Theoretical And Experimental Studies On Polymer Solar Cells

Organic solar cells have shown great promising potential because it is mechanical flexible and durable, and the chemical structure can be easily manipulated. Recently, the power conversion efficiency of organic solar cells worked on P3HT:PCBM has already broken through 8%.Recent researches are concentrating on new materials and structure optimization, so we select P3HT:PCBM to research the effect by thin film thickness and anneal temperature.First, we researched the relationship between the rotation speed and film thickness of P3HT:PCBM, then we fabricated 9 devices with different thickness and the structure of ITO/PEDOT:PSS/P3HT:PCBM(X nm)/Al. And their I-V curves and absorbance spectrum were compared. We also calculate the series resistance and grid resistance. Exciton diffusion length is affected by the film thickness. Through the discussion, we know the power conversion efficiency is the highest while the film thickness is 110nm, exciton diffusion length minus the distance between the interface of exciton dissociation and electrodes is very big. The absorbance spectrum is best while the thickness is 65nm, but the contact area between the D and A is very small. HUMO of P3HT can be changed by annealing, but the variation is decided by the thickness.Second, the structure with ITO/PEDOT:PSS/P3HT:PCBM(110nm)/Al were fabricated. We used different temperatures to anneal the device for 30min, then we compared their I-V curves absorbance spectrum and EQE. Then calculate the series resistance and grid resistance, and compared their parameters including open circuit voltage, density of short-circuit current, series resistance, power conversion efficiency and fill factor. We found while the anneal temperature is 145℃, the device performance best. The power conversion efficiency can be enhanced by post-annealing which improve the morphology of P3HT:P3BM active layer.Besides, there is a lower series resistance and the solar cells based on P3HT:PCBM has a better morphology through a post-annealing at 145℃for 30min.We also found the temperature with structural changing of P3HT is between 115℃and 125℃...