Study On PCDTBT:PC₇₁BM Based Organic Polymer Solar Cells

Due to global warming and environmental degradation are becoming worse and worse, so we can’t wait to the development of new renewable energy, solar energy has becoming the main study of object. At the same time, organic solar cells（OSCs） caused widely attention and research, because of its preparation process is simple, low cost, flexible and can be producted in a large area, and so on. However,the low power conversion efficiency and the poor stability of organic solar cells become the major obstacle to realize its development. In order to improve stability and performance of devices, researcher hope to have breakthrough on the optimization of structure and looking for new materials. The experiment of paper to improve the efficiency and the stability of organic solar cells, the main research contents and conclusions are as follows:（1） This paper focus on the bulk heterojunction organic solar cell(ITO/PTFE/PCDTBT:PC₇₁BM/buffer layer/Al), mainly researched the cathode buffer layer to improve the performance of the device. The experiment used three different cathode buffer layer of lithium fluoride（LiF）, BCP and tris（8-hydroxyquinoline） aluminium（Alq₃） and adopted vacuum evaporation method to deal with three kinds of materials. By carrying out a series of characterizations including J-V and IPCE curve, we find that Alq₃ as cathode buffer layer, the performance of device is best, and the Jsc from 10.81 mA/cm2 increased to 12.27 mA/cm2, improved 41%, the FF from 51% increased to 59%, so the energy conversion efficiency reached 6.61%, because the Alq₃ has good the capability of electronic transmission. By atomic force microscopy（AFM） image see Alq₃ form a uniform thin film in vacuum evaporation, Alq₃ interlayer facilitates carrier transmission and effectively prevents the cathode atoms from diffusing into the active layer. Moreover, comparing the four groups of devices with Alq₃ buffer layer show better air-stability.（2） In this experiment, we fabricate solar cells based on PCDTBT（Poly[[9-（1-octylnonyl）-9H-carbazole-2,7-diyl]-2,5-thiophenediyl-2,1,3-ben zothiadiazole-4,7-diyl-2,5-thiophenediyl]） and PC₇₁BM([6,6]-phenyl-C₇₁-butyric acid methyl ester) as the active layer material, high boiling point solvents o-dichlorobenzene（ODCB） as the benchmark solvent, doped with three different volume of organic solvent, namely three chlorobenzene（TCB）, chlorobenzene（CB） and chloroform（CF）. By carrying out a series of characterizations including J-V and IPCE curve, we find that OSCs add a suitable mixed solvent will increase its power conversion efficiency. Comparing with the three devices of different mixing ratios, when using ODCB and CF mixed, the performance of device is best.（3） Experiments took CF dedoping of ODCB impact on device performance, mixed solvent deal with the film of active layer, which was scanned AFM and transmission electron microscopy（TEM）. We found two organic solvents with different boiling points and volatile degrees, so we have taked appropriate mixing ratio, the film of the device is better. And we test the impedance spectroscopy, absorption performance and electron mobility, When the solvent volume of 90% OACB doped with 10% CF, the device have the minimum of impedance and the preferably of absorbing, electron mobility reaches 5.83x10-3 cm2V-1s-1. Because of mixed solvent make the film form a good phase separation and be beneficial to exciton separation and transfer, thereby enhancing power conversion efficiency of the device.