Enhanced performance of CH3NH3PbI3−x Cl x perovskite solar cells by CH3NH3I modification of TiO2-perovskite layer interface
© The Author(s). 2016
Received: 29 March 2016
Accepted: 24 June 2016
Published: 29 June 2016
In this work, perovskite solar cells (PSCs) with CH3NH3PbI3-x Cl x as active layer and spiro-OMeTAD as hole-transport media have been fabricated by one-step method. The methylammonium iodide (CH3NH3I) solution with different concentrations is used to modify the interface between mesoporous TiO2 (meso-TiO2) film and CH3NH3PbI3−x Cl x perovskite layer. Several techniques including X-ray diffraction, scanning electron microscopy, optical absorption, electrochemical impedance spectroscopy (EIS) and photoluminescence are used to investigate the effect of the interfacial modification. It is found that the interfacial modification by CH3NH3I enhance the crystallinity and increase the grain size of CH3NH3PbI3−x Cl x layer, and improve the surface wetting properties of perovskite precursor on meso-TiO2 film. The sunlight absorption and external quantum efficiency of PSCs in the visible region with wavelength less than 600 nm have been improved. The Nyquist plots obtained from the EIS suggest that the CH3NH3I modification can reduce the charge recombination rates. The photoluminescence measurement shows that the exciton dissociation in the modified devices is more effective than that in the control samples. The photovoltaic performance of the modified devices can be significantly improved with respect to the reference (control) devices. The CH3NH3I modified devices at the optimized concentration demonstrate the average power conversion efficiency of 12.27 % in comparison with the average efficiency of 9.68 % for the reference devices.
Recently, solar cells based on composites of organometallic halide perovskite have attracted much attention due to their super high absorption coefficients, relatively high carrier mobility and easy fabrication by solution process [1–3]. The efficiency of perovskite (CH3NH3PbX3, X = Cl, Br, I)-based photovoltaic devices has greatly increased from 3.8 % to more than 20 % in just a few years [4–6]. It is well known that the microstructure and crystallinity of perovskite layer have important influence on the performance of perovskite solar cells (PSCs) . The morphology of the perovskite films influences on exciton separation, charge transfer, and recombination . The low crystallinity of the perovskite films will result in a strong leakage path and has a negative effect on the charge dynamics of PSCs [5, 9]. However, a precise control of the morphology and crystallinity of perovskite layer remains a critical challenge due to the complex crystal growth mechanism of the perovskite materials. Substantial effort has been done to improve the microstructure of PSCs by adjusting the perovskite crystallization kinetics, such as additives modification , composition optimization , solvent extraction , and controlling the temperature, annealing time, or atmosphere [13–15]. However, a control of the crystalline property and microstructure just by optimizing the fabrication processing seems to be insufficient.
It is known that surface modification has been widely used to improve the performance of organic solar cells and dye-sensitized solar cells [16–19]. Interfacial engineering has been also used as a new strategy to control the morphology of perovskite layer and improve the efficiency of PSCs. It is found that interfacial modification can significantly promote the charge transfer and reduce the recombination rate for those PSCs with metal oxides as electron transport materials [20–22]. It was reported that a modification of the interface between ZnO and perovskite layer using self-assembled monolayer can optimize the morphology of perovskite layer and improve the performance of PSCs [23, 24]. It was also demonstrated that modifying the TiO2/CH3NH3PbI3 heterojunction interface by glycine can enhance the photovoltaic performance of two-step solution-processed PSCs .
In addition, a modification of the perovskite/TiO2 interface with a nanoscale layer of Al2O3 can reduce the charge losses of the PSCs . Excess CH3NH3 + or methylammonium iodide (CH3NH3I) is very important for the improvement in the optoelectronic properties of perovskite layer. Better coverage, uniform and pinhole-free perovskite films by adding excess CH3NH3 + to the reactants of perovskite layer can be obtained . During the preparation of perovskite layer by sequential deposition method, a proper addition of CH3NH3I to PbI2 solution not only enhances the absorption but also reduces the recombination rate, resulting in the improvement of efficiency in PSCs . These results suggest that it is promise to introduce CH3NH3I to modify the interface of PSCs.
