Efficiency Enhancement of Perovskite Solar Cells by Pumping Away the Solvent of Precursor Film Before Annealing
© Xu et al. 2016
- Received: 7 March 2016
- Accepted: 4 May 2016
- Published: 12 May 2016
A new approach to improve the quality of MAPbI3 − x Cl x perovskite film was demonstrated. It involves annealing the precursor film after pumping away the solvent, which can decrease the influence of solvent evaporation rate for the growth of the MAPbI3 − x Cl x perovskite film. The resulting film showed improved morphology, stronger absorption, fewer crystal defects, and smaller charge transfer resistance. The corresponding device demonstrated enhanced performance when compared with a reference device. The averaged value of power conversion efficiency increased from 10.61 to 12.56 %, and a champion efficiency of 14.0 % was achieved. This work paves a new way to improve the efficiency of perovskite solar cells.
- Perovskite solar cells
- Pump away the solvent
- High-quality MAPbI3 − x Cl x layer
Organo-metal halide perovskite solar cell, as a rising star in the field of thin-film photovoltaic cells, has drawn much attention, not only due to the superior optical and electrical properties of perovskite materials, such as broad light absorption range , low exciton binding energy [2, 3], longer carrier diffusion length [4–6], and higher charge carrier mobilities , but also due to its low cost and easy fabrication process. The first work employing perovskite as a light-harvesting material in solar cells was reported by Miyasaka and co-workers in 2009 with an efficiency of only 3.8 % . Almost double of this efficiency (6.5 %) was reported by Park’s research group in 2011 . Due to the dissolubility of perovskite in liquid electrolyte, devices in both works showed poor stability. When a solid-state hole conductor of 2,2′,7,7′-tetrakis(N,N-di-p-methoxyphenylamine)-9,9′-spirobifluorene (Spiro-OMeTAD) was introduced to replace the liquid electrolyte, both stability and performance were improved dramatically . Amazing progress has been made in recent times [5, 10–18] as a champion efficiency over 20 % has been reported for perovskite-based solar cell , making it an ideal candidate for next-generation photovoltaic cells. The development of perovskite solar cells came with the challenge of controlling the morphology of the perovskite layer. Such morphology is strongly influenced by several parameters such as fabrication method [5, 12, 13, 15, 20–22], additives [15, 23–26], and annealing process [16, 27–31]. Hence, efforts have been made to improve the morphology of the perovskite layer. For example, Snaith’s group introduced a dual-source thermal evaporation technique . They obtained a much compact and uniform MAPbI3 − x Cl x perovskite layer compared with the traditional one-step spin-coating method. Liang et al. added a small amount of 1,8-diiodooctane (DIO) to the MAPbI3 − x Cl x precursor solution and found that a high-quality MAPbI3 − x Cl x perovskite film was formed with improved coverage and absorption. As a result, the power conversion efficiency (PCE) was increased by 20 % . Yang Yang et al. investigated the influence of annealing conditions on the perovskite layer. They annealed the precursor film in a humid environment (~30 %) which greatly improved the film quality, grain size, carrier mobility, and lifetime. This method produced planar devices with a pretty high PCE approaching 17.1 % . Rira et al. found that a solvent evaporation rate can strongly influence the growth of the MAPbI3 − x Cl x perovskite film. By controlling the solvent evaporation rate, they obtained a MAPbI3 − x Cl x perovskite layer with improved surface coverage. Thus, improved performance was achieved .
In this letter, we report a new approach to obtain a high-quality MAPbI3 − x Cl x perovskite layer, by pumping away the solvent of precursor film before annealing to decrease the influence of solvent evaporation rate on the growth of MAPbI3 − x Cl x perovskite film. This approach was proven to be effective as a compact and uniform perovskite film with stronger absorption, fewer crystal defects, and smaller charge transfer resistance. Devices based on this high-quality perovskite film showed enhanced performance compared with the reference device. The averaged efficiency increased from 10.61 to 12.56 % and a champion PCE of 14.0 % was achieved.
