【作者】 沈亮；

【导师】 陈维友；

【作者基本信息】 吉林大学 ， 微电子学与固体电子学， 2009， 博士

【摘要】 我们利用溶胶-凝胶法,通过烧结制备了纳米晶二氧化钛薄膜。使用聚3己基噻吩(P3HT)和水溶性聚噻吩(PEDOT)作为电子给体,二氧化钛(TiO2)作为电子受体,制作了异质结薄膜太阳能电池器件。我们探讨了激子形成机制,电子-空穴分离过程,电极收集电荷机理,材料的能级匹配。并对光电性能进行了比较,优化了器件厚度。为了提高器件的性能,使用二甲苯,氯仿,氯苯三种不同的溶剂溶解P3HT。我们使用AFM对P3HT的表面形貌进行了表征,发现二甲苯和氯仿溶解的P3HT的表面粗糙度很大,没有形成平整的薄膜。我们使用了聚乙二醇(PEG)掺杂TiO2溶胶,烧结后利用扫面电镜(SEM)和原子力显微镜(AFM)观察形貌,发现薄膜表面形成了很多纳米孔。这样大大提高了与导电聚合物的接触面积,有更多的激子产生在界面出分离,提高了器件的短路电流密度和能量转换效率。为了提高器件的性能,我们制作了三明治结构的器件,具体为ITO/TiO2/CuPc/P3HT/Au。酞菁铜(CuPc)是一种小分子P型有机材料。在400-500nm及600-700nm波段有两个吸收峰,而P3HT在500-600nm有一个强吸收峰。这样,整个器件的吸收谱拓展到整个可见光范围,大大提高了对光的利用率。CuPc的能级与TiO2和P3HT匹配,既是光敏化层又充当电子给体。当CuPc的厚度为20nm时,器件的性能达到最佳。在AM1.5G标准太阳光照下,开路电压Voc=0.6V,短路电流Isc=2.22mA/cm2,填充因子FF=0.45,能量转化效率PCE=0.66%。为了提高器件的性能,我们利用TiO2作为电子传输层,使用C60的衍生物PCBM与P3HT共混形成体异质结,选用CuPc作为空穴传输层,制作了反型的体异质结太阳能电池。光照下有源层产生电子-空穴对在界面处分离,作为N型半导体的纳米TiO2薄膜传导分离的电子至阴极,作为P型半导体的CuPc传导分离的空穴至阳极,减少了激子复合。CuPc作为一种小分子材料,迁移率高,提高光生电流;作为一种金属络合物,可以平整有源层表面的粗糙度,改善有源层与金属电极的接触,减小电池的串联电阻。当CuPc的厚度为10nm时,器件的性能达到最佳。开路电压Voc=0.54V,短路电流Isc=5.86mA/cm2,填充因子FF=0.53,能量转化效率PCE=1.65%。更多还原

