表面配体和器件结构对PbS胶体量子点电池性能的影响
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摘要
利用吸收光谱、傅里叶变换红外光谱和循环伏安等表征技术,分析了利用四丁基碘化铵(TBAI)和1,2-乙二硫醇(EDT)配体钝化处理的PbS胶体量子点的光学性质、表面化学及其能级结构,并在此基础上分别以PbS-TBAI薄膜、PbS-EDT薄膜和PbS-TBAI/PbS-EDT薄膜作为有源层制备了PbS胶体量子点/Zn O纳米粒子异质结太阳能电池,以比较研究表面配体和器件结构对器件光伏性能及其稳定性的影响。结果表明,TBAI和EDT均能与PbS胶体量子点表面原有的油酸配体实现良好置换,但是配体置换之后量子点表面均残留少量油酸分子; PbS-TBAI薄膜的导带底为-5.12 eV,价带顶为-3. 86 eV,而PbS-EDT薄膜的导带底为-4. 99 eV,价带顶为-3. 74 eV,后者相对前者出现了明显的能带上移; PbS-TBAI/PbS-EDT双配体器件的光伏性能最优,能量转化效率达到4. 43%;随着空气暴露时间的增加,PbS-TBAI/PbS-EDT双配体器件和PbS-TBAI单配体器件表现出相似的性能变化趋势,于3 d后达到最优光伏性能,而PbS-EDT单配体器件的空气稳定性差,3 d后的能量转换效率下降至初始效率的1/4。本工作的研究结果将不仅有助于加深对PbS胶体量子点电池性能变化规律的认识,而且有望促进该类电池制备技术的进一步优化。
The optical properties,surface chemistry and band energies of PbS colloidal quantum dots (CQDs) passivated with tetrabutylammonium iodide (PbS-TBAI) and 1,2-ethanedithiol (EDT) were analyzed by absorption spectroscopy,Fourier transform infrared spectroscopy and cyclic voltammetry measurements. Also,the photovoltaic performance and air stability of PbS CQDs/Zn O nanoparticles heterojunction solar cells using PbS-TBAI,PbS-EDT and PbS-TBAI/PbS-EDT films as active layers respectively were investigated. The results showed that both TBAI and EDT ligands could achievegood ligand exchange with original oleic acid ligands on the surface of PbS CQDs,while a small number of residual oleic acid molecules remained in the PbS CQDs films. The conduction band minimum and valence band maximum of the PbS CQDs treated with TBAI are-3. 86 eV and-5. 12 eV,while they can be upshifted to-3. 74 eV and-4. 99 eV,respectively,for the PbS CQDs treated with EDT. The PbS-TBAI/PbS-EDT device exhibited the highest power conversion efficiency of 4. 43% among these three type of devices. With the increase of air exposure time,the PbS-TBAI/PbS-EDT device exhibited similar performance evolution to the PbS-TBAI device and achieved its best performance after three days of air exposure. However,the PbS-EDT device showed poor air stability and its efficiency was reduced to a quarter of its initial value after three days of air exposure. This work is not only capable of deepening the understanding of the performance evolution of PbS-CQD solar cells,but also capable of guiding the further optimization of these devices.
The optical properties,surface chemistry and band energies of PbS colloidal quantum dots (CQDs) passivated with tetrabutylammonium iodide (PbS-TBAI) and 1,2-ethanedithiol (EDT) were analyzed by absorption spectroscopy,Fourier transform infrared spectroscopy and cyclic voltammetry measurements. Also,the photovoltaic performance and air stability of PbS CQDs/Zn O nanoparticles heterojunction solar cells using PbS-TBAI,PbS-EDT and PbS-TBAI/PbS-EDT films as active layers respectively were investigated. The results showed that both TBAI and EDT ligands could achievegood ligand exchange with original oleic acid ligands on the surface of PbS CQDs,while a small number of residual oleic acid molecules remained in the PbS CQDs films. The conduction band minimum and valence band maximum of the PbS CQDs treated with TBAI are-3. 86 eV and-5. 12 eV,while they can be upshifted to-3. 74 eV and-4. 99 eV,respectively,for the PbS CQDs treated with EDT. The PbS-TBAI/PbS-EDT device exhibited the highest power conversion efficiency of 4. 43% among these three type of devices. With the increase of air exposure time,the PbS-TBAI/PbS-EDT device exhibited similar performance evolution to the PbS-TBAI device and achieved its best performance after three days of air exposure. However,the PbS-EDT device showed poor air stability and its efficiency was reduced to a quarter of its initial value after three days of air exposure. This work is not only capable of deepening the understanding of the performance evolution of PbS-CQD solar cells,but also capable of guiding the further optimization of these devices.
引文
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[2]KIM T,PALMIANO E,LIANG R Z,et al..Hybrid tandem quantum dot/organic photovoltaic cells with complementary near infrared absorption[J].Appl.Phys.Lett.,2017,110(22):223903-1-5.
[3]LAN X Z,VOZNYY O,DE ARQUER F P G,et al..10.6%certified colloidal quantum dot solar cells via solvent-polarityengineered halide passivation[J].Nano Lett.,2016,16(7):4630-4634.
