The Performance Improvement Of Polymer Solar Cells With Solution-processed Electrode Modification Layer

This dissertation focuses on the performance improvement of polymer solar cells (PSCs) based on solution processed electrode modification. There are three major parts: the anode modification of polymer solar cells with large-sized Ag nano-particles (Nps) incorporated into PEDOTPSS layer; the modified cathode surface via micro-nano structure induced by solution process; simultaneous anode and cathode modification with polyethylene glycol (PEG). The main results are shown as follows:1. Effect of the Ag nanoparticles incorporated into PEDOT:PSS layer on the performance of polymer solar cells.Ag Nps with the size of about40nm and80nm were incorporated into PEDOT:PSS anode buffer layer of polymer solar cells, respectively. Improved short-circuit current density and power conversion efficiency (PCE) were obtained with appropriate doping ratio in both cases. It is founded that the rough interface of PEDOT:PSS layer incorporated with large-sized Ag Nps increases the contact interface between the anode and the photoactive layer, and provides relatively shorter routes for holes to travel to the anode, enhancing the hole collection efficiency of the anode. The improved conductivity of PEDOT:PSS can also benefit the charge collection efficiency of the anode. Besides, the oversized Ag Nps of the PEDOT:PSS layer protrude into the active layer and destroy the contact of active layer and PEDOT:PSS layer, leading to leakage current and deteriorated efficiency of PSCs.2. Influence of Micro-nano structure cathode surface on the performance of polymer solar cells.With the aid of solvent ultrasonic processing and thermal-annealing,the surface of the active layer appears rough and uneven structure by introducing PGMEA (propylene glycol mono-methyl ether acetate) into the P3HT:PCBM active layer. Therefore, the Al electrode surface on the upper of the resulting active layer shows the complementary rugged micro-nano structure. The effects of PGMEA volume ratio, solvent ultrasonic time and annealing process on the performance of PSCs are investigated, and it is founded that the optimized PCE is achieved when the PGMEA volume ratio is2%, the solvent ultrasonic time is15min, and the post thermal-annealing time is50min. The current density-voltage characteristic, the external quantum efficiency, the ultraviolet visible absorption spectroscopy, and the AFM morphology show that the cathode with the micro-nano structure surface increases the interface of active layer and Al electrode, and then shortens the transmission path of charge carriers and increases the charge collection efficiency of Al electrode. Besides these advantages, the micro-nano structure surface of the cathode reflects the incident light and improves the absorption of the active layer, which can also improve the efficiency of PSCs.3. Demonstration of the simultaneous anode and cathode modifications with PEG of the polymer solar cellsBy introducing PEG into the PEDOT:PSS anode buffer layer, the conductivity of PEDOT:PSS film increases and the hole collection efficiency of the anode improves. PEG could migrate upward to the active layer/Al interface and form a cathode buffer layer to improve the performance of PSCs when PEG is doped into the P3HT:PCBM active layer. Based on the above results, we deposited a PEG layer on the surface of PEDOT:PSS layer, and found that PEG can not only penetrate downward into the PEDOT:PSS layer to improve the conductivity of the anode buffer layer, but also migrate upward through the whole active layer to the active layer/Al interface, improve the interface contact of active layer/Al electrode as a cathode buffer layer. The formed bi-functional PEG layer improves the PCE of polymer solar cell obviously.