【Abstract】 Our society is based on coal,oil and natural gas,but these fossil fuels will be depleted someday in the future because they are limited.Carbon dioxide is produced in the combusition has affected the consequence of climate,resulting in the global warming effect.Under these circumstances,interest in photovoltaic solar cells is increasing rapidly as an alternative and clean energy source.Photovoltaic solar cells provide clean electrical energy because the solar energy is directly converted into electrical energy without emitting carbon dioxide.The solar energy is not limited,free of charge and distributed uniformly to all human beings. Up to now, the photovoltaic cells based on inorganic materials (mainly silicon) have been proved to convert sunlight to electricity efficiently. But the high cost for manufacture limits them to be widely used. Organic and polymer solar cells, based on organic and polymer materials as active layer, possess the advantage of light weight, plenty of choices for active layer, flexibility, low cost and easily being large-scale etc., which attracts great attention in recent years.Under illumination, light is converted to electricity by polymer heterojunction solar cells through five processes sequentially, (i) photons are absorbed by the active layer and exitons form; (ii) excitons diffuse in the active layer; (iii) charge transfer when excitons reach donor/acceptor interface and electron-hole (e-h) geminate pair forms; (iv) e-h geminate pairs dissociate with field assisted and free charge carriers are produced; (v) finally, the free carriers are transported through their respective phases to the electrodes in order to be extracted. The photovoltaic performance of devices is strongly dependent on the light harvesting, energy levels of materials, the morphology of thin films, buffers near electrodes, and so on.This thesis is mainly discussing how the above factors such as device structure, morphology of thin films photovoltaic performance of organic/inorganic thin films heterojunction solar cells and inverted bulk-heterojunction solar cells. We used different polymer materials and organic small molecular CuPc materials, and investigated the relation between absorption spectrum of materials and device performance; We doped polyethylene glycol(PEG) of different concentration in TiO2 sol and investigated the relation between morphology of thin films and device performance. We evaporated CuPc as a buffer near gold electrode, and investigated the relation between the thickness of CuPc and device performance. More details are now listed below,1. For organic/inorganic thin film heterojunction solar cells, we used sol-gel method to fabricate nano crystalline TiO2 thin films by sintering as electron acceptor and used P3HT, water soluble PEDOT as electron donor. We make a research on exciton creating mechanism, electron-hole dissociation, charge collection, energy level matching of materials and so on. We compared the photovoltaic performance of different materials, and optimized the thin film thickness.We used different solvent ,including to Chlorobenzene, CHCl3, Xylence, to dissolve P3HT, and fabricated the solar cells. It is found that the performance of the device with P3HT dissolved with Chlorobenzene is better than that of two. AFM is used to compare the surface morphology, and the film of P3HT dissolved with Chlorobenzene is smoother than that of two.2. We doped polyethylene glycol(PEG) of different concentration in TiO2 sol, after sintering, SEM and AFM are used to observe the surface morphology. The thin film is porous.The contact area between TiO2 thin film and P3HT is bigger than that of without PEG, so there are more exciton can be generated and separated in the interface. The photocurrent and power conversion efficiency was improved .3. We fabricated the photovoltaic device of sandwich structure. CuPc is a kind of P type small material, which is applied widely in organic light emitting diodes. a new type of hybrid nanocrystalline solar cells was fabricated. The device structure is indium tin oxide (ITO)/ titanium oxide (TiO2)/ copper phthalocyanine (CuPc) / poly (3-hexylthiophene) (P3HT) /Au. In this architecture, TiO2 was designed to act as the electron acceptor, and P3HT was the electron donor. CuPc was used as a sensitizer to enhance the photon absorption. The results showed that by inserting CuPc layer between P3HT and TiO2 layers, the light absorption, excitons separation and photocurrent under white light were dramatically enhanced. The device has a short current density(JSC) of 1.15 mA/cm2 and power conversion efficiency(PCE) of 0.28% without CuPc layer. However, JSC and PCE turn to be 2.22mA/cm2 and 0.66% respectively with a 20nm thickness CuPc layer under white light illumination with an intensity of 100 mW/cm2.The performance improvement can be attributed to the higher carrier mobility and the stronger photon absorption using CuPc layer.4. A new type of inverted polymer solar cells was fabricated. The device structure was indium tin oxide(ITO)/ titanium dioxide (TiO2)/ regioregular poly-(3-hexylthiophene)(RR-P3HT): [6,6]-phenyl C60 butyric acid methyl ester (PCBM)/ copper phthalocyanine (CuPc)/Au. In this architecture, TiO2 was designed as an electron selective layer. CuPc, known as a sort of P type semiconductor material, was inserted between the active layer and top electrode to improve hole collection and transport. Without CuPc,short-circuit current of 4.22 mA/cm2, open-circuit voltage of 0.48V, filling factor is 0.48 and power conversion efficiency of 0.97% were obtained. Using an optimized CuPc layer of 10nm thickness, short-circuit current of 5.86 mA/cm2, open-circuit voltage of 0.54 V, filling factor is 0.53 and power conversion efficiency of 1.65% were obtained.更多还原