Enhancement of Perovskite Solar Cells Efficiency using N-Doped TiO2 Nanorod Arrays as Electron Transfer Layer
Zhang et al. Nanoscale Research Letters
Enhancement of Perovskite Solar Cells Efficiency using N-Doped TiO Nanorod 2 Arrays as Electron Transfer Layer
Zhen-Long Zhang 1
Jun-Feng Li 1
Xiao-Li Wang 1
Jian-Qiang Qin 1
Wen-Jia Shi 1
Yue-Feng Liu 1
Hui-Ping Gao 1
Yan-Li Mao 0 1
0 Institute for Computational Materials Science, Henan University , Kaifeng 475004 , China
1 School of Physics and Electronics, Henan University , Kaifeng 475004 , China
In this paper, N-doped TiO2 (N-TiO2) nanorod arrays were synthesized with hydrothermal method, and perovskite solar cells were fabricated using them as electron transfer layer. The solar cell performance was optimized by changing the N doping contents. The power conversion efficiency of solar cells based on N-TiO2 with the N doping content of 1% (N/Ti, atomic ratio) has been achieved 11.1%, which was 14.7% higher than that of solar cells based on un-doped TiO2. To get an insight into the improvement, some investigations were performed. The structure was examined with X-ray powder diffraction (XRD), and morphology was examined by scanning electron microscopy (SEM). Energy dispersive spectrometer (EDS) and Tauc plot spectra indicated the incorporation of N in TiO2 nanorods. Absorption spectra showed higher absorption of visible light for N-TiO2 than un-doped TiO2. The N doping reduced the energy band gap from 3.03 to 2.74 eV. The photoluminescence (PL) and time-resolved photoluminescence (TRPL) spectra displayed the faster electron transfer from perovskite layer to N-TiO2 than to un-doped TiO2. Electrochemical impedance spectroscopy (EIS) showed the smaller resistance of device based on N-TiO2 than that on un-doped TiO2.
Enhancement of efficiency; N-doped TiO2 nanorod arrays; Electron transfer layer
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Background
In recent years, extensive studies are focused on
perovskite solar cells (PSCs) due to their outstanding
properties, such as large absorption coefficient, electron-hole
diffusion length, and high charge carrier mobility [1–5].
The power conversion efficiency (PCE) of perovskite
solar cells has been over 22% [6]. Conventionally,
perovskite solar cells consist of a perovskite layer
sandwiched between an electron transfer material (ETM)
layer and a hole transfer material (HTM) layer.
Mesoporous TiO2 has been used as the ETM in most of the
perovskite solar cells [7, 8]. Compared with the mesoporous
structure, one dimensional (1D) nanostructure has some
advantages, such as easy pore filling of active layer or
HTM, better electron transfer, and lower charge
recombination [9, 10]. Therefore, TiO2 nanorods (NRs) have
been widely applied to perovskite solar cells [11, 12].
However, there are a mass of oxygen vacancies defects
exist in pristine TiO2 nanorods, which reduces the
efficiency and stability of the perovskite solar cell [13].
In order to solve the issues, some methods have been
adopted, such as metal doping [14, 15] and nonmetal
doping [16]. It has been reported that N-doped TiO2 as
a photoanode of dye-sensitized solar cells (DSSCs) can
improve the energy conversion efficiency due to the
change of properties of TiO2, such as electron lifetime
prolongation, charge transfer resistance reduction, and
visible light absorption extension [17, 18].
We wondered about the effect of N-doped TiO2 on
the performance of perovskite solar cells. Hence, in
the present study, we synthesized N-doped TiO2
(NTiO2) nanorod arrays with hydrothermal method and
fabricated perovskite solar cells using them as
electron transfer layer. The solar cell performance was
optimized by changing the N doping contents. The
PCE of solar cells based on N-TiO2 with the N
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doping content of 1% (N/Ti, atomic ratio) has been
achieved 11.1%, which was 14.7% higher than that of
solar cells based on un-doped TiO2. The possible
mechanisms of enhancement were discussed based on
some investigations.
Methods
Growth of TiO2 Nanorod Arrays
Patterned fluorine-doped tin oxide (FTO)-coated glass
substrate was cleaned by sonication for 20 min in
detergent, acetone, 2-propanol, and ethanol, respectively. A
TiO2 compact layer was deposited by dipping the
substrate in a 0.2 M TiCl4 aqueous solution at 70 °C for
30 min. TiO2 NRs were grown on the treated FTO
substrate by a hydrothermal method in our previous report
[19]. A 0.7 mL of titanium(IV) n-butoxide was added to
a mixture of hydrochloric acid and deionized water.
Subsequently, the pre-calculated amount of CO(NH2)2 was
added to the solution (the nominal N/Ti atomic ratio,
0.5, 1, 2, and 3%) and stirred until it was completely
dissolved. T (...truncated)