Based on these considerations, in this work, the PSCs with the glass/FTO/compact TiO2/meso-TiO2/CH3NH3PbI3−x Cl x /spiro-OMeTAD/Ag structure are fabricated by the one-step solution method. Here, we choose CH3NH3I to modify the interface between meso-TiO2 and CH3NH3PbI3−x Cl x perovskite layer and investigate the effect of CH3NH3I concentration on the microstructure of CH3NH3PbI3−x Cl x layer and photo-electronic properties of the PSCs. The related mechanism is addressed too. The results show that the CH3NH3I modification at the optimal concentration can improve the sunlight absorption and external quantum efficiency (EQE) in the visible region at the wavelengths less than 600 nm, reduce the charge recombination rate, and promote the charge transfer, resulting in the enhanced performance. The average power conversion efficiency (PCE) of the PSCs can be enhanced from 9.68 to 12.27 %, respectively.
CH3NH3I was synthesized using the reported method . For the CH3NH3I modification, the CH3NH3I of different concentration dissolved in isopropanol was spin-coated on the meso-TiO2 films at 4000 rpm. The untreated samples were chosen as the references. After the modification, these samples together with the reference samples were annealed at 60 °C for 30 min. CH3NH3I and PbCl2 (Aladdin, 99.5 %) were dissolved in N,N-dimethylformamide (Aladdin, 99.9 %) to obtain a 40 wt % precursor solution with a CH3NH3I:PbCl2 molar ratio of 3:1. The solution was filtered with a 0.45-μm pore size filters before spin-coating. To fabricate the PSCs from the above samples, a CH3NH3PbI3−x Cl x layer was deposited onto the meso-TiO2 film by spin-coating a solution of CH3NH3PbI3−x Cl x (40 wt % dissolved in DMF) at 2000 rpm for 30 s in the glove box. Then, these samples were annealed in nitrogen (N2) ambient at 100 °C for 45 min. Subsequently, 0.08 M spiro-OMeTAD in chlorobenzene solution was spin-coated onto the perovskite film. These samples were left in dry air overnight in the dark. Finally, Ag electrodes with thickness of ~100 nm were evaporated on the sample surface through a shadow mask under a vacuum of 1 × 10−4 Pa. All the as-prepared PSCs were fabricated with the standard in-plane size of 3 mm × 4 mm.
The morphology and crystallinity of the perovskite layer were investigated using scanning electron microscopy (SEM, ZEISS ULTRA 55) and the X-ray diffraction (XRD) (X’Pert PRO, Cu Ká radiation). The photovoltaic performance of these PSCs was characterized using a Keithley 2400 source meter under an illumination of 100 mW/cm2 (Newport 91160, 150 W solar simulator equipped with an AM 1.5 G filter). The radiation intensity was calibrated by a standard silicon solar cell (certified by NREL) as the reference. The EQE and the UV-vis absorption spectra were measured using a standard EQE system (Newport 66902). The electrochemical impedance spectroscopy (EIS) measurements were performed on the Zahner Zennium electrochemical workstation in the dark. A 20-mV ac-sinusoidal signal source was employed over the constant bias with the frequency ranging from 1 Hz to 4 MHz. The photoluminescence spectra (PL) were measured by a fluorescence spectrophotometer (HITACHI F-5000) exited at 405 nm. The PL spectra have been normalized to the absorbance and measured in the same conditions.
Results and Discussion
The photovoltaic parameters of the PSCs modified by CH3NH3I with different concentrations
V oc (mV)
J sc (mA/cm2)
In summary, a series of PSCs based on the structure of glass/FTO/compact TiO2/meso-TiO2/CH3NH3PbI3−x Cl x /spiro-OMeTAD/Ag have been fabricated. CH3NH3I are used to modify the interface between meso-TiO2 and CH3NH3PbI3−x Cl x . It has been revealed that modifying the interface by CH3NH3I with appropriate concentration can significantly improve the performance of PSCs. After the CH3NH3I modification, the PCE of PSCs increases to 12.27 from 9.68 % of the references device. It is suggested that the better performance for CH3NH3I modified device is mainly attributed to the improved crystalline property, increased sunlight absorption in the visible range and reduced charge recombination rate.
