Study Of Polymer Solar Cells Using Tungsten Oxide As Anode Buffer Layer

Owing to the limited reserves of fossil fuel and their rapid consumption in the contemporary age, human being is placed on a energy crisis footing. Therefore, it is extremely important to develop renewable energy sources. As one of the emerging renewable energy sources, the solar energy has attracted extensive attention because it is clean, widespread, silent and inexhaustible. Among all sorts of solar cells, polymer solar cells(PSCs) have some unique advantages, such as light- weighted, flexible, ease of fabrication and low–cost. Thus, polymer solar cells may potentially find practical applications in the near future and may b e on the track of mass production. To date, the efficiency of the solution-processed PSCs have exceeded 10%, but further improvement is needed for commercialization.In this thesis, the degree candidate focus on the optimization of the anode buffer layer for high performance device. Previously, PEDO T:PSS has been widely employed as anode buffer layer for PSCs owing to its good film- forming properties, high electrical conductivity and high optical transmittance in visible spectra. However, PEDO T:PSS has strong hygroscopicity and is a naturally acidic substance, thus may lead to deterioration in the ITO substrate. As a result, the overall performance of the device, especially the device stability will be severely damage upon the use of PEDOT;PSS. To overcome this problem, here we choose thin layer of tungsten oxide as the anode buffer layer, owing to their unique optoelectrionic properties. The structure of the device reported in this thesis is ITO/WOX/PCDTBT: PC70BM/PFN/Al, and will be discussed in detailed later. The these is organized as follow:First, we compare the influence of different concentration of the precursor isopropyl alcohol tungsten, the different hydrolysis temperature and the duration of plasma treatment on the device performance, aiming at the optimized film fabrication condition. On the basis of the resulted WOX film, we achieved a power conversion efficiency(PC E) of 5.04%, which is close to the standard device based on PEDOT:PSS(5.58%).In order to further achieving higher performance, we mixed the isopropyl-alcohol tungsten oxide with the PEDOT:PSS in blend ratio of 1:5, and used the blend to spin cast anode buffer layer for PSCs. The obtained PCE is 5.63%, which is slightly higher than that of the control device. The device showed good s helf lifetime with minor PCE degradation of 20% when exposed in air for 44 days, while the control device showed more rapid degradation of 40% as store in the same condition. It is worthy to mention, the device using pristine tungsten oxide as the anode modification showed even better device stability, in which a drop of 12% in PC E was found.Moreover, we found that the device performance can be further enhanced when a thin layer of tungsten oxide was incorporated between the PEDO T:PSS/ WOX blend film and the ITO substrate. Under the standard AM 1.5G illumination, the resulted device show a PC E of 5.93%(VOC=0.93 V, JSC=10.3m A/cm2, and FF=61.5%), which is superior as compared to the device with PEDOT:PSS as the buffer layer. After 44 days, the PCE of the device with the double hole transport layer decrease by 14%, suggesting a more stable lifetime as compared with the common devices.