Performance Optimazation Of Organic Solar Cells

Organic solar cell (OPV) has been considered as a supplement to inorganic solar cells for its advantages, including low cost, light weight, flexibility, diverse processing methods and compatible to large-scale manufacturing, and has become a hot topic in academic research. Remarkable progress has been made in the last few years, both in material synthesis and device structure designing. The main object of this thesis is to understand the device structure-performance relationship by varying the cathode buffer layer, donor and accepter materials, processing procedures and additional pheotosensitizing layer, and with that to improve the device performance.1. The P3HT:PC61BM based bulk heterojunction solar cell was optimized by varying the thickness of P3HT:PC61BM film and thermal annealing process. Results suggest that the optimal P3HT:PC61BM film thickness is240nm and the annealing temperature is120℃. Under this condition, the highest power conversion efficiency of3.12%can be reached. Two kinds of ZnO nanoparticles with different sizes of6-8nm and100-500nm were synthesized by sol-gel methods. The ZnO nanoparticles were used as the cathode buffer layer in P3HT:PC61BM solar cell, and the device performances were studied and compared. Results indicated that ZnO with smaller particle size is more suitable for use in organic solar cell. Meanwhile, ZnO nanoparticle as cathode buffer layer can greatly improve the thermal and in-air stability of the device.2. The P3HT:ICBA based solar cell was optimized with P3HT:ICBA layer thickness of240nm and post thermal annealing at120℃to reach efficiency of 3.08%. By using chlorobenzene (CB) as solvent and1,8-diiodoperfluorooctane (DIO) as additive, the P3HT:ICBA based device was further optimized. To make device with ZnO as cathode buffer layer, vacum drying processes was developed and applied to dry the photoactive layer. High power conversion efficiency of4.43%was achieved by using vacuum dry technique and ZnO as cathode buffer layer. Stability investigations on P3HT:PC61BM and P3HT:ICBA devices showed that P3HT:PC61BM based device is more stable than P3HT:ICBA based one.3. Using a new donor material PBDT-TT-F, the optimized BHJ solar cell based on PBDT-TT-F:PC61BM can reach high efficiency of5.37%. External quantum efficiency of the PBDT-TT-F:PC61BM device showed that this device has low photon to current conversion efficiency in the wavelength between350-550nm for the low light absorbance of PBDT-TT-F. In contrast, P3HT have an intensive absorption band from450nm to600nm. A new device structure was then proposed, in which P3HT was utilized as photosensitizing layer for PBDT-TT-F:PC6)BM device. With the optimized P3HT thickness of20nm, PBDT-TT-F:PC61BM based device showed improved spectral response in the wavelength range of400-600nm, and consequently increase the short-circuit current from11.42mA/cm to12.15mA/cm.