Efficient Perovskite-organic Bulk Heterojunction Hybrid Integrated Solar Cells

TANG Tong,ZUO Hong-wen,WANG Ya-ling,QINWen-jing, CAO Huan-qi,YANG Li-ying*,YAO Cong,GE Zi-yi,YIN Shou-gen*

(1.Key Laboratory ofDisplay Materials and Photoelectric Devices,Education Ministry ofChina, School ofMaterials Science and Engineering,Tianjin University of Technology,Tianjin 300384,China; 2.Tianjin Key Laboratory for Photoelectric Materials and Devices,Tianjin University ofTechnology,Tianjin 300384,China; 3.China Electronics Technology Group Corporation No.18th Research Institute,Tianjin 300384,China; 4.Ningbo Institute ofMaterials Technology&Engineering,Chinese Academy of Sciences,Ningbo 315201,China) *Corresponding Author,E-mail:liyingyang@tjut.edu.cn

Efficient Perovskite-organic Bulk Heterojunction Hybrid Integrated Solar Cells

TANG Tong1,2,ZUO Hong-wen1,2,WANG Ya-ling1,2,QINWen-jing1,2, CAO Huan-qi1,2,YANG Li-ying1,2*,YAO Cong3*,GE Zi-yi4*,YIN Shou-gen1,2*

(1.Key Laboratory ofDisplay Materials and Photoelectric Devices,Education Ministry ofChina, School ofMaterials Science and Engineering,Tianjin University of Technology,Tianjin 300384,China; 2.Tianjin Key Laboratory for Photoelectric Materials and Devices,Tianjin University ofTechnology,Tianjin 300384,China; 3.China Electronics Technology Group Corporation No.18th Research Institute,Tianjin 300384,China; 4.Ningbo Institute ofMaterials Technology&Engineering,Chinese Academy of Sciences,Ningbo 315201,China) *Corresponding Author,E-mail:liyingyang@tjut.edu.cn

An integrated perovskite/organic bulk-heterojunction(BHJ)photovoltaic device was fabricated for efficient lightharvesting and energy conversion.The structure of the solar cells consists of two photovoltaic layers,namely a methylammonium lead iodide(CH3NH3PbI3)and poly(3-hexylthiophene)(P3HT)blended with methanofullerene[6,6]-phenyl C61-butyric acid methyl ester(PCBM)organic BHJactive layer.The power conversion efficiency(PCE)of6.54%was achieved in the integrated devicewith a Jscof19.14 mA/cm2,a Vocof0.76 V,and a FF of 45.0%.Compared to that of CH3NH3PbI3/PCBM planar device,the enhanced performance indicates that the BHJ film absorbs light and contributes to the current density of the device.Our research further demonstrates the compatibility and synergistic potential of the perovskite and organic bulk-heterojunction(BHJ)photovoltaic device.

perovskite;bulk heterojunction;integrated solar cells

1 Introduction

The ever increasing world energy consumption entails the depletion of fossil energy resources.Consequently,people are facing a growing quest for the development of low-cost renewable energy sources. Solar technology is regarded as the one of the most prominent choice to directly convert renewable energy into electricity using photovoltaic cells.Conventional silicon-based solar cells which permit an efficient conversion of solar energy into electrical power have developed and commercialized many years ago. However,the high purity requirements for the raw materialsmake the fabrication processes and the resulting energy payback time too long and too cost-intensive to impair the deployment of such solar cells on a terawatt scale.During the past three decades, several promising alternatives based on cost-effective materials have been proposed[1-3].Amongst them, organic-inorganic hybrid metal halide perovskites, CH3NH3MX3(M=Pb,Sn;X=halogen),have gained notable attention and shown high performance due to direct band gap,large absorption coefficient, long exciton diffusion lengths and high charge carrier mobility[4-9].The potential advantage of the metal halide perovskite photovoltaic technologies is their use of abundant low-costmaterials that can be processed from solution,enabling the application of large-area printing techniques to reduce the fabrication costs and the energy payback time[10-11].Since the pioneer work by Miyasaka and co-workers in 2009,various device structures ranging from mesoscopic structure to the planar heterojunction architecture have been explored[12-16].To date,through optimizing device design,material interfaces and processing techniques,a certified efficiency of 20.1% has been reported.These recent developments demonstrate the enormous potential of perovskite solar cells,with trajectory suggesting that they should soon compete with traditional silicon solar cells.

