Application Of Scanning Probe Microscopy In Organic Solar Cells Research

Organic solar cells are a promising alternative for clean,renewable sources of energy,and offer the combined attraction of light-weight,flexibility and low cost to manufacture by large-area roll-to-roll processes.The relative low power conversion efficiency(PCE)of the photovoltaic devices and morphological instability are considered to be the major obstacles for commercialization.So,how to control the morphology of organic solar cells is of critical importance and rather challenging for the future commercial application.In this thesis,scanning probe microscopy has been used to study the relationship between the microstructure and macro properties of organic photovoltaic device,so as to optimize the device performance.Detailed work is as follows:First,the performance and morphology stability of polymer solar cells based on P3HT: ICBA or P3HT: PCBM system is compared.Effect of the different D/A weight ratios on photovoltaic performance of the P3HT: ICBA was studied.The optimal device achieved PCE of 5.51% with a Jsc of 10.86 mA/cm~2,Voc of 0.83 V,and FF of 61.1 % under100 mW/cm~2 illumination.However,the stability of P3HT: ICBA is less stable than that of P3HT: PCBM.Atomic force microscope(AFM)results revealed the morphology of the P3HT: ICBA film changed considerably during the storage periods due to unstable interpenetrating D-A network.The measured PL decay lifetime for P3HT: PCBM and P3HT: ICBA system is 33.66 ns and 35.34 ns,respectively,indicating that the latter has less efficient exciton separation efficiency than the former.We also present an approach to enhance the stability of P3HT: ICBA systems by adding PCBM as the second acceptor.Second,conductive AFM(C-AFM)was conducted to study the effect of ultraviolet ozone treatment with different treatment time on the surface electrical and optical properties of PEDOT: PSS film and on the performance of organic solar cell.We also use C-AFM to investigate the effect of substrate-preheating on the performance and conductive properties of perovskite films to optimize the preparation technology of perovskite solar cells.Third,the performance of solar cells based on multilayer of PEDOT: PSS/ CuNWs /PEDOT: PSS(PCP)as the buffer layer are investigated.By means of SPM,the surface morphology of PCP multilayer was analyzed.The organic solar cell fabricated on the PCP multilayer with 6mg/mL Cu NWs exhibits excellent device performances: a FF of 61 %,a Jsc of 11.21mA/cm~2,a Voc of 0.57 V,and a PCE of 3.90 %.This suggests that PCP multilayer is a promising candidate for low-cost and low-temperature processing fabrication of organic solar cells.