We acknowledge the financial support of the National Natural Science Foundation of China (Grant No. 51431006, 61271127, 51472093, 21303060,61574065), Guangdong Natural Science Foundation (2016A030313421), Guangdong Engineering Technology Center of Optofluidics Materials and Devices (2015B090903079), International Science and Technology Cooperation Platform Program of Guangzhou (No. 2014 J4500016), the State Key Program for Basic Researches of China (Grant No. 2015CB921202), the Project for Guangdong Province Universities and Colleges Pearl River Scholar Funded Scheme (2014), Science and Technology Planning Project of Guangdong Province (2015B090927006), and Program for Changjiang Scholars and Innovative Research Team in University (IRT13064).
Open AccessThis article is distributed under the terms of the Creative Commons Attribution 4.0 International License (http://creativecommons.org/licenses/by/4.0/), which permits unrestricted use, distribution, and reproduction in any medium, provided you give appropriate credit to the original author(s) and the source, provide a link to the Creative Commons license, and indicate if changes were made.
- Kojima A, Teshima K, Shirai Y, Miyasaka T (2009) Organometal halide perovskites as visible-light sensitizers for photovoltaic cells. J Am Chem Soc 131(17):6050–6051View ArticleGoogle Scholar
- Xing GC, Mathews N, Sun SY, Lim SS, Lam YM, Grätzel M, Mhaisalkar S, Sum TC (2013) Long-range balanced electron- and hole-transport lengths in organic-inorganic CH3NH3PbI3. Science 342(6156):344–347View ArticleGoogle Scholar
- Im JH, Lee CR, Lee JW, Park SW, Park NG (2011) 6.5 % efficient perovskite quantum-dot-sensitized solar cell. Nanoscale 3(10):4088–4093View ArticleGoogle Scholar
- Bi DQ, Tress W, Dar MI, Gao P, Luo JS, Renevier C, Schenk K, Abate A, Giordano F, Baena JPC, Decoppet JD, Zakeeruddin SM, Nazeeruddin MK, Grätzel M, Hagfeldt A (2016) Efficient luminescent solar cells based on tailored mixed-cation perovskites. Sci Adv 2(1):e1501170View ArticleGoogle Scholar
- Liu MZ, Johnston MB, Snaith HJ (2013) Efficient planar heterojunction perovskite solar cells by vapour deposition. Nature 501(7467):395–398View ArticleGoogle Scholar
- Yang WS, Noh JH, Jeon NJ, Kim YC, Ryu SC, Seo J, Seok SI (2015) High-performance photovoltaic perovskite layers fabricated through intramolecular exchange. Science 348(6240):1234–1237View ArticleGoogle Scholar
- Liu DY, Kelly TL (2014) Perovskite solar cells with a planar heterojunction structure prepared using room-temperature solution processing techniques. Nat Photon 8(2):133–138View ArticleGoogle Scholar
- Liang PW, Liao CY, Chueh CC, Zuo F, Williams ST, Xin XK, Lin JJ, Jen AKY (2014) Additive enhanced crystallization of solution-processed perovskite for highly efficient planar-heterojunction solar cells. Adv Mater 26(22):3748–3754View ArticleGoogle Scholar
- Eperon GE, Burlakov VM, Docampo P, Goriely A, Snaith HJ (2014) Morphological control for high performance, solution-processed planar heterojunction perovskite solar cells. Adv Funct Mater 24(1):151–157View ArticleGoogle Scholar
- Wu CG, Chiang CH, Tseng ZL, Nazeeruddin MK, Hagfeldt A, Grätzel M (2015) High efficiency stable inverted perovskite solar cells without current hysteresis. Energy Environ Sci 8(9):2725–2733View ArticleGoogle Scholar
- Yu H, Wang F, Xie FY, Li WW, Chen J, Zhao N (2014) The role of chlorine in the formation process of “CH3NH3PbI3-xClx” perovskite. Adv Funct Mater 24(45):7102–7108Google Scholar
