Preparation And Performance Improvement Of Rubrene/C₇₀ Organic Solar Cells

In this thesis, small-molecule organic solar cells with Rubrene/C₇₀as active layer werefabricated by thermal evaporation. Three aspects as follows were studied in depth:1. Four kinds of organic solar cells （OSC_s） were fabricated. Four different structures wereITO/MoO₃/CuPc/C₆0/BCP/Al；ITO/MoO₃/CuPc/C₇₀/BCP/Al；ITO/MoO₃/Rubrene/C₆0/BCP/Al；ITO/MoO₃/Rubrene/C₇₀/BCP/Al, respectively. The properties of the four devices were compared.The results showed that the short-circuit current density （JSC） of the OSC_s with C₇₀replaced C₆0as acceptor was increased significantly, while the open-circuit voltage （VOC） of the OSC_s withRubrene replaced CuPc as donor was increased drastically. Therefore, the power conversionefficiency （PCE） of the OSC_s was enhanced by275.4%.2. Optimization of Rubrene/C₇₀heterojunction solar cells was investigated. First, MoO₃andBCP were used as electrode modified layer, which led to a significant increase in theperformance of the OSC_s devices. Then the thicknesses of the active layer were optimized. Theresults showed that the optimum thicknesses of Rubrene layer and C₇₀layer were determined as30nm and25nm, respectively. The VOC, JSC, FF and PCE of the device after optimization were0.82V,2.025mA/cm2,49.8%,0.806%, respectively.3. The OSC_s devices with the structure of ITO/MoO₃/Rubrene/C₇₀/BCP/Al were fabricated.The degradation of the OSC_s devices was also investigated. The relationship between time andVOC, JSC, FF and PCE of the devices was investigated by testing the J-V characteristics. Theresults showed that the VOChardly changed with time, while the JSC, FF, PCE decreasedcontinuously with the increase of the time. Oxygen was thought to be the major factor causingthe degradation of OSC_s. Oxygen can infiltrate into the active materials and may react with C₇₀in cells, thus causing the decrease in conductivity of C₇₀and the increase in series resistance ofthe device. The oxidation of the C₇₀would be accelerated under light irradiation as well as theincreasing temperature accompany, thus accelerating the degradation of the device.