Reliability of all printed polymer photosensors for high illuminance detection

Abstract

An all-printed polymer light sensor was developed for limited use in blast exposure monitoring of soldiers deployed in the battlefield and help with diagnosis of blast-related injuries which include traumatic brain injury (TBI). The sensor was designed for a medical monitoring system capable of collecting information for daily medical records. Due to the harsh environmental conditions, the sensors are designed to be of limited use and adhered directly to objects including non-planar surfaces. This requires that the development of light sensors with transparent top electrodes, high light intensity response and process compatibility with flexible substrates. All layers of the light sensor were fabricated by ink-jet printing. The all-printed light sensor is based on a blend of hole-accepting and electron-accepting derivatives of poly(9,9-dioctylfluorene-co-bis-N,N-(4-butylphenyl)-bis-N,N-phenyl-1,4-phenylenediamine) (PFB) and poly(9,9-dioctylfluorene-co-benzothiadiazole) (F8BT), respectively. The surface of the PFB-F8BT organic photoactive layer is hydrophobic and represents a challenge when fabricating top light-absorbing devices from solution. We solved this fabrication challenge by using a modified formulation of poly(3,4-ethylenedioxythiophene): poly(styrenesulfonate) (PEDOT:PSS) as the top electrode. Sensors were calibrated for high illuminance detection (100 400 klux) and calibration reliability was tested after their intended one week scope of use. The photosensors show good linearity over multiple measurements at high illuminance values of (100 to 400) klux. Calibration reliability data will be presented along with photodiode measurements and printed morphology effects.