Simulation of Copper Phthalocyanine (CuPc)/Fullerene (C60) Heterojunction. photovoltaic cell with and without electron t
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Simulation of Copper Phthalocyanine/Fullerene Heterojunction Photovoltaic Cell With and Without Electron Transport Layer (ETL) Nikhil T. Satyala1, Wudyalew T. Wondmagegn1, Ron J. Pieper1 and Michael R. Korn1 1. University of Texas at Tyler, Electrical Engineering, Tyler, TX 75799, U.S.A. ABSTRACT A two-dimensional finite element simulation model for the bi-layer heterostructure organic photovoltaic (PV) cell, based on copper phthalocyanine (CuPc) and fullerene (C60) in the presence and absence of electron transport layers (ETLs) is presented. The effect of bathocuproine (BCP), tris(8-hydroxyquinolinato)aluminum (Alq3), and copper phthalocyanine (CuPc) as ETLs on short-circuit current (Jsc), open-circuit voltage (Voc), and power conversion efficiency (PCE) is investigated. The Frenkel-Poole mobility model was employed in describing the conduction mechanisms in the active layers. Singlet exciton and Langevin recombination techniques were employed to describe excitonic generation and recombination, respectively. The obtained simulation results demonstrate that the efficiency of PV cells is primarily dependent on the short-circuit current, the absorption capability of the active layers, and the charge collection efficiency at the electrodes. In addition, significant reduction in power conversion efficiency is observed with increasing thickness of the ETL layer. From among the modeled device designs, PV cells containing a 50Å BCP layer result in the best power conversion efficiencies of 2.05%. INTRODUCTION Various designs for organic photovoltaic (PV) cells have been reported in the literature [1]. The heterojunction (HJ) solar cell was introduced by Tang in the mid 80s, which employs a combination of an organic donor and of an organic acceptor material as the photoactive layers [2]. Excitons generated in these layers by photon absorption dissociate at the donor/acceptor interface. To prevent the diffusion of generated excitons to the cathode and to reduce the subsequent exciton quenching at the acceptor/cathode interface, Peumans and Forrest introduced bathocuproine (BCP) as an electron transport layer ETL to a Copper phthalocyanine (CuPc)/Fullerene (C60) PV cell rendering the device a double HJ cell [3]. Addition of this ETL resulted in an increase in power conversion efficiencies to nearly 3.6% and 4.2% [3,4]. It was also noted that the thickness of the ETL in double HJ cells significantly affected Jsc and PCE [3, 5]. Other materials employed as ETLs include bathophenanthroline (BPhen), 1,3,5-tris (Nphenylbenz-imidazol-2-yl)benzene (TPBi), tris(8-hydroxyquinolinato)aluminum (Alq3), and CuPc [6]. Whereas BPhen, BCP and Alq3 were well known for their electron transport capabilities, CuPc was widely used as a hole injection layer in OLEDs. However, CuPc’s high level of electrical and chemical stability makes it a suitable ETL material [7, 8]. Based on this concept, a variety of PV cells comprising ETLs have been fabricated, tested, and reported in the literature [6,8]. However, simulation studies of such cel
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