…Rootmean-square (RMS) roughness value of the active layer was found to be equal to 4.34 nm. Energy bands are shown as [21,22], but there is an energy difference of around 1eV between the work function of Ag and LUMO level of PCBM (−3.7 eV). Therefore, holes can easily be injected into the active layer from drain/source electrodes as compared to electrons.…”