Methylammonium iodide (MAI) was synthesized by reacting 10 ml of hydroiodic acid (57 wt.% in water, Alfa Aesar) with 24 ml of methylamine (33 wt.% in ethanol, Sigma-Aldrich) in ice bath under nitrogen atmosphere with constant stirring. After reacting for 2 h, the resulting white powder of MAI was collected by rotary evaporator at 50 °C. The MAI was dissolved into ethanol and evaporated for further purification. This step was repeated two times, and the MAI powder was finally collected and dried in a vacuum oven at 60 °C for 30 h. Poly(3,4-ethylenedioxythiophene):poly(p-styrene sulfonate) (PEDOT:PSS, Clevios AI 4083) and [6,6]-phenyl-C60-butyric acid methylester (PC60BM) were bought from Heraeus (Germany) and Nichem Fine Technology Co. Ltd. (Taiwan), respectively. To prepare MAPbI3 − x Cl x (30 wt.%) precursor solution, MAI and PbCl2 (Sigma-Aldrich) were dissolved into N,N-dimethylformamide (DMF) solvent with a molar ratio of 1:1 under constant stirring. The concentration of PC60BM solution was 20 mg/ml in chlorobenzene.
Measurements and Characterization
Current density-voltage (J-V) characteristics of perovskite solar cells were measured in air using a programmable Keithley 2400 source meter under AM1.5G solar irradiation at 100 mW/cm2 (Newport, Class AAA solar simulator, 94023A-U). The light intensity was calibrated by a certified Oriel Reference Cell (91150 V) and verified with an NREL-calibrated Hamamatsu S1787-04 diode. The external quantum efficiency (EQE) was measured by a certified IPCE instrument (Zolix Instruments, Inc., Solar Cell Scan 100). We utilized a field emission scanning electron microscope (FEI Quanta 200) to investigate the morphology of the perovskite layer. The absorption spectra were measured with a UV/vis spectrophotometer (PerkinElmer Lambda 750). The steady-state photoluminescence spectra were measured by utilizing Horiba Jobin-Yvon LabRAM HR800. Impedance spectroscopy (IS) measurements were performed using a Wayne Kerr 6550B precision impedance analyzer with a 50-mV perturbation oscillation signal in a frequency range from 20 Hz to 20 MHz.
Photovoltaic parameters of both the reference and modified MAPbI3 − x Cl x -based perovskite solar cells
J sc (mA/cm2)
V oc (V)
R s (Ω cm2)
R sh (Ω cm2)
We also utilized IS to investigate the series resistance (R s) of both devices. The R s consists of sheet resistance (R sheet) of the electrodes and charge transfer resistance (R CT). The following three parts contribute to the R CT: the interfaces between electrodes and charge extraction layer, the interfaces between charge extraction layer, and perovskite layer as well as the bulk of the perovskite layer . Figure 5b shows the Nyquist plots of both devices tested under applied voltage conditions approaching the V oc of perovskite solar cells. R s values of 4.9 and 2.8 kΩ were obtained for the reference and modified devices, respectively. Noticeably, the modified device showed much smaller R s. Since the main difference is located at the perovskite layer in this study, it indicates that the MAPbI3 − x Cl x perovskite layer prepared by annealing the precursor film after pumping away the solvent exhibits much smaller R CT. Enhanced performance was therefore obtained for the modified device.
A new approach which involves the annealing of a precursor film after pumping away its solvent component was introduced to obtain a high-quality MAPbI3 − x Cl x perovskite film. The device based on such high-quality film showed enhanced performance compared with the reference device. The averaged efficiency increased from 10.61 to 12.56 %, and a champion efficiency of 14.0 % was achieved. SEM, UV-vis absorption, steady-state photoluminescence spectra, and impedance spectroscopy results indicated that the improvement in device efficiency is mainly attributed to the improved morphology, stronger absorption, and fewer crystal defects as well as smaller charge transfer resistance of the modified MAPbI3 − x Cl x perovskite film. This work paves a new way to improve the efficiency of perovskite-based solar cells.
We acknowledge financial support from the Youth 973 Program (Grant No. 2015CB932700), the National Natural Science Foundation of China (Grant No. 51290273, 91433107, and 61177016), and the Natural Science Foundation of Jiangsu Province (Grant No. BK20130288). This project is also funded by the Collaborative Innovation Center of Suzhou Nano Science and Technology and by the Priority Academic Program Development of Jiangsu Higher Education Institutions (PAPD).
