Studies of the effects of annealing and interface modification on the performance of polymer photovoltaic devices
|關鍵字:||高分子;太陽能電池;光伏元件;polymer;solar cells;photovoltaics;microwave annealing|
|摘要:||隨著能源問題的日益嚴重，太陽能電池的研究更是如火如荼的發展，近年來高分子太陽能電池之光電轉換效率已達5%，主要是利用P3HT/PCBM [poly(3-hexylthiophene) / [6,6]-phenyl C61-butyric acid methyl ester]等這類有機材料所形成的p-n結構所製作而成，由於這類有機太陽能電池具有成本低、重量輕、具可撓性及容易製造大面積元件等優勢，研究提升製程速度和效率便可使太陽能電池的價格和效能更具競爭力。
The power conversion efficiency of organic photovoltaic devices up to ~5% has been achieved recently by creating organic p-n bulk-heterojunction, such as that of p-type poly(3-hexylthiophene) (P3HT) and n-type [6,6]-phenyl C61-butyric acid methyl ester (PCBM), in the active layer. Because of the advantages, such as low-cost, light-weight, flexible and large area fabrication capability, developing high throughput and efficiency methods are thus essential to enable the photovoltaic system more competitive in price and performance. Solvent annealing is one of the candidates to improve the efficiency of solar cells. For investigating the effect of solvent annealing on the performance of polymer solar cells, we studied two important parameters such as the composition ratio and solvent evaporation by several measurements and morphology characterizations. The optimized composition ratio of P3HT/PCBM was 1 to 1 from light J-V curves and EQE value. When the concentration of PCBM increases, the light absorption and crystallinity of P3HT were reduced. The confocal laser scanning microscopy (CLSM) shows that the uniform and large amounts of interface area were obtained while ratio is equal to one. As a result, the moderate quantity of PCBM can effectively create exciton dissociation cites, to produce free electrons and holes and improve the performance of polymer solar cells. As for the influence of solvent evaporation, the crystallinity and light absorption was improved in longer drying time. In addition, red-shift of vibration peaks indicates the conjugated polymer chain has closed packing structure. From the optical sitmulation, the higher absorption in the active layer was resulted from optimized index-matching to form grading structure in the multi-layer device architecture. To increase the fabrication throughput, we demonstrated a microwave annealing method to treat the polymer devices and found that it will increase the performance of the photovoltaic cells. The microwave irradiation will selectively heat the active layer and cathode and reduce energy loss in the ITO substrate. The metal cathode heat by microwave is due to the thickness which is lower than the penetration depth of microwave. Finally, the optimized efficiency of polymer solar cells can be improved to 3.6% in only 1.5 min. The microwave is an efficient way to improve the performance of the photovoltaic device. To pursue higher power conversion efficiency in polymer PV, highly conductive PEDOT:PSS was used to reduce the series resistance in equivalent circuit of the polymer solar cells When the mannitol doped in the PEDOT:PSS, the conductivity was 40 fold improvement compared to the pristine device. The power conversion efficiency was improved and series resistance was reduced as mannitol concentration increased. Comparing with the pristine PEDOT:PSS,. Thus, the short circuit current increased from 12 to 14.7 mA/cm2. Finally, the optimized power conversion of polymer solar cell was 5.2% with 60mg/mL manntiol doping.