Fabrication And Study Of Flexible Organic Solar Cells Based On Microcavity Structure

In this paper, the stable and high performance flexible microcavity organic solar cells based on P3HT: PCBM photoactive layer using bimetal electrode structure were fabricated, which is aiming at solving the problems of low efficiency and poor mechanical bendability of flexible devices. The main research contents include the following four parts:（1） In order to obtain high performance flexible organic solar cells, the relationship between the device performance and the preparation parameters was systematic studied, including the film thickness, drying time, annealing temperature of the active layers. It was found that the efficiency of the devices is more dependent on the drying time rather than the film thickness. It was found that thicker film needed higher annealing temperature with similar time in order to attain high efficiency. In addition, longer drying time of thicker devices led to an enhanced self-organization in the active layer. With the coherent effect of the preparation parameters, a maximum power conversion efficiency of 4.63% was achieved.（2） In the bottom-illuminated flexible devices, the Ag thickness of the semitransparent anode is optimized to be 16 nm, so that the optical and electrical properties can be well balanced, the maximum efficiency is 2.33%（Voc=0.567 V,Jsc=6.70 m A/cm2,FF=0.613）. In order to improve the transmittance of films, multiple layers of molybdenum oxide（MoO₃）/Li F/MoO₃/Ag/MoO₃ were used as transparent electrode, where the thin Ag layer yields high conductivity and the dielectric layer MoO₃/Li F/MoO₃ has high transparency due to optical interference. The power conversion efficiency（2.77%） was increased about 1.19 times, compared with indium tin oxide（ITO） based devices（2.18%）. The multilayer MoO₃/LiF/MoO₃/Ag/MoO₃ can improve the light transmittance and also facilitate charge carrier extraction. Such an electrode shows excellent mechanical bendability with a 9% reduction of efficiency from 2.76% to 2.51% after 1000 cycles of bendings due to the ductile nature of the thin metal layer and dielectric layer used.（3） In the top-illuminated flexible devices, the MoO₃/LiF/MoO₃ structure with high and low refractive index is used to increase transparency of the thin Ag top electrode, the Jsc can be improved from 5.82 m A/cm2 to 6.19 m A/cm2, the maximum efficiency is 2.10%. The device exhibits excellent mechanical flexibility in different bending directions, and the efficiency only decreased 8.4% and 9.6% after 1000 cycles of bendings. The results show that the MoO₃/Li F/MoO₃/Ag multilayer electrode structure is also suitable for the top-illuminated flexible microcavity devices.（4） In order to study the effect of microcavity, a high refractive index Al2O₃ layer fabricated by UV-ozone treatment（UV） was introduced between electrode and MoO₃ layer. After optimizing the UV time of Al layer, the efficiency of the device（2.66%） with MoO₃/Al-UV/Ag electrode was 1.19 times higher than the device（2.24%） with thin Ag of single layer electrode. In addition, the MoO₃/Al-UV/Ag electrode device efficiency decreased from 2.65% to 2.49%（lost 6%） of the 1000 cycles of bendings. This electrode structure improves the efficiency and mechanically stability of the devices.