- Jeon NJ, Noh JH, Kim YC, Yang WS, Ryu S, Seok SI (2014) Solvent engineering for high-performance inorganic-organic hybrid perovskite solar cells. Nat Mater 13(9):897–903View ArticleGoogle Scholar
- Singh T, Miyasaka T (2016) High performance perovskite solar cell via multi-cycle low temperature processing of lead acetate precursor solutions. Chem Commun 52:4784–4787View ArticleGoogle Scholar
- Troughton J, Carnie MJ, Davies ML, Charbonneau C, Jewell EH, Worsley DA, Watson TM (2016) Photonic flash-annealing of lead halide perovskite solar cells in 1 ms. J Mater Chem A 4(9):3471–3476View ArticleGoogle Scholar
- Liu TF, Jiang FY, Tong JH, Qin F, Meng W, Jiang YY, Li ZF, Zhou YH (2016) Reduction and oxidation of poly(3,4-ethylenedioxythiophene):poly(styrenesulfonate) induced by methylamine (CH3NH2)-containing atmosphere for perovskite solar cells. J Mater Chem A 4:4305–4011View ArticleGoogle Scholar
- Zhou HP, Chen Q, Li G, Luo S, Song TB, Duan HS, Hong ZR, You JB, Liu YS, Yang Y (2014) Interface engineering of highly efficient perovskite solar cells. Science 345(6196):542–546View ArticleGoogle Scholar
- Chandiran AK, Nazeeruddin MK, Grätzel M (2014) The role of insulating oxides in blocking the charge carrier recombination in dye-sensitized solar cells. Adv Funct Mater 24(11):1615–1623View ArticleGoogle Scholar
- Sun Z, Liang M, Chen J (2015) Kinetics of iodine-free redox shuttles in dye-sensitized solar cells: interfacial recombination and dye regeneration. Acc Chem Res 48(6):1541–1550View ArticleGoogle Scholar
- Azimi H, Ameri T, Zhang H, Hou Y, Quiroz COR, Min J, Hu MY, Zhang ZG, Przybilla T, Matt GJ, Spiecker E, Li YF, Brabec CJ (2015) A universal interface layer based on an amine-functionalized fullerene derivative with dual functionality for efficient solution processed organic and perovskite solar cells. Adv Energy Mater 5(8):1401692View ArticleGoogle Scholar
- Li X, Dar MI, Yi CY, Luo JS, Tschumi M, Zakeeruddin SM, Nazeeruddin MK, Han HW, Grätzel M (2015) Improved performance and stability of perovskite solar cells by crystal crosslinking with alkylphosphonic acid ω-ammonium chlorides. Nat Chem 7:703–711View ArticleGoogle Scholar
- Li WZ, Zhang W, Reenen SV, Sutton RJ, Fan JD, Haghighirad AA, Johnston MB, Wang LD, Snaith HJ (2016) Enhanced UV-light stability of planar heterojunction perovskite solar cells with caesium bromide interface modification. Energy Environ Sci 9:490–498View ArticleGoogle Scholar
- Liu LF, Mei AY, Liu TF, Jiang P, Sheng YS, Zhang LJ, Han HW (2015) Fully printable mesoscopic perovskite solar cells with organic silane self-assembled monolayer. J Am Chem Soc 137(5):1790–1793View ArticleGoogle Scholar
- Zuo LJ, Gu ZW, Ye T, Fu WF, Wu G, Li HY, Chen HZ (2015) Enhanced photovoltaic performance of CH3NH3PbI3 perovskite solar cells through interfacial engineering using self-assembling monolayer. J Am Chem Soc 137(7):2674–2679View ArticleGoogle Scholar
- Zhang SH, Zuo LJ, Chen JH, Zhang ZQ, Mai JQ, Lau TK, Lu XH, Shi MM, Chen HZ (2016) Improved photon-to-electron response of ternary blend organic solar cells with a low band gap polymer sensitizer and interfacial modification. J Mater Chem A 4:1702–1707View ArticleGoogle Scholar
- Shih YC, Wang LY, Hsieh HC, Lin KF (2015) Enhancing the photocurrent of perovskite solar cells via modification of the TiO2/CH3NH3PbI3 heterojunction interface with amino acid. J Mater Chem A 3(17):9133–9136View ArticleGoogle Scholar
- Marin-Beloqui JM, Lanzetta L, Palomares E (2015) Decreasing charge losses in perovskite solar cells through the mp-TiO2/MAPI interface engineering. Chem Mater 28(1):207–213View ArticleGoogle Scholar
