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Morphology Control of Solution Processed Photo-active Layer for the Utilization of Organic and Organic-inorganic Hybrid Solar Cells

Title
Morphology Control of Solution Processed Photo-active Layer for the Utilization of Organic and Organic-inorganic Hybrid Solar Cells
Authors
XIE, LIN
Issue Date
2017
Department/Major
대학원 화학·나노과학과
Publisher
이화여자대학교 대학원
Degree
Doctor
Advisors
김경곤
Abstract
나의 논문은이 프로젝트가 대안적인 순차적 인 용액 증착 방법을 적용하여 유기 태양 전지의 새로운 새로운 제조 방법을 개발하는 것을 목표로하고 있음을 보여준다. P3HT / PCBM 및 PONTBT / PCBM에 기초한 SqD 태양 전지가 조사되었다. BSD 공정 태양 전지에 비해 SqD 처리 태양 전지는 뛰어난 안정성과 성능을 제공합니다. 최적화는 SqD mehod에 다양한 첨가물을 적용함으로써 더욱 유연하게 할 수 있습니다. 벌크 헤테로 접합 기능의 메커니즘을 더 잘 이해하기 위해서는 SqD 방법을 사용해야합니다. Perovskite 태양 전지 공정은 강하고 약한 배위 첨가제를 사용하여 조사되었다. 페 로브 스카이 트 필름의 형상은 강하거나 약한 배위 첨가제에 의해 조절 될 수있다. 페 로브 스카이 트 결정의 다른 성장 메커니즘이 밝혀졌습니다. 결론적으로, 중간상은 페 로브 스카이 트 태양 전지를 준비 할 필요가 없다.;In chapter 1, the general introduction and working principle of organic solar cells (OSCs) are presented for understanding of the present research. I introduced the sequential solution deposition process, which established as an alternative process for fabrication the highly efficient OSCs. Perovskite solar cells have recently been developed as a novel photovoltaics class. The evolution and working principle are introduced in the chapter 1 as well. In chapter 2, OSC based on P3HT/PCBM are fabricated using a SqD process. The film morphology and solar cell performance is investigated by changing the thickness of PCBM layer. Based on the water contact angle and PL measurements, most of the PCBM was diffused into the amorphous P3HT region after thermal annealing. The EQE reveals that the morphology of the P3HT in the SqD solar cell is crystalline, even without thermal annealing. The transient photovoltage experiments suggest that the morphology of P3HT and PCBM in the SqD solar cell reduces the charge recombination better than that in the BSD solar cell. The SqD solar cell exhibits a PEC of 3.54%, similar to that of the BSD solar cell. In chapter 3, OSCs based on an alkoxy naphthalene based polymer nanofiber/fullerene have been developed by SqD process. Spin-coating a polymer solution incorporated with 1-CN results in the formation of dense polymer nanofibers with diameters of 30-50 nm. The fullerene top layer is sequentially deposited onto the polymer nanofiber bottom layer to form a (BHJ) through the inter-diffusion of fullerene. The SqD processed OSC utilizing a polymer nanofiber/fullerene bilayer exhibits higher photocurrent density compared to those utilizing a plane polymer layer/fullerene bilayer. Optical, morphological and J-V investigations on the photo-active layers reveal that improved ordering of the polymer chain with proper direction and increased heterojunction area are the main contributors to the superior solar cell performance. These results suggest an efficient interdigitated BHJ morphology can be realized by a sequentially deposited, pre-formed nanofiber/fullerene bilayer without a thermal annealing process. In chapter 4, Both charge recombination and degradation in the sequential solution deposition processed polymer/fullerene OSC are effectively reduced by insertion of a TiO2 inter-layer between the active layer processed by SqD and Al electrode. The SqD film composed of P3HT bottom-layer and a PCBM top-layer shows significant change in morphology due to the substantial inter-penetration of P3HT and PCBM during thermal annealing process. Consequently, the active layer surface becomes P3HT rich resulting in a significant charge recombination at the bilayer/Al interface of SqD OSC. The charge recombination rate of the SqD OSC is reduced by one order of magnitude upon the insertion of a TiO2 nanoparticle inter-layer between the bilayer and the Al electrode after the thermal annealing process. In contrast, when the thermal annealing process is conducted after insertion of the inter-layer, the effect of the TiO2 inter-layer becomes insignificant. The VOC and efficiency of the bilayer OSC is greatly enhanced from 0.37 V to 0.66 V and 1.2% to 3.7%, respectively, by utilizing the properly constructed TiO2 inter-layer in the SqD-OSC. Additionally, insertion of the TiO2 inter-layer significantly improves the stability of the OSC. The SqD OSC with a TiO2 inter-layer maintains 57% of its initial PCE after storage under dark ambient conditions for 700 hours without encapsulation, whereas the SqD OSC without a TiO2 inter-layer maintains its solar cell performance for only 200 hours under the same conditions. In chapter 5, a ternary solvent system consisting of dimethyl sulfoxide (DMSO), γ-butyrolactone (GBL) and N-Methyl-2-pyrrolidone (NMP) to improve the uniformity of CH3NH3PbI3 (MAPbI3) perovskite domains have been developed. Compared to MAPbI3 perovskite film prepared by the binary solvent consisting of DMSO and GBL, the surface roughness and uniformity of the MAPbI3 film is greatly improved by using the ternary solvent system. The thermogravimetric analysis reveals that the NMP-PbI2-MAI intermediate, DMSO-PbI2-MAI intermediate and MAPbI3 crystals are co-existed in the as cast MAPbI3 films. Furthermore, it is found that the thermal stability of intermediate phases and the solvent evaporation rate are critical for the nucleation of the perovskite crystals during the thermal annealing treatment. The thermally stable intermediates prepared with the ternary solvent converted to MAPbI3 film with a highly uniform and smooth surface. The film forms intimate contact with charge transporting layer when the layer is applied as a photoactive layer in the solar cell. As a result, the power conversion efficiency of ternary solvent processed solar cells is enhanced by 38.2% compared to that of binary solvent processed one. Furthermore, the stability of the ternary processed perovskite solar cells are greatly improved, as well. This investigation provides better understand the role of different processing solvents or additives in effecting the perovskite film quality. In chapter 6, despite tremendous progress in studying of solvent engineering process in perovskite solar cells with the DMSO, there has been a lack of information on perovskite film formation with different coordination capability additives. I report here that perovskite solar cells successfully fabricated with DMI which has a weak coordination capability with PbI2, involving a non-intermediate phase in whole fabrication of perovskite solar cells. As illustrated from the XRD and AFM, in the non-intermediate perovskite solar cells, well fast ordered growth of perovskite crystal enable to promote an extremely smooth surface of perovskite film and a perovskite film with large crystal size (over 1μm). The PL and light intensity measurements results revealed that longer carrier life time and less recombination is obtained in the perovskite solar cells by employing the DMI. The power conversion efficiency was enhanced from the 15.8% to 17.6 % by using the DMI compared with the one processed with DMSO. Particular, I have also proved that the fabrication of perovskite solar cells with weak coordination additive enable to process in a wide stoichiometric ratio between the PbI2 and DMI.
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