The Effect of Multi-walled Carbon Nanotubes and Reduced Graphene Oxide Doping on the Optical and Photovoltaic Performanc
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https://doi.org/10.1007/s11664-020-08387-1 2020 The Minerals, Metals & Materials Society
The Effect of Multi-walled Carbon Nanotubes and Reduced Graphene Oxide Doping on the Optical and Photovoltaic Performance of Ag2BiI5-Based Solar Cells S.S. HOSSEINI1 and M. ADELIFARD1,2 1.—School of Physics, Damghan University, Damghan, Iran. 2.—e-mail: [email protected]
Due to the nontoxic and air-stable nature of bismuth-based photovoltaic materials, they are suitable materials to replace lead-based perovskite ones. In this research, the influence of doping with multi-walled carbon nanotubes (MWCNTs) and reduced graphene oxide (RGO) on the structural, morphological, and optical properties of silver bismuth iodide (SBI) compounds was investigated. Structural characterizations revealed the formation of the hexagonal structure in SBI thin films, and also showed improvement in the surface morphology in the MWCNT and RGO-doped thin films. All absorber layers had a relatively high absorption coefficient above 104 cm1 in the visible range, and the bandgap values varied between 1.83 eV and 2.04 eV. Also, we fabricated SBI-based solar cells, and their photovoltaic performance was studied. For the solar cell employing pure silver bismuth iodide, a photo conversion efficiency (PCE) of 0.44% was achieved. The inclusion of MWCNTs and RGO dopants in the SBI thin film PCE increased the device performance, and the highest PCE of 1.61% and 1.32% was obtained, respectively. The stability of the solar cells was also investigated under the environmental conditions. Results show that after 30 days, devices preserved about 90% of their efficiency. Key words: Lead-free, perovskite solar cells, silver bismuth iodide, MWCNT, RGO, bandgap tailoring
INTRODUCTION Lead-halide perovskites have been used as absorber layers in solar cells due to their remarkable properties such as high optical absorption coefficient, suitable bandgap, long carrier diffusion length, high carrier mobility, and low carrier recombination rates. Also, these materials can be prepared by using simple wet chemical methods at low temperatures. All these characteristics led to obtaining power conversion efficiency (PCE) greater than 25% for solar cells based on these perovskite semiconductors.1–7 However, low stability in air, lead toxicity, and also a lack of reproducibility
(Received April 22, 2020; accepted July 31, 2020)
prevent large-scale commercialization of these perovskite solar cells.8–12 Accordingly, efforts are made towards replacing lead with elements having a close valence and similar ionic radius. Some divalent cations such as Sn2+ and Ge2+ were considered for replacing Pb2+. Although the toxicity of these elements is less than lead, they are unstable in environmental conditions due to their potential oxidation from 2+ to 4+ valence.13–15 Instead, trivalent cations such as bismuth were investigated. Due to their nontoxic and air-stable properties, bismuth-based halide perovskites with the formula A3Bi2I9 (A = CH3NH3+ and Cs+), and also the isoelectronic natu
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