Study On The Morphology And The Interface Modification Of Polymer Solar Cells

ABSTRACT:This thesis investigates the factors that influence the efficiency of the heterojunction polymer solar cells, and it includes three studies. Firstly, the layer-evolved heterojuntion polymer solar cell was fabricated using the orthogonal solvents, and the formation process of the heterojunction structure was investigated. The effect of preparation technique on the morphology of P3HT:PC6iBM film and the performance of the device were also studied. Secondly, the work function of ITO was tuned by plasma treatment, and the inverted solar cell without electron transport layer was fabricated. Finally, we applied the low-temperature atom layer deposited ZnO and Al2O3films to the inverted polymer solar cell fabrication. And the effect of the films on the electron collection was studied.1. The layer-evolved heterojunction films were fabricated using the orthogonal solvents. The film formation process and the effect of annealing on the morphology and the performance of the devices were investigated.(?) DCM could decrease the chain packing and the crystallinity of the P3HT film by the swelling effect. DCM also assists in the penetration of the PCBM into the P3HT underlayer during spin-coating. After the DCM evaporates, the PCBM in the P3HT matrix hinders the self-reorganization of P3HT, causing a drop in the absorption intensity of P3HT.(?) The changes of the structural properties and the composition distribution of the annealed composite films were investigated. The results indicate that the crystallization of P3HT in the LBHJ film is enhanced during annealing. The ordered P3HT facilitates the charge transport. The PCBM molecules diffuse into the P3HT matrix vertically and laterally during annealing process, which leads to an improved interpenetrating donor-acceptor network. Thus, the device efficiency reaches2.83%after annealing at110°C for10min.(?) Post-annealing deteriorates the performance of LBHJ devices significantly. The deterioration of post-annealed LBHJ solar cells is mainly attributed to the nucleation and growth of PCBM crystals at the active layer/Al interface, which harms the contact between the Al electrode and the active layer and leads to the barrier for charge transport.2. The work function of ITO was tuned by plasma treatment, and the inverted solar cell with the plasma-treated ITO was fabricated.(?) The work function of ITO decreases after Ar and H2plasma treatment. The plasma treatment has no significant influence in the morphology, the surface energy and the transmittance rate of the ITO film.(?) The inverted solar cell without electron transport layer was fabricated using plasma-treated ITO. The performances of the devices with P3HT:PCBM and PBDTTT-C:PCBM system achieved3.57%and6.3%, respectively. The improved performance is attributed to the increase of built-in potential across active layer and the better energy match between ITO work function and LUMO of PCBM.(?) The shift of the ITO work function has the good air stability. The inverted solar cell with plasma-treated ITO is stable in dark, while it is a little less photo-stable than the device with ZnO interlayer.3. The ZnO and Al2O3films were fabricated using atom layer deposition. And the films were applied to the inverted solar cells as the electron transport layers.(?) The dense and pinhole-free ZnO films were deposited at various temperatures (60°C-190°C). The deposition temperature has significant influence on the morphology and the preferred orientation of the ZnO film. While the devices with the ZnO films deposited under different temperatures achieve the similar power conversion efficiency.(?) The device with ultrathin Al2O3layer has the low fill factor and open voltage. And the J-V curve shows an S-shaped kink. The kink was eliminated after light-soaking. The improvement of the performance after light-soaking is mainly attributed to the decrease of the ITO work function and the improved conductivity of the Al2O3film.