Synchronous enhancement of responsivity, response time and, spectral range in solution processed CdS photodetector upon modification with PEDOT:PSS

Solution processed photodetectors with high responsivities and simple fabrication schemes are high on demand for variety of emerging opto-electronic applications. However, these devices suffer from sluggish response and recovery times. In this work, we demonstrate the simultaneous enhancement of the responsivity, response time and spectral range of detection in a solution-processed device based on organic/inorganic hybrid junction. A solution-processed flexible CdS photodetector is fabricated using a facile and economical chemical bath deposition technique. The fabricated pristine-CdS device exhibits responsivity and response time of 50 mA/W and 5.4 s. The resultant device exhibits enhanced responsivity and response time of around 740 mA/W and 0.6 s, respectively, upon modification with the PEDOT:PSS conducting polymer. These values of PEDOT-modified device are one order larger than pristine-CdS detector. Further, PEDOT:PSS modification also extends the responsivity of the device from UV-Vis to NIR spectra. NIR responsivity in the hybrid device, is imputed to the photothermal property of the PEDOT:PSS layer. Thus, the overall device spectral response is accredited to the simultaneous existence of photoelectric and photo-thermal phenomena. The observed responsivity and faster response time is ascribed primarily to the built-in potential at interface of CdS-PEDOT:PSS, which not only facilitates efficient separation of photo carriers but also leads to a reduction in the recombination of excitons. Given the simple approach and excellent enhancement in the device performance, the idea demonstrated here could be useful to design high performance opto-electronic device based on solution-processed techniques.