OPTIMIZATION OF ORGANIC SOLAR CELLS (OPV DEVICES) BASED ON THE SEMICONDUCTOR POLYMERS MEH-PPV, P3HT AND PIDT-PHANQ USING PCBM AS ELECTRON ACCEPTOR
JOSE FRANCISCO SALINAS TORRES
"Organic solar cells (OPV devices) are a new sort of photovoltaic devices whose reduced manufacturing cost and facility of fabrication will contribute to solve our dependence on fossil fuels, main reason of the current high levels of greenhouse gases and global warming. In this thesis several approaches were considered to unlock the full potential of organic solar devices: i) A low melting point eutectic alloy (Wood’s metal) was used as substitute of evaporated aluminum allowing the manufacture of solar cell devices by a free vacuum steps process. Our method proved to be adequate to quickly test the photovoltaic performance (PCE = 0.8 %) of OPV cells based on MEH:PPV and an organo-boron molecule synthesized in our group. ii) For both methods (with and without vacuum steps) and using the conventional and inverted architectures, the photovoltaic behavior of OPVs based on the polymer P3HT was compared. Devices prepared under ambient conditions reached efficiencies as high as 2.2% employing the inverted architecture and 1.8% using Wood’s metal. iii) A thin film optical simulator was developed to provide an optimization route for the development of high-performance solar cells based on ultra-thin silver films. The simulations were in good agreement with the experimental results, allowing the design of a micro-cavity based device of superior performance (PCE = 6.56% using PIDT-PhanQ) even compared to devices using ITO. iv) The optical simulator was employed on the design of semitransparent organic devices; by adequately choosing materials and electrodes, solar cells of neutral appearance were developed. The color quality was analyzed using the CIE 1931 color space. v) High performance semitransparent solar cells (PCE = 7.56%, using PBDTTT-C-T, Ag: 60 nm) were developed using a wide absorption polymer. Window application was evaluated by analyzing the color rendering index. For several degrees of transparency, neutral appearance with respect to the human eye was achieved. The color rendering indexes were the highest reported for organic solar devices (CRI = 97.3, Ag: 18 nm). Transparencies as high as 37.3 % with respect to the human eye were possible reducing the Ag thickness to 6 nm."