332 The 2 nd Asian Symposium on Electromagnetics and Photonics Engineering August 28-30, 2013, Tabriz, Iran ASEPE 2013-Poster, PFr4 Analysis of metallic intermediate band formation in silicon based high efficiency solar cell materials H. Heidarzadeh 1* , A. Rostami 1, 2 , M. Dolatyari 2 , H. Baghban 2 , and G. Rostami 2 1 Photonics and Nanocrystal Research Lab. (PNRL), Department of Electrical and Computer Engineering, University of Tabriz, Tabriz, Iran 2 School of Engineering-Emerging Technologies, University of Tabriz, Tabriz, Iran *1 h_heidarzadeh89@ms.tabrizu.ac.ir Abstract-One possible way for enhancing the efficiency of photovoltaic (PV) cells is the use of materials with more than one band gap. In the intermediate band gap solar cell (IBSC) an intermediate narrow metallic band (IB) is placed in the traditional forbidden band gap which can extend absorption region. This generates extra electron–hole pairs and thus increases the current without decreasing the output voltage and therefore increases the quantum efficiency. Substitution of transition metal atoms (TM) in the 3C-SiC may give rise to a type of high-efficiency photovoltaic materials with intermediate bands to absorb low energy photons. In the present study comprehensive analysis is carried out on this kind of materials. Theoretical studies confirm the formation of suitable mini- bands within 3C-SiC band gap by doping of transition metals in 3C-SiC crystal structure. The mini bands mainly are created by 3d orbitals of the transition metals. Absorption coefficient, density of states and band structure are three important features of the proposed materials. Here, we calculated these characteristics for the 3C-SiC doped with TM=Fe as candidates for presenting an isolated partially-filled narrow bands between the valance band and the conduction band of 3C-SiC. The results show that a Fe 3+ doped3C-SiC is a good candidate for high efficiency solar cell. Keywords- Intermediate band solar cell; transition metal; silicon; 3C-SiC I. INTRODUCTION Exploitation of new energy sources has gained considerable attention due to the world-wide energy shortage and environment pollution. It is possible to enhance solar cell efficiency by taking advantage of sub-gap absorption to increase the current density due to improvement the wavelength response [1-3]. The intermediate concept in the field of semiconductor solar cells is based on having a narrow band inside the main band gap, which allows the absorption of extra low energy photons that promotes a second electron-hole pair, and hence, increasing the solar cell photocurrent without affecting the cell voltage. The intermediate band (IB) solar cells present efficiencies higher than those established by the Shockley-Queisser limit [1, 4]. IB solar cells can deliver a high photo voltage by absorbing two sub band gap photons to produce one high energy electron. As a result, the photocurrent of the solar cell can be increased without decreasing the voltage. Crystalline silicon in multi-crystalline and mono-crystalline forms is an important material for solar cell technology. Since the silicon technology is getting cheaper and its dominance seems to be unshakable, 3C-SiC as a member of this family has attracted great interest in recent years due to excellent electronic prosperities such as high electron mobility [5, 6]. Silicon single junction solar cells have high short circuit current (up to 40 mA/cm 2 ) beside relatively low open circuit voltage (lower than 0.7V) [7, 8]. On the contrary, 3C-SiC has higher band gap (E g =2.2eV) and presents higher open circuit voltage while it suffers lower short circuit current compared with silicon. Optimal IBSC has a total band gap of about 1.95eV. Practically, 3C- SiC has the closest band gap to the optimal value (band gap of 2.2eV) and also, meets the economic requirements for mass production due to mature silicon technology. Considering the aforementioned background about IBSCs and the interests in next generation of high-efficiency Si-based solar cells, the necessity of a comprehensive survey about Si-based IBSCs is felt due to lack of theoretic and experimental study in this case. Beside these facts, large band gap of 3C-SiC and the possibility to design an intermediate band close to the optimal theoretical value intensifies our research interests. In current study we propose Fe 3+ ion implantation in 3C-SiC at appropriate concentrations for IB formation to introduce a realistic candidate for a Si-based IBSC. For this purpose, Fe 3+ as a cation of transition elements, are introduced into the crystal structure of host semiconductor (3C-SiC), instead of some Si atoms in such a way that 3d orbitals of Fe 3+ can form the IB levels. A schematic band diagram of an IBSC is shown in fig.1. Beside the main band gap, two other sub bands are created in intrinsic region. High energy (E ≥ E g ) photons can promote electrons from the VB to the CB and low energy photons create additional electron-hole pairs in two steps; some photons promote electrons from VB to IB and others promote from IB to CB which, could improve the short circuit current. Since, open circuit voltage depends on the gap between the VB and CB, output voltage of solar cell will not decrease.