In this paper,we demonstrate the fabrication of aperovskite-organic bulk heterojunction hybrid integrated solar cells consisting of two photovoltaic layers, namely amethylammonium lead iodide(CH3NH3PbI3) and poly(3-hexylthiophene)(P3HT)blended with methanofullerene[6,6]-phenyl C61-butyric acid methyl ester(PCBM)organic BHJ active layer. UV-Vis and atomic forcemicroscopy(AFM)measurementswere used to characterize the interface between the perovskite and the organic bulk heterojunction.

2 Experiments

2.1 M aterials

Poly(3-hexylthiophene)(P3HT,4002-E)with purity over 99%was purchased from Rieke Met.Inc. Fullerene derivative(PCBM)with purity over 99% was obtained from Solenne B.V.,Netherlands. PbI2(99.999%)was purchased from Aldrich Co.. An aqueous dispersion of PEDOT:PSS(Baytron?P VP Al 4083)was obtained from Heraeus Co..All the materials were used as received.CH3NH3Iwas synthesized using the same method as published in literature[17].ITO-coated glass with a sheet resistance of 10Ω/□was used for device fabrication. The routine cleaning procedure includes ultra-sonication in a solution of detergent,deionized water, and isopropyl alcohol in sequence.

2.2 Device Fabrication and Performance M easurements

The schematic device structures and the energy level diagrams of each layer are shown in Fig.1. The procedure for the solar cell device fabrication is described as follows.PEDOT:PSS layer of about 40 nm was obtained by spin coating at 3 000 r/min for 30 s on ITO coated glass substrates,followed by baking at 120℃for 30 min in air.For depositing the perovskite layer,first a layer of PbI2was spincoated on top of the PEDOT:PSS-coated ITO substrate from a 1 mol/L DMF solution.After the PbI2film was dried at 70℃in air,CH3NH3Iwas spincoated on top of PbI2layer from an isopropanol solution with a concentration of 38 mg/mL with a spin rate of 1 500 r/min to form the perovskite structure and then annealed at 90℃for 2 h.The blend of P3HT:PCBM(1:0.8 by weight)chlorobenzene solution is spin-coated at 800 r/min for 10 s on the perovskite layer to form a 100 nm thick active layer. Finally,100 nm Al are thermally evaporated under a vacuum of a pressure of 1×10-4Pa.For comparison,80 nm PCBM(20 mg/mL in o-dichlorobenzene)was then sequentially deposited by spin coating at1 500 r/min for12 s on top of CH3NH3PbI3layer to form control perovskite planar device structure.All the fabrication and characterization procedures were performed in an ambient atmosphere at room temperature.The active layer area of the device is 0.09 cm2defined by a shadow mask.

J-V characteristics of the un-encapsulated devicesweremeasured under intensity of100 mW/cm2illuminations by using a 300 W solar simulator with an AM 1.5 G filter.The light intensity was calibrated with an Orielmono-Si reference cell(CROWNTECH PVM 272 certificated by NREL).The surface roughness and morphology of PEDOT:PSS,PbI2, CH3NH3PbI3,CH3NH3PbI3/PCBM and CH3NH3PbI3/ P3HT:PCBM layers were characterized by Bruker INNOVA AFM in tapping mode.The thickness of above layer was measured by a surface profiler (KLA Tencor Alpha Step D-100).More detailed information on device fabrication and device characterization can be found in our previous paper[18].

