IEEE PHOTONICS TECHNOLOGY LETTERS, VOL. 29, NO. 20, OCTOBER 15, 2017 1715 Colloidal CdSe Quantum Dots and PQT-12-Based Low-Temperature Self-Powered Hybrid Photodetector Hemant Kumar, Student Member, IEEE, Yogesh Kumar, Student Member, IEEE, Gopal Rawat, Chandan Kumar, Bratindranath Mukherjee, Bhola N. Pal, and Satyabrata Jit, Senior Member, IEEE Abstract—In this letter, a novel dual junction self-powered hybrid photodetector is proposed using colloidal CdSe quantum dots (QDs) as an active layer (∼50-nm thickness), and PQT-12 polymer as filter layer subsequently deposited on an ITO-coated glass substrate by the spin coating method. The colloidal CdSe QDs are deposited on the PQT-12 film at 80 °C, which is much smaller than the growth temperature (usually >300 °C) of the inorganic layer of other reported hybrid self-powered detectors. The Au metal dots are deposited on the CdSe QD layer for anode electrodes while the ITO acts as the cathode electrode of the device. Two asymmetric depletion widths formed at PQT-12/CdSe and Au/CdSe junctions at two sides of the active layer controls the operation of the proposed detector. The photodetector shows band-pass response over the visible spectrum with a sharp cutoff for higher wavelengths at ∼610 nm. The maximum responsivity and detectivity of the self-powered photodetector are achieved to be ∼3.3 mA/W and 5.4 × 10 9 cmHz 1/2 W -1 , respectively, at a wavelength of ∼420 nm under the optical power density of ∼130 μW/cm 2 . The rise time and fall time of the device are found to be ∼12.01 and ∼15.32 ms, respectively. Index Terms—Colloidal CdSe quantum dots, PQT-12 conduct- ing polymer, photoresponse, response time, self-powered hybrid detector. I. I NTRODUCTION T HE hybrid photodetectors using the combination of organic and inorganic semiconductors are gaining wide attentions of the researchers to achieve high carrier mobility and high absorption coefficient of inorganic materials [1]–[7] for flexible electronics applications. Unlike the traditional photodetectors requiring an external power source for their operation, the hybrid photodetectors may be operated as a “self-powered” photodetector [1]–[3] where a self-sufficient potential is generated within the detector under illumination to govern its operation under photovoltaic short-circuit or open-circuit mode [3] without requiring any external power source. However, only a limited number of works has been reported in the literature [1]–[3]. Xie et al. [1], Game et al. [2], and Bera et al. [3] have used Spiro-MeOTAD to Manuscript received August 8, 2017; accepted August 25, 2017. Date of publication August 30, 2017; date of current version September 20, 2017. (Corresponding author: Satyabrata Jit.) H. Kumar, Y. Kumar, G. Rawat, C. Kumar, and S. Jit are with the Department of Electronics Engineering, IIT (BHU) Varanasi, Varanasi 221005, India (e-mail: hkumar.rs.ece13@iitbhu.ac.in; sjit.ece@iitbhu.ac.in). B. Mukherjee is with the Department of Metallurgical Engineering IIT (BHU) Varanasi, Varanasi 221005, India. B. N. Pal is with the School of Material Science and Technology IIT (BHU) Varanasi, Varanasi 221005, India. Color versions of one or more of the figures in this letter are available online at http://ieeexplore.ieee.org. Digital Object Identifier 10.1109/LPT.2017.2746664 prepare hybrid self-powered photodiodes with inorganic materials TiO 2 , Nitrogen-doped ZnO, and Sb 2 S 3 respec- tively. Both Game et al. [2] and Bera et al. [3] achieved wide responses covering ∼360-620 nm and ∼320-750 nm respectively whereas Xie et al. [1] achieved a spectrum selective response at ∼415 nm with a full width at half maximum (FWHM) of ∼26 nm. They [1]–[3] have used the inorganic layer annealed at a very high temperature (>300°C) as a hole blocking layer while the organic material deposited on the inorganic layer has been used as the active layer in their self-powered detectors. The major drawback of the reported self-powered hybrid detectors [1]–[3] is the inability to grow the much desired inorganic semiconductor layer to act as an active layer of an organic conducting polymer due to the high processing temperature requirement of the inorganic material at which the polymer may be melted out. Further, the fabricated inorganic semiconductor layer is used as a charge transport layer, and the organic polymer is used as an active layer [1]–[3]. Some researchers have used quantum dots (QDs) and polymer based hybrid photodetectors. Yu et al. [5] and Zhang et al. [6] have explored PbSe QDs/Perovskite [5] and PbS QDs/Poly(3-hexylthiophene) [6] hybrid heterojunc- tion based broadband phototransistors requiring suitable bias- ing voltages for their operation [5], [6]. To the best of our knowledge, no solution processed QDs based hybrid self- powered photodetector requiring low-temperature processing has been reported in the literature. In this work, we have pro- posed an Au/CdSe quantum dots (QDs)/PQT-12 polymer/ITO based self-powered hybrid photodetector where the inherently n-type low temperature (∼80°C) solution processed colloidal CdSe QDs are deposited on a PQT-12 conducting polymer coated ITO substrate by low-cost spin coating method to act as an active layer in the device. Although, the low temperature processed CdSe QDs are widely used as active layer in the conventional non-hybrid photodetectors [4], [8]–[12], the use of low-temperature processed colloidal QDs as active material in the hybrid self-powered photodetector has been proposed possibly for the first time in this letter by using PQT-12 as a filtering layer in the device. II. EXPERIMENTAL DETAILS The proposed Au/CdSe QDs/PQT-12/ITO hybrid self- powered photodetector structure is shown in Fig. 1 (a) where the light coupled into the device from the back side to achieve the maximum illumination area of 100% [13]. The front illumination is avoided since the opaque Au electrode may prevent a large portion of the incident light from entering 1041-1135 © 2017 IEEE. Personal use is permitted, but republication/redistribution requires IEEE permission. See http://www.ieee.org/publications_standards/publications/rights/index.html for more information.