Contribution of a single quantum dots layer in intermediate band solar cells: A capacitance analysis Hela Boustanji a,n , Sihem Jaziri a,b , Jean-Louis Lazzari c a Laboratoire de Physique de la Matière Condensée, Faculté des Sciences de Tunis, El Manar, 2092 Tunis, Tunisia b Laboratoire de Physique des Matériaux, Faculté des Sciences de Bizerte, 7021 Zarzouna, Tunisia c Aix-Marseille Université, CNRS, CINaM UMR 7325, Case 913, Campus de Luminy,13288 Marseille cedex 09, France article info Article history: Received 29 July 2015 Received in revised form 8 January 2016 Accepted 29 March 2016 Keywords: GaSb/GaAs type II quantum dots Schottky diode Capacitance–voltage Charge accumulation Intermediate band solar cells abstract Theoretical model and numerical analysis of charge accumulation within a single GaSb quantum dots layer embedded in GaAs-based Schottky diode is performed. We hereby give an analytical calculation of the capacitance–voltage (C–V) characteristic of GaAs-based Schottky barrier structure incorporating GaSb self-assembled quantum dots layer. The Schottky barrier is derived in different bias voltage region based on solving analytically Poisson's equation, including the effects of the dots size dispersion and the Fermi statistics of the holes in the quantum dots. The numerical simulation of capacitance–voltage curves exhibits a plateau that is caused by the high carrier concentration and the saturation of the quantum dots levels upon the applied voltage. These results are in good agreement with experiments done by Hwang et al. & 2016 Elsevier B.V. All rights reserved. 1. Introduction The Intermediate Band Solar Cells (IBSC) is a photovoltaic concept which has been proposed in order to overcome the Schockley–Queisser limit [1]. Quantum dots (QDs) IBSC attract significant interest because the quantum dot solar cells (QDSCs) have the ability to absorb incident solar energy from any direction. The efficiencies is near 10% which have been achieved with these devices [2,3]. But the efficiency of colloidal QDSCs have advanced from 1% in 2005 to 8.5% in 2013 [3].The intermediate band (IB) is the concept of putting the energy levels, approximately in the middle of a band gap in order to increase the maximum photo- current using the two-step photon absorption process. The main idea is the exploitation of zero-dimensional levels formed by QDs for the generation of additional photocurrent. The confined elec- tronic states of InAs/GaAs type I QDs were initially used to produce IB like- states located within the depletion layer of a single p–n junction [4–6]. The IB solar cell concept with type II GaSb/GaAs QDs absorber [7] located outside the p–n junction has recently attracted extensive attention for its high theoretical efficiency of 63% [8]. Several works and efforts have been published to enhance the understanding of IBSC, including the effect of coupled semi- conductor QD array on absorption coefficient [9], Auger generation [10–12] radiative and non-radiative processes in QD array [10,12], the emission and capture processes into QDs during drifting in the active region are determined by the technique deep-level transient spectroscopy (DLTS) [13], the inter-subband transition in low- dimensional semiconductors dot-in-well (DWELL)which depends on the power of two lasers [14,15]. Two approaches are involved to improve the efficiency and the performance of the solar cell. First QDs growth quality is generally optimized in terms [16] size, density, strain condition, elemental interdiffusion and density of defects. But intermediate levels introduced by type I QDs increase the radiative recombination process between electron and hole which is harmful to the solar cell efficiency. Moreover it is important for a solar cell to have high generation of free charge carriers and as low recombination mechanisms as possible. A complex interplay between charge accumulation and intrinsic traps has been early evidence by Krispin et al. by capacitance spectroscopy for InAs/GaAs QDs layer [17,18]. These recombination processes are enhanced when the absorber is placed within the built-in-field of a p–n junction. Thus charge accumulation, recombination and extraction effects within the first QDs layer in the absorbing stack are of importance to apprehend the performance of IB GaAs based solar cells, as the open circuit voltage, short current density, fill factor, and conversion efficiency all vary with the position of InAs/GaAs QD layer [19]. The collection and separation of carriers from the QDs is essential in order to enhance the efficiency. There are three important processes for extraction carriers from QD by thermal activation, tunneling carrier escape, and a two-step process of absorbing sub-gap photons of different photons energies. The Contents lists available at ScienceDirect journal homepage: www.elsevier.com/locate/solmat Solar Energy Materials & Solar Cells http://dx.doi.org/10.1016/j.solmat.2016.03.038 0927-0248/& 2016 Elsevier B.V. All rights reserved. n Corresponding author. Tel.: þ216 28286117. E-mail address: helaboustangi87@yahoo.fr (H. Boustanji). Please cite this article as: H. Boustanji, et al., Contribution of a single quantum dots layer in intermediate band solar cells: A capacitance analysis, Solar Energy Materials and Solar Cells (2016), http://dx.doi.org/10.1016/j.solmat.2016.03.038i Solar Energy Materials & Solar Cells ∎ (∎∎∎∎) ∎∎∎–∎∎∎