Nano metal-enhanced power conversion efficiency in CH3NH3PbI3 solar cells
Introduction
In the last few years, organometal halide perovskite has been regarded as the most promising material in photovoltaic field due to its high optical absorption coefficient [1], long electron-hole diffusion length [2], excellent carrier mobility and low nonradiative auger recombination, etc [3]. Initially, the developments of perovskite solar cells (PSCs) are not very fast: the power conversion efficiency (PCE) of them increases only from 3.8% to 6.5% between 2009 and 2012, which is mainly due to the liquid-state electrolyte used in these cells [4], [5]. But, after the all-solid-state PSC being reported by Park's group in 2012 [6], who firstly introduced ‘spiroOMeTAD’ as the hole transporting layer in PSCs, and till 2015 the PCEs have increased rapidly from 9.0% to 20.1% in just four years [1], [2], [3], [7], [8], [9], [10]. However, in the past year, this development comes to a standstill again (from 20.1% to 21.0%) [11]. For further improving the PCE of PSCs, a promising way is taking use of the localized surface plasmonic (LSP) effect by metal nanoparticles (NPs). In fact, LSP-enhanced PSCs have been in scientists’ views since year 2013: Au@SiO2 NPs were firstly used by Snaith's group in mesosuperstructured PSCs, and a PCE increase from 10.7 to 11.4% was obtained [12]; Jeng's group brought Ag nanoplates into the hole transport layer (HTL) to accelerate the carriers’ transport with the PCE increasing by up to 13% [13]; Park et al. embedded Au NPs into the HTL as well, and finally improved the PCE from 12.66% to 12.74% [14]. Although other similar researches were reported, the basic principle used in these studies is the same which is the near-field enhancement effect excited by LSP resonance of metal NPs. In fact, except for near-field enhancement effect, the far-field scattering (forward scattering) effect of LSP is also very important in LSP-enhanced solar cells. Incident lights will scatter preferentially into the larger-permittivity dielectric when metal NPs are put on the interface between two dielectrics, resulting in an angular spread which can induce an increase of optical path length and at last enhance the absorption of the dielectric. Based on this principle, enhanced solar cells by far-field scattering effect of metal NPs have been widely researched in the last decade [15], [16], including thin a-Si solar cell [17], organic thin film solar cell [18], polymer solar cells [19] and commercial pc-Si solar cell [20], etc. However, due to the brief history of PSCs, the researches for far-field scattering effect in enhancing PSCs have always been ignored until now. Therefore, for filling this gap and searching a new way to further improve the performances of PSCs as well, we investigated the far-field scattering effect in enhancing the performance of CH3NH3PbI3 solar cell with two structures by using the finite difference time domain (FDTD) method for the first time in this paper.
Section snippets
Theoretical details
To research the performances of a solar cell, the most straightforward way is to obtain its current density-voltage (J-V) characterization, from which all the details like PCE, short circuit current density (Jsc), open circuit voltage (Voc) and fill factor (FF) can be achieved. Combining with the detailed balance model and black-body radiation law, Choy provided a way to estimate the J-V characterization of PSCs [21], and in our paper parts of this method are adopted. Commonly, the J-V
Results and discussion
To better demonstrate the feasibility for using far-field scattering effect in improving PCE of PSCs, we firstly design a simplest structure with corresponding schematic is shown as the inset in Fig. 3. In this structure, periodic Ag nanospheres (100 nm) with SC of 10% are putted on 275 nm thick CH3NH3PbI3 thin film which is deposited on a 50 nm thick Ag back electrode (labeled by APA_100_10). As a control, structure with no Ag NPs (labeled by PA_0) is also calculated. Fig. 2(a) shows the
Conclusions
In conclusion, two structures are designed in this paper to explore the feasibility for using far-field scattering effect by metal NPs in improving the PCE of PSCs. Inspiringly, both of them exhibit the exciting results, bringing the max PCE enhancements by 12.18% and 8.03% respectively. Especially, considering the huge handleability of the IALTPA structure, our researches undoubtedly provide a valuable method for further improving the performance of other PSCs.
Prime novelty statement
For the first time, far-field scattering effect of localized surface plasmon excited by metal nanoparticles (NPs) has been introduced in improving the performances of organometal halide perovskite solar cells (PSCs) in this paper. The main innovation of this study is that we provide a new method for further enhancing the power conversion efficiency (PCE) of the PSCs, which has come to a standstill (20.1%) since the past year. Two structures are designed to demonstrate this feasibility by
Acknowledgements
At last, we sincerely thank the National Natural Science Foundation of China (No. 11474187), Shandong Provincial Natural Science Foundation (No. ZR2014BP003) and China Postdoctoral Science Foundation (No. 2016M600550 and No. 2016M602716) for financial support.
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