Abstract
Herein, we report thin films’ characterizations and photovoltaic properties of an organic semiconductor zinc phthalocyanine (ZnPc). To study the former, a 100 nm thick film of ZnPc is thermally deposited on quartz glass by using vacuum thermal evaporator at 1.5 × 10−6 mbar. Surface features of the ZnPc film are studied by using scanning electron microscope (SEM) with in situ energy dispersive x-ray spectroscopy (EDS) analysis and atomic force microscope (AFM) which reveal uniform film growth, grain sizes and shapes with slight random distribution of the grains. Ultraviolet-visible (UV-vis) and Fourier Transform Infrared (FTIR) spectroscopies are carried out of the ZnPc thin films to measure its optical bandgap (1.55 eV and 3.08 eV) as well as to study chemical composition and bond-dynamics. To explore photovoltaic properties of ZnPc, an Ag/ZnPc/PEDOT:PSS/ITO cell is fabricated by spin coating a 20 nm thick film of hole transport layer (HTL)—poly-(3,4-ethylenedioxythiophene) poly(styrene sulfonic acid) (PEDOT:PSS)—on indium tin oxide (ITO) substrate followed by thermal evaporation of a 100 nm layer of ZnPc and 50 nm silver (Ag) electrode. Current-voltage (I-V) properties of the fabricated device are measured in dark as well as under illumination at standard testing conditions (STC), i.e., 300 K, 100 mW/cm2 and 1.5 AM global by using solar simulator. The key device parameters such as ideality factor (n), barrier height ( ϕ b ), junction/interfacial resistance (Rs) and forward current rectification of the device are measured in the dark which exhibit the formation of depletion region. The Ag/ZnPc/PEDOT:PSS/ITO device demonstrates good photovoltaic characteristics by offering 0.48 fill factor (FF) and 1.28 ± 0.05% power conversion efficiency (PCE), η.
Highlights
Application of organic semiconductors in photovoltaic devices has acquired new impetus due to the growing interest in solar energy conversion
The external quantum efficiency (EQE) of the Ag/zinc phthalocyanine (ZnPc)/PEDOT:PSS/indium tin oxide (ITO) device was measured quantum efficiency (EQE) of the Ag/ZnPc/PEDOT:PSS/ITO device was measured within broad-range within broad-range from 300 to 800 nm wavelengths using an EQE system Optronic Laboratories
scanning electron microscope (SEM) micrographs of ZnPc thin film are shown in Figure 2a,b at low and high resolution, SEM micrographs of ZnPc thin film are shown in Figure 2a,b at low and high resolution, respectively
Summary
Application of organic semiconductors in photovoltaic devices has acquired new impetus due to the growing interest in solar energy conversion. The potential of zinc phthalocyanine (ZnPc) as an active material for the fabrication of organic solar cells still needs to be explored by optimizing the device structure and adding some materials as hole transport layers (HTL) to enhance its power conversion efficiency (PCE). ZnPc exhibits π-conjugated structure and acts as a hole conducting material that works as electron donor [25] It has served as a promising candidate in many electronic and optoelectronic devices [26]. ZnPc is a promising candidate for photovoltaic applications [27,28], owing to the fact that it can be synthesized, has broad absorption spectrum in the visible region and is non-toxic to the environment [29] It manifests structural self-organization characteristics, which is reflected in an efficient energy migration in the form of extinction transport [30]. The structural, morphological and optical properties of thermally evaporated ZnPc thin films are studied
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