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 131:6050–6051View ArticleGoogle Scholar
- Miyata A, Mitioglu A, Plochocka P, Portugall O, Wang JTW, Stranks SD, Snaith HJ, Nicholas RJ (2015) Direct measurement of the exciton binding energy and effective masses for charge carriers in organic-inorganic tri-halide perovskites. Nat Phys 11:582–587View ArticleGoogle Scholar
- Lin Q, Armin A, Nagiri RCR, Burn PL, Meredith P (2015) Electro-optics of perovskite solar cells. Nat Photon 9:106–112View ArticleGoogle Scholar
- Stranks SD, Eperon GE, Grancini G, Menelaou C, Alcocer MJ, Leijtens T, Herz LM, Petrozza A, Snaith HJ (2013) Electron-hole diffusion lengths exceeding 1 micrometer in an organometal trihalide perovskite absorber. Science 342:341–344View ArticleGoogle Scholar
- Nie W, Tsai H, Asadpour R, Blancon J-C, Neukirch AJ, Gupta G, Crochet JJ, Chhowalla M, Tretiak S, Alam MA, Wang H-L, Mohite AD (2015) High-efficiency solution-processed perovskite solar cells with millimeter-scale grains. Science 347:522–525View ArticleGoogle Scholar
- Dong Q, Fang Y, Shao Y, Mulligan P, Qiu J, Cao L, Huang J (2015) Electron-hole diffusion lengths >175 m in solution-grown CH3NH3PbI3 single crystals. Science 347:967–970View ArticleGoogle Scholar
- Wehrenfennig C, Eperon GE, Johnston MB, Snaith HJ, Herz LM (2014) High charge carrier mobilities and lifetimes in organolead trihalide perovskites. Adv Mater 26:1584–1589View ArticleGoogle Scholar
- Im J-H, Lee C-R, Lee J-W, Park S-W, Park N-G (2011) 6.5% efficient perovskite quantum-dot-sensitized solar cell. Nanoscale 3:4088–4093View ArticleGoogle Scholar
- Kim H-S, Lee C-R, Im J-H, Lee K-B, Moehl T, Marchioro A, Moon S-J, Humphry-Baker R, Yum J-H, Moser JE, Gratzel M, Park N-G (2012) Lead iodide perovskite sensitized all-solid-state submicron thin film mesoscopic solar cell with efficiency exceeding 9 %. Sci Rep 2:591Google Scholar
- Lee MM, Teuscher J, Miyasaka T, Murakami TN, Snaith HJ (2012) Efficient hybrid solar cells based on meso-superstructured organometal halide perovskites. Science 338:643–647View ArticleGoogle Scholar
- Ball JM, Lee MM, Hey A, Snaith HJ (2013) Low-temperature processed meso-superstructured to thin-film perovskite solar cells. Energy Environ Sci 6:1739–1743View ArticleGoogle Scholar
- Burschka J, Pellet N, Moon S-J, Humphry-Baker R, Gao P, Nazeeruddin MK, Grätzel M (2013) Sequential deposition as a route to high-performance perovskite-sensitized solar cells. Nature 499:316–319View ArticleGoogle Scholar
- Liu M, Johnston MB, Snaith HJ (2013) Efficient planar heterojunction perovskite solar cells by vapour deposition. Nature 501:395–398View ArticleGoogle Scholar
- Liu D, Kelly TL (2014) Perovskite solar cells with a planar heterojunction structure prepared using room-temperature solution processing techniques. Nature Photon 8:133–138View ArticleGoogle Scholar
- Jeon NJ, Noh JH, Kim YC, Yang WS, Ryu S, II Seok S (2014) Solvent engineering for high-performance inorganic-organic hybrid perovskite solar cells. Nature Mater 13:897–903View ArticleGoogle Scholar
- You J, Yang Y, Hong Z, Song T-B, Meng L, Liu Y, Jiang C, Zhou H, Chang W-H, Li G, Yang Y (2014) Moisture assisted perovskite film growth for high performance solar cells. Appl Phys Lett 105:183902View ArticleGoogle Scholar
- Zhou H, Chen Q, Li G, Luo S, Song T, Duan H-S, Hong Z, You J, Liu Y, Yang Y (2014) Interface engineering of highly efficient perovskite solar cells. Science 345:542–546View ArticleGoogle Scholar