Fig.1 (a)Schematic diagrams of the device structure for organic BHJ cell,perovskite cell and integrated cell.(b)Schematic energy level diagrams of each layer.

3 Results and Discussion

To understand the light absorption property of the integrated solar cells,the absorption spectra for CH3NH3PbI3/PCBM bi-layer film,P3HT:PCBM blend film and CH3NH3PbI3/P3HT:PCBM film weremeasured,as show in Fig.2.The thickness for CH3NH3PbI3film,PCBM film,P3HT:PCBM blend film and CH3NH3PbI3/P3HT:PCBM bi-layer is 260,80,100,360 nm,respectively.The absorption spectrum of the CH3NH3PbI3/P3HT:PCBM film shows a good accumulation of the respective absorption of CH3NH3PbI3film and the P3HT:PCBM BHJ blend film.

Fig.2 Absorption spectra of P3HT:PCBM blend film, CH3 NH3 PbI3/PCBM film and CH3 NH3 PbI3/P3HT: PCBM film,respectively.

Fig.3 J-V curves for the organic BHJ solar cells,perovskite solar cells,and the integrated solar cells,respectively.

The current density-voltage(J-V)curves of the integrated perovskite/BHJ solar cell,P3HT:PCBM BHJ solar cell as well as the single junction perovskite solar cell are shown in Fig.3.The detailed device performance parameters are summarized in Table 1.As shown in Fig.3 and Table 1,the integrated devices show higher performance than that of the pristine perovskite device due to the increased shortcircuit current(Jsc)and fill factor(FF).The reference perovskite device shows Jsc,open-circuit voltage(Voc),and FF of 10.3 mA/cm2,0.79 V, and 28.3%,respectively,leading to a PCE of 2.27%.The best integrated CH3NH3PbI3/P3HT: PCBM(100 nm)device gives a PCE of 6.54%, with a Jscof19.14mA/cm2,a Vocof0.76 V,and a FF of 45.0%.Accordingly,the improved performancemainly originates from the increased values of Jscand FF at the same time.Jscis higher than that of perovskite cells due to additional photocurrent contribution from the P3HT:PCBM bulk-heterojunction.

Table 1 Summary of device performances for the organic BHJ solar cells,perovskite solar cells and the integrated solar cells

Fig.4 AFM topographic images of the surfacemorphology of ITO/PEDOT:PSS(a),ITO/PEDOT:PSS/PbI2(b),ITO/PEDOT: PSS/CH3 NH3 PbI3(c),ITO/PEDOT:PSS/CH3 NH3 PbI3/PCBM(d),and ITO/PEDOT:PSS/CH3 NH3 PbI3/P3HT: PCBM(e)films,respectively.

In order to conducta deeper insight into the enhancement in the performance,we investigated the morphology of devices by AFM.Fig.4 shows the AFM images of the surface morphology of PEDOT: PSS,PbI2,CH3NH3PbI3,CH3NH3PbI3/PCBM,and CH3NH3PbI3/P3HT:PCBM films measured over an area of 5μm×5μm.Fig.4(a)shows the topographic images of PEDOT:PSS film spin-coated on the ITO electrode.Raand RMS roughness is 2.47 and 3.11 nm,respectively.The surface of the Pb I2on the PEDOT:PSS film(Fig.4(b))is a rougher morphology with a RMS roughness of 12.5 nm.

