Design And Photovoltaic Performances Study Of Organic Solar Cells

Organic solar cells(OSCs) are potential low-cost alternative to their conventional inorganic counterpart due to their ease of processing and compatibility with flexible substrates and have been drawn much attention in recent years. Maximal power conversion efficiencies(PCE) of OSCs have reached above 10%. However, further improvement of PCE is required for commercialization due to the PCE of OSCs is still much smaller than that of inorganic solar cells. In this thesis, we study physical mechanism and design novel structure of small molecular weight organic solar devices for improving their efficiency.1. We have studid the photovoltaic(PV) performance of small molecular solar cells based on bulk heterojunction(BHJ) devices with small ratio donors doped in C60 matrix. A series of donor materials such as NPB、CBP、m-MTDATA、Cu Pc and TCTA are blended with C60 by different ratio. The optimum PCE is obtained at a rather low donor ratio of 5%. PCE of BHJ cell based on NPB donor reaches 2.25%, which is double of that of the planar heterojunction(PHJ) cell. We obtain that ΔEHOMO(HOMOC60–HOMOdonor) between C60 acceptor and donors would offer a maximal influence on achieving maximal PCE and an optimal ΔEHOMO locates around 0.8 e V. Besides, highly efficient organic tandem solar cell with peak PCE of 7.66% has been demonstrated by simply stacking two same Sub Pc:C70 bulk heterojunction devices, with a high active inter-connecting layer composed of Bphen/Ag/F16 Cu Pc/Mo O3. We find that F16 Cu Pc plays an important role in the inter-connecting layer. Thin F16 Cu Pc film extends the recombination zone, facilitates the extraction of hole and the carrier recombination. The measured PCE of the tandem solar cell is 7.66%,which corresponds to a 38% increase compared to that the optimal single cell.2. We demonstrate a highly efficient inverted small molecular solar cell with integration of Ag nanoparticles(NPs) into the devices. The optimized device based on thermal evaporated Ag NPs provides a PCE of 4.87%, which offers 33% improvement than that of the reference device without Ag NPs. Such a high efficiency is mainly attributed to the improved electrical properties by virtue of the modification of the surface of ITO with Ag NPs and the enhanced light harvesting due to localized surface plasmon resonance(LSPR).3. We studied the effect of electrode buffer layer on the performance of organic solar cells. A compound layer of Bphen/Mo O3 is firstly introduced to the cathode side as a cathode buffer layer(CBL). Such a compound CBL greatly extends device PCE and stability simultaneously compared with the traditional Bphen CBL. What is maore, high-efficiency Sub Pc/C60 based small molecular PHJ organic solar cells with CBP as anode exciton blocking layer(EBL) have been demonstrated. Through inserting 2 nm CBP before the donor Sub Pc, Jsc of OSCs exhibits a significantly increase by 41% from 5.32 to 7.53 m A/cm2 while the FF and VOC remain constant, resulting in a substantial enhancement in the PCE from 3.48% to 5.01% due to the exciton blocking effect of CBP at anode side. Evidence for anode exciton blocking effect of CBP is observed by photoluminescent spectra and some other methods.