- Ahn N, Son D-Y, Jang I-H, Kang SM, Choi M, Park N-G (2015) Highly reproducible perovskite solar cells with average efficiency of 18.3 % and best efficiency of 19.7 % fabricated via Lewis base adduct of lead(II) iodide. J Am Chem Soc 137:8696–8699View ArticleGoogle Scholar
- Yang WS, Noh JH, Jeon NJ, Kim YC, Ryu S, Seo J, II Seok S (2015) High-performance photovoltaic perovskite layers fabricated through intramolecular exchange. Science 348:6240Google Scholar
- Chen Q, Zhou H, Hong Z, Luo S, Duan H-S, Wang H-H, Liu Y, Li G, Yang Y (2014) Planar heterojunction perovskite solar cells via vapor-assisted solution process. J Am Chem Soc 136:622–625View ArticleGoogle Scholar
- Xiao M, Huang F, Huang W, Dkhissi Y, Zhu Y, Etheridge J, Gray-Weale A, Bach U, Cheng Y-B, Spiccia L (2014) A fast deposition-crystallization procedure for highly efficient lead iodide perovskite thin-film solar cells. Angew Chem Int Ed 126:10056–10061View ArticleGoogle Scholar
- Xiao Z, Bi C, Shao Y, Dong Q, Wang Q, Yuan Y, Wang C, Gao Y, Huang J (2014) Efficient, high yield perovskite photovoltaic devices grown by interdiffusion of solution-processed precursor stacking layers. Energy Environ Sci 7:2619–2623View ArticleGoogle Scholar
- Liang P-W, Liao C-Y, Chueh C-C, Zuo F, Williams ST, Xin X-K, Lin J, Jen Alex K-Y (2014) Additive enhanced crystallization of solution-processed perovskite for highly efficient planar-heterojunction solar cells. Adv Mater 26:3748–3754View ArticleGoogle Scholar
- Song X, Wang W, Sun P, Ma W, Chen Z-K (2015) Additive to regulate the perovskite crystal film growth in planar heterojunction solar cells. Appl Phys Lett 106:864Google Scholar
- Zhao Y, Zhu K (2014) CH3NH3Cl-assisted one-step solution growth of CH3NH3PbI3: structure, charge-carrier dynamics, and photovoltaic properties of perovskite solar cells. J Phys Chem C 118:9412–9418View ArticleGoogle Scholar
- Jeon Y-J, Lee S, Kang R, Kim J-E, Yeo J-S, Lee S-H, Kim S-S, Yun J-M, Kim D-Y (2014) Planar heterojunction perovskite solar cells with superior reproducibility. Sci Rep 4:6953View 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 24:151–157View ArticleGoogle Scholar
- Kang R, Kim J-E, Yeo J-S, Lee S, Jeon Y-J, Kim D-Y (2014) Optimized organometal halide perovskite planar hybrid solar cells via control of solvent evaporation rate. J Phys Chem C 118:26513–26520View ArticleGoogle Scholar
- Xiao Z, Dong Q, Bi C, Shao Y, Yuan Y, Huang J (2014) Solvent annealing of perovskite-induced crystal growth for photovoltaic-device efficiency enhancement. Adv Mater 26:6503–6509View ArticleGoogle Scholar
- Ren Z, Ng A, Shen Q, Gokkaya HC, Wang J, Yang L, Yiu W-K, Bai G, Djurišić AB, Leung WW, Hao J, Chan WK, Surya C (2014) Thermal assisted oxygen annealing for high efficiency planar CH3NH3PbI3 perovskite solar cells. Sci Rep 4:6752View ArticleGoogle Scholar
- Li Y, Cooper JK, Buonsanti R, Giannini C, Liu Y, Toma FM, Sharp ID (2015) Fabrication of planar heterojunction perovskite solar cells by controlled low-pressure vapor annealing. J Phys Chem Lett 6:493–499View ArticleGoogle Scholar
- Chen Q, Nicholas DM, Yang Y(M), Song T-B, Chen C-C, Zhao H, Hong Z, Zhou H, Yang Y (2015) Under the spotlight: the organic–inorganic hybrid halide perovskite for optoelectronic applications. Nano Today 10:355–396View ArticleGoogle Scholar
- Kim J-S, Chung W-S, Kim K, Kim DY, Paeng K-J, Jo SM, Jang S-Y (2010) Performance optimization of polymer solar cells using electrostatically sprayed photoactive layers. Adv Funct Mater 20:3538–3546View ArticleGoogle Scholar