Next,we measured the topographic images of the CH3NH3PbI3layer prepared on PEDOT:PSS. RMS roughness is increased to about20.5 nm(Fig. 4(c)),Fig.4(d)and 4(e)display CH3NH3PbI3/ PCBM and CH3NH3PbI3/P3HT:PCBM bi-layer on the surface of ITO/PEDOT:PSS,respectively.The surface of the CH3NH3PbI3/P3HT:PCBM film was smooth than CH3NH3PbI3,with Raand RMS roughness of 13.7 and 17.5 nm,respectively.In contrast, amuch rougher surface with a RMS roughness of 55.4 nm is observed for CH3NH3PbI3/PCBM layer.The surface morphology image indicates that the introduction of P3HT interlayer into a CH3NH3Pb I3/PCBM planar heterojunction device has positive effect on the surface roughness.Consequently,a better charge transport interface is expected to form between CH3NH3PbI3film and P3HT:PCBM organic active layer.As a result, the performance of CH3NH3Pb I3/PCBM planar heterojunction device is improved.Higher photocurrent density and PCE would be expected by further device optimization.Moreover,by applying suitable low band gap high-performance polymers and optimizing perovskite device structure, much higher PCE can bemade.

4 Conclusion

In summary,an integrated solar cell combining a perovskite solar cell and an organic BHJ solar cell is investigated.Compared with the control perovskite planar device structure,the addition of an organic BHJ layer broadens the photoresponse of perovskite solar cell and improves themorphology of the interfacial layer.The best integrated CH3NH3PbI3/P3HT:PCBM device gives a PCE of 6.54%,with a Jscof 19.14 mA/ cm2,a Vocof 0.76 V,and a FF of 45.0%.The improved performance mainly originates from the increased values of Jscand FF at the same time. Therefore,enlarged photoresponse and enhanced photocurrent benefit from bulk heterojunction.By applying suitable low band gap high-performance polymers and optimizing perovskite device structure, much higher PCE can bemade.

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唐彤(1990-),男,湖南寧鄉(xiāng)人,碩士研究生,2012年于湖南師范大學(xué)獲得學(xué)士學(xué)位,主要從事有機(jī)光電材料與器件的研究。

E-mail：qingyi5173@163.com

楊利營(1973-),男,河北石家莊人,研究員,2002年于天津大學(xué)獲得博士學(xué)位,主要從事有機(jī)光電功能材料與器件的研究。

E-mail：liyingyang@tjut.edu.cn

高效鈣鈦礦-有機(jī)本體異質(zhì)結(jié)雜化串聯(lián)太陽能電池

唐 彤1,2,左紅文1,2,王亞凌1,2,秦文靜1,2,曹煥奇1,2,楊利營1,2*,姚 聰3*,葛子義4*,印壽根1,2*

(1.天津理工大學(xué)顯示材料與光電器件教育部重點實驗室,天津 300384; 2.天津理工大學(xué)天津市光電顯示材料與器件重點實驗室,天津 300384; 3.中國電子科技集團(tuán)第18研究所,天津 300384; 4.中國科學(xué)院寧波材料所,浙江寧波 315201)

制備了一種有機(jī)鉛鹵鈣鈦礦-有機(jī)本體異質(zhì)結(jié)雜化串聯(lián)太陽能電池。采用紫外可見吸收光譜、原子力顯微鏡對薄膜形貌進(jìn)行了表征。結(jié)果表明：有機(jī)本體異質(zhì)結(jié)層可以有效改善鈣鈦礦的表面形貌,增強(qiáng)了可見光的吸收。優(yōu)化后的串聯(lián)結(jié)構(gòu)電池的短路電流可達(dá)19.14 mA/cm2,開路電壓為0.76 V,光電轉(zhuǎn)換效率達(dá)到了6.54%。鈣鈦礦電池和有機(jī)本體異質(zhì)結(jié)電池串聯(lián)結(jié)構(gòu)可以同時提高短路電流及填充因子,二者具有較好的相容性和協(xié)同作用。

鈣鈦礦;本體異質(zhì)結(jié);串聯(lián)電池

1000-7032(2015)09-1047-06

2015-06-05;

2015-07-17

天津市自然科學(xué)基金(13JCYBJC18900,13JCZDJC26700);863國家高技術(shù)研究發(fā)展計劃(2013AA014201)資助項目

TM914.4 Document code：A

10.3788/fgxb20153609.1047