| Organic solar cells has been widespread concerned for its advantage. As an important part of organic solar cells, polymer solar cells are of low coat, easy processing, flexible. Currently, some extraordinary power conversion efficiency of polymer solar cells are over 10%. To enhance the power conversion efficiency of organic solar cells,the study of interfacial modifications and interfacial processes becomes a hot topic. The study on the buffer layer of polymer solar cells is good for both traditional solar cells and other types of solar cells. In this study, several types of materials are used as anode buffer layer materials to modify the anode of polymer solar cells, test their performances and analysis the theories. V2O5 nanowire, PbS quantum dots and DNA-CTMA are produced as buffer layers by all solution processing method to modify the anode of polymer solar cells. Those buffer layers improve the hole transition, light absorption, which lead to improvement of device performances. DNA-CTMA doped with PSS(DNA-CTMA:PSS) which has similar performance as PEDOT:PSS are proved as a promisingly alternative of traditional anode buffer layer of PEDOT:PSSAt first, we introduced the background, working principle, performance parameters of solar cells and the types of solar cells. Highlighted the development of anode buffer layer of polymer solar cells. The study of anode buffer layer of polymer solar cells is on PEDOT:PSS, treatments of PEDOT:PSS, other organic materials, self-assembled monolayers and inorganic materials. At last,the purposes and the innovations of this thesis are given.Secondly, experimental instruments, measuring instruments and fabrication method of polymer solar cells were introduced in chapter 2. Experimental instruments includes spin coater, ultrahigh vacuum organic/inorganic thermal evaporation deposition system. And measuring instruments includes I-V measurement instrument, external quantum efficiency(EQE) measurement system, ultraviolet and visible spectrophotometer(UV-Vis), and electrochemical workstation. The fabrication methods of polymer solar cells includes ITO substrates cleaning, oxygen plasma treatment, spin coating buffer layer(active layer), and depositing Al cathode.In the beginning of this study,a high performance organic-inorganic polymer photovoltaic device with double-decked anode buffer layer sandwiched between indium tin oxide(ITO) and the photoactive layer is reported. The double-decked buffer layer is fabricated by coating vanadium oxide(V2O5) nanowire on top of the PEDOT:PSS layer and the reported device has the structure of ITO/PEDOT:PSS/V2O5/P3HT:PCBM/Al. The power conversion efficiency(PCE) of polymer photovoltaic cells with the hybrid buffer layer is improved by 14.10% compared to the polymer photovoltaic cell commonly employed PEDOT:PSS hole transporting material; and PCE of this proposed polymer photovoltaic cell is improved by 30.40% compared with the polymer photovoltaic cell employed V2O5 powder as buffer layer. The improvement of PCE is mainly caused by the elevation of short circuit current density(Jsc) instead of the open circuit voltage(Voc). Experimental results show that layer of V2O5 nanowires can not only block electron from wrong directions efficiently,but also increase incident light paths in the hybrid buffer layers due to refraction and reflection. And pseudo texturing effects of V2O5 nanowires which result in higher photon absorptivity of the photoactive layer make polymer photovoltaic cells with this double-decked buffer layer outperform that with buffer layers constructed by either PEDOT:PSS or V2O5 nanowires only.The device with V2O5 nanowires got good performance. In a lot of reports, as a different structure from nanowires, quantum dots can also be used as anode buffer layer without texturing effects. We prepared PbS quantum dots, with oleic acid(OA) and octylamine(OCA) ligands, tested the light absorbance and observed the micro-morphology. PbS quantum dots was doped into P3 HT, PCBM and spin coated on ITO as anode buffer layer. The doping of PbS quantum dots into P3 HT, PCBM can expand the infrared absorption. The exciton generated by PbS quantum dots can be more effectively dissociated, because PbS quantum dots formed built-in field with the interfaces of P3 HT, PCBM and Al. Inserting PbS quantum dots between ITO and PEDOT:PSS, made the ITO anode more smooth and isolated PEDOT:PSS which is strongly acidic(PH=1.4). The structure of device in this work is ITO/PbSQDs/PEDO T:PSS/P3 HT, PCBM, PbSQDs/Al. Comparing with the devices without quantum dots, PCE was increased by 30.40%, Voc was increased by 4.76% was increased by 22.55%. PbSQDs devices had higher light absorbance in 300 to 700 nm comparing with traditional device. And significant increase of external quantum efficiency(EQE) in 500 nm are obtained.The two kinds of materials tried before both enhanced the performance of polymer solar cells. But V2O5 nanowires and PbS are synthetics and are toxic for people. So that we tried DNA which is a kind of biomaterials as anode buffer layer. Deoxyribonucleic acid(DNA) – cetyltrimethyl ammonium(CTMA) is spinning coated on top of poly(3, 4-ethylenediox-ythiophene) doped with poly(styrene-sulfonate)(PEDOT:PSS) to fabricate a new type of bio-organic polymer solar cells(PSCs) with a structure of ITO/PEDOT:PSS/DNA-CTMA/P3HT: PCBM/Al by an all-solution method. Power conversion efficiency(PCE) of the proposed bio-organic PSCs with PEDOT:PSS/DN A-CTMA buffer layer are improved by 146.85% compared to PSCs with DNA-CTMA anode buffer layer only; PCE of this proposed photovoltaic cell is improved by 13.14% compared with PSCs commonly employed PEDOT:PSS as hole transporting material; and the PCE of the propose PSCs is very similar to the devices with PEDOT:PSS buffer layer doped with V2O5 nanowires. Growth of PCE is mainly driven by the enhancement of short circuit current density(Jsc). Though photo-absorption of the proposed bio-organic polymer solar cells decreases, significant increase of external quantum efficiency(EQE) from 350 to 550 nm are obtained due to the unique photonic and optical properties derived from double-helix structures. Compared to V2O5 nanowires dopant, DNA-CTMA nanowires is innocuous and inherently biodegradable.Although PEDOT:PSS/DNA-CTMA bi-layer have good performance in polymer solar cells, but it still can’t get rid of PEDOT:PSS. Deoxyribonucleic acid(DNA) – cetyltrimethyl ammonium(CTMA) doped with poly(styrene-sulfonate)(PSS) was used to replace poly(3,4-ethylenediox-ythiophene): poly(styrenesulfonate)(PEDOT:PSS) to fabricated a new bio-organic anode buffer layer and the characteristics of these all solution-processed solar cells was investigated in this paper. Voc,Jsc,FF,and power conversion efficiency(PCE) were measured under 100 mW/cm2(AM 1.5) solar simulator irradiation. Compared to polymer solar cells employed PEDOT:PSS as hole transporting material,Jsc of the bio-organic photovoltaic cells using DNA-CTMA:PSS as anode buffer layer increased by 9.20%; and PCE of the bio-organic photovoltaic cell was improved by 0.64%. Enhancement of PCE was mainly driven by the improvement of short circuit current density(Jsc). Significant increase of external quantum efficiency(EQE) from 420 to 570 nm and transmittance from 620 to 800 nm were obtained due to its unique photonic and optical properties derived from double-helix structures. Besides the similar electronical performance, the inherently biodegradable and renewable features indicated DNA-CTMA:PSS as one of the promising alternative materials to PEDOT:PSS as anode buffer layer for polymer solar cells.Finally, the work of this article is summarized and pointed out the inadequate. Also gives the outlook of the future work. |
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