[4]LóPEZ A B C,VEGA A M,LóPEZ A L.Next Generation of Photovoltaics[M].Berlin,Heidelberg:Springer,2012.
[5]BEARD M C.Multiple exciton generation in semiconductor quantum dots[J].J.Phys.Chem.Lett.,2011,2(11):1282-1288.
[6]PIETRYGA J M,PARK Y S,LIM J,et al..Spectroscopic and device aspects of nanocrystal quantum dots[J].Chem.Rev.,2016,116(18):10513-10622.
[7]SHULGA A G,PIVETEAU L,BISRI S Z,et al..Double gate Pb S quantum dot field-effect transistors for tuneable electrical characteristics[J].Adv.Electron.Mater.,2016,2(4):1500467.
[8]SUKHOVATKIN V,HINDS S,BRZOZOWSKI L,et al..Colloidal quantum-dot photodetectors exploiting multiexciton generation[J].Science,2009,324(5934):1542-1544.
[9]KAGAN C R,LIFSHITZ E,SARGENT E H,et al..Building devices from colloidal quantum dots[J].Science,2016,353(6302):aac5523-1-9.
[10]MCDONALD S A,KONSTANTATOS G,ZHANG S G,et al..Solution-processed Pb S quantum dot infrared photodetectors and photovoltaics[J].Nat.Mater.,2005,4(2):138-142.
[11]KIM G H,DE ARQUER F P G,YOON Y J,et al..High-efficiency colloidal quantum dot photovoltaics via robust self-assembled monolayers[J].Nano Lett.,2015,15(11):7691-7696.
[12]LIU M X,VOZNYY O,SABATINI R,et al..Hybrid organic-inorganic inks flatten the energy landscape in colloidal quantum dot solids[J].Nat.Mater.,2016,16(2):258-263.
[13]CAO Y M,STAVRINADIS A,LASANTA T,et al..The role of surface passivation for efficient and photostable Pb S quantum dot solar cells[J].Nat.Energy,2016,1(4):16035-1-23.
[14]MA W L,SWISHER S L,EWERS T,et al..Photovoltaic performance of ultrasmall Pb Se quantum dots[J].ACS Nano,2011,5(10):8140-8147.
[15]ZHAI G M,CHURCH C P,BREEZE A J,et al..Quantum dot Pb S0.9Se0.1/Ti O2heterojunction solar cells[J].Nanotechnology,2012,23(40):405401-1-7.
[16]王恒,翟光美,张继涛,等.Pb S量子点能级结构的尺寸和配体依赖性及其对异质结电池性能的影响[J].无机材料学报,2016,31(9):915-922.WANG H,ZHAI G M,ZHANG J T,et al..Pb S quantum dots:size,ligand dependent energy level structures and their effects on the performance of heterojunction solar cells[J].J.Inorgan.Mater.,2016,31(9):915-922.(in Chinese)
[17]LAN X Z,VOZNYY O,KIANI A,et al..Passivation using molecular halides increases quantum dot solar cell performance[J].Adv.Mater.,2016,28(2):299-304.
[18]CHUANG C H M,BROWN P R,BULOVIC'V,et al..Improved performance and stability in quantum dot solar cells through band alignment engineering[J].Nat.Mater.,2014,13(8):796-801.
[19]ZHAI G M,BEZRYADINA A,BREEZE A J,et al..Air stability of Ti O2/Pb S colloidal nanoparticle solar cells and its impact on power efficiency[J].Appl.Phys.Lett.,2011,99(6):063512-1-3.
[20]LIU D Y,KELLY T L.Perovskite solar cells with a planar heterojunction structure prepared using room-temperature solution processing techniques[J].Nat.Photon.,2014,8(2):133-138.
[21]HUANG Z,ZHAI G M,ZHANG Z M,et al..Low cost and large scale synthesis of Pb S quantum dots with hybrid surface passivation[J].Cryst Eng Comm,2017,19(6):946-951.
[22]解镕玮.Pb S、Fe S2纳米晶光电性能及在薄膜太阳能电池中的应用研究[D].太原:太原理工大学,2015.XIE R W.The Optoelectronic Properties and Applications in Thin Film Solar Cells of Pb S and Pyrite Fe S2Nanocrystals[D].Taiyuan:Taiyuan University of Technology,2015.(in Chinese)
[23]ZHAI G M,XIE R W,WANG H,et al..Effect of capping ligands on the optical properties and electronic energies of iron pyrite Fe S2nanocrystals and solid thin films[J].J.Alloys Compd.,2016,674:9-15.
[24]NING Z J,VOZNYY O,PAN J,et al..Air-stable n-type colloidal quantum dot solids[J].Nat.Mater.,2014,13(8):822-828.
[25]STAVRINADIS A,PRADHAN S,PAPAGIORGIS P,et al..Suppressing deep traps in Pb S colloidal quantum dots via facile iodide substitutional doping for solar cells with efficiency>10%[J].ACS Energy Lett.,2017,2(4):739-744.
[26]GAO W H,ZHAI G M,ZHANG C F,et al..Towards understanding the initial performance improvement of Pb S quantum dot solar cells upon short-term air exposure[J].RSC Adv.,2018,8(27):15149-15157.