A Strategy to Achieve High-Efﬁciency Organolead Trihalide Perovskite Solar Cells SHABNAM ANDALIBI, 1,4 ALI ROSTAMI, 2,5 GAFAR DARVISH, 1 and MOHAMMAD KAZEM MORAVVEJ-FARSHI 3 1.—Department of Electrical Engineering, Science and Research Branch, Islamic Azad University, Tehran, Iran. 2.—Photonics and Nanocrystal Research Lab. (PNRL), Faculty of Electrical and Computer Engineering, University of Tabriz, Tabriz 5166614761, Iran. 3.—Advanced Devices Simulation Lab, Faculty of Electrical and Computer Engineering, Tarbiat Modares University, Tehran 1411713116, Iran. 4.—e-mail: sh.andalibi@srbiau.ac.ir. 5.—e-mail: rostami@tabrizu.ac.ir Recent theoretical and experimental reports have shown that organometal lead halide perovskite solar cells have attracted attention as a low-cost pho- tovoltaic technology offering high power conversion efﬁciency. However, the photovoltaic efﬁciency of these materials is still limited by poor chemical and structural stability in the case of methylammonium lead triiodide and by large bandgap in the case of methylammonium lead tribromide or trichloride. To obtain high-performance devices, we have investigated the computationally optimal efﬁciency for these materials using the detailed-balance method and present optimal intermediate-band perovskite solar cells with high open-cir- cuit voltage. We model different halide perovskites using density function theory calculations and study their bandgap and absorption coefﬁcient. Based on calculation results, surprisingly Hg doping in different halide perovskites introduces a narrow partially ﬁlled intermediate band in the forbidden bandgap. We investigate electrical and optical properties of MAPb 0.97 Hg 0.03 I 3 , MAPb 0.96 Hg 0.04 Br 3 , and MAPb 0.96 Hg 0.04 Cl 3 and calculate the high absorption efﬁciency of the different perovskite structures to create thin ﬁlms suitable for photovoltaic devices. Key words: Solar cells, perovskite photovoltaic, organolead halide, intermediate-band solar cells INTRODUCTION Over the last few decades, global energy consump- tion has increased along with population growth. About 16% of global ﬁnal energy consumption presently comes from renewable resources. Among renewable energy conversion devices, solar cells based on the photovoltaic effect make an important contribution in terms of low-cost, clean energy. According to National Renewable Energy Laboratory (NREL) reports, organometal lead halide solar cells have achieved great progress in terms of power conversion efﬁciency (PCE) over the past few years. 1–4 Organometal trihalide perovskites with methylammonium lead trihalide [MAPbX 3 (X =I  , Br  , Cl  )] structure are used as the light-harvesting layer in this kind of solar cell. 5–7 These hybrid perovskites are important for solar cell technology because they have simple, low-cost solution-processing synthesis methods, direct band- gap, large absorption coefﬁcient, high carrier mobil- ity, and long carrier diffusion length. 8 Even though organometal perovskite materials contain heavy metals (Pb and Hg), which are harmful to the environment and poisonous, their amount in a thin- ﬁlm cell is minimal. Recent theoretical and experi- mental studies have commonly focused on iodide halide perovskite (MAPbI 3 ) because of its good carrier properties, optimal bandgap (1.5 eV), and compati- bility with solution-based processing. 9–14 However, bromide and chloride halide perovskites (MAPbBr 3 (Received March 2, 2016; accepted June 23, 2016) Journal of ELECTRONIC MATERIALS DOI: 10.1007/s11664-016-4772-2 Ó 2016 The Minerals, Metals & Materials Society