- Yantara N, Yanan F, Shi C, Dewi HA, Boix PP, Mhaisalkar SG, Mathews N (2015) Unravelling the effects of Cl addition in single step CH3NH3PbI3 perovskite solar cells. Chem Mater 27(7):2309–2314View ArticleGoogle Scholar
- Xie Y, Shao F, Wang YM, Xu T, Wang DL, Huang FQ (2015) Enhanced performance of perovskite CH3NH3PbI3 solar cell by using CH3NH3I as additive in sequential deposition. ACS Appl Mater Interfaces 7(23):12937–12942View ArticleGoogle Scholar
- Conings B, Baeten L, Dobbelaere CD, Haen JD, Manca J, Boyen HG (2014) Perovskite-based hybrid solar cells exceeding 10 % efficiency with high reproducibility using a thin film sandwich approach. Adv Mater 26(13):2041–2046View ArticleGoogle Scholar
- Li WZ, Dong HP, Guo XD, Li N, Li JW, Niu GD, Wang LD (2014) Graphene oxide as dual functional interface modifier for improving wettability and retarding recombination in hybrid perovskite solar cells. J Mater Chem A 2:20105–20111View ArticleGoogle Scholar
- Yu JC, Kim DB, Baek G, Lee BR, Jung ED, Lee S, Chu JH, Lee DK, Choi KJ, Cho S, Song MH (2015) High-performance planar perovskite optoelectronic devices: a morphological and interfacial control by polar solvent treatment. Adv Mater 27(23):3492–3500View ArticleGoogle Scholar
- Zohar A, Kedem N, Levine I, Zohar D, Vilan A, Ehre D, Hodes G, Cahen D (2016) Impedance spectroscopic indication for solid state electrochemical reaction in (CH3NH3)PbI3 films. J Phys Chem Lett 7(1):191–197View ArticleGoogle Scholar
- Miyano K, Tripathi N, Yanagida M, Shirai Y (2016) Lead halide perovskite photovoltaic as a model p–i–n diode. Acc Chem Res 49(2):303–310View ArticleGoogle Scholar
- Sabba D, Agarwala S, Pramana SS, Mhaisalkar S (2014) A maskless synthesis of TiO2-nanofiber-based hierarchical structures for solid-state dye-sensitized solar cells with improved performance. Nanoscale Res Lett 9:14View ArticleGoogle Scholar
- Fabregat-Santiago F, Garcia-Belmonte G, Mora-Seró I, Bisquert J (2011) Characterization of nanostructured hybrid and organic solar cells by impedance spectroscopy. Phys Chem Chem Phys 13(20):9083–9118View ArticleGoogle Scholar
- Rau U (2007) Reciprocity relation between photovoltaic quantum efficiency and electroluminescent emission of solar cells. Phys Rev B 76(8):085303View ArticleGoogle Scholar
- Wu SJ, Li JH, Lo SC, Tai QD, Yan F (2012) Enhanced performance of hybrid solar cells based on ordered electrospun ZnO nanofibers modified with CdS on the surface. Org Electron 13(9):1569–1575View ArticleGoogle Scholar
- Gershon TS, Sigdel AK, Marin AT, van Hest MFAM, Ginley DS, Friend RH, MacManus-Driscoll JL, Berry JJ (2013) Improved fill factors in solution-processed ZnO/Cu2O photovoltaics. Thin Solid Films 536:280–285View ArticleGoogle Scholar
- Sze SM, Ng KK (2006) Physics of semiconductor devices. Wiley interscience; John Wiley & SonsGoogle Scholar
- Marco ND, Zhou HP, Chen Q, Sun PY, Liu ZH, Meng L, Yao EP, Liu YS, Schiffer A, Yang Y (2016) Guanidinium: a route to enhanced carrier lifetime and open-circuit voltage in hybrid perovskite solar cells. Nano Lett 16(2):1009–1016View ArticleGoogle Scholar
- Chen LC, Chen JC, Chen CC, Wu CG (2015) Fabrication and properties of high-efficiency perovskite/PCBM organic solar cells. Nanoscale Res Lett 10:312View ArticleGoogle Scholar
- Nejand BA, Ahmadi V, Gharibzadeh S, Shahverdi HR (2016) Cuprous oxide as a potential low-cost hole-transport material for stable perovskite solar cells. ChemSusChem 9(3):302–313View ArticleGoogle Scholar