大面積有機太陽能電池效率增益技術之研究

Abstract

P3HT/PCBM混摻有機太陽能電池效率會隨著作用面積增大而下降，我們經過旋鍍參數、熱退火參數之最佳化，並利用降低ITO片電阻的方式製作成元件，使其在2cm2、4cm2、8cm2之作用面積下，都能達到超過1%的效率。 此外，我們應用簡易微影術於ITO玻璃基板上製作微米級金屬網的二維週期性結構，以金屬的導電性質優於ITO之構想下，改善電洞在陽極上傳輸，並降低元件的串聯電路，提高其充填因子，進而改善元件的效率。在有金屬網結構的ITO上，元件效率從0.79%提升至1% 。 再者，商業上之太陽能電池多為以串並聯方式製作成太陽能模組，我們利用UV照射的方式，使元件間的吸光高分子產生劣化現象，並增加其阻值，讓元件可視為孤立的狀態，進而有效的將元件串聯起來，提升開路電壓，並保持其短路電流及效率。 最後我們以光學非均向性吸收及X-ray繞射現象分析不同後處理下的P3HT/PCBM薄膜。在未處理、溶劑退火、溶劑退火加熱退火的光學吸收增加主要來自於P3HT的結晶性變好、排列性變佳，及共軛鏈長變長所致，另外，也因P3HT的結晶特性，導致以edge-on的排列方式會優於flat-on的排列，所以在大角度入射之TE光消光係數的上升會大於TM光消光係數上升，而增加光學非均向性吸收，在X-ray的強度增加是由於P3HT的結晶域數量變多。在熱退火後以不同的冷卻速率下，雖然X-ray的繞射強度在這些處理方式之下是沒有太大差異，但於光學的分析上，會有吸收及均向性的改變，其主要原因是P3HT的結晶域數量在不同的冷卻速率下並無太大改變，但是以最慢冷卻方式冷卻，會因為在長時間下仍有熱量的輸入，及P3HT鏈間的PCBM被排開，而讓P3HT有更多的空間可以伸長，增加它的共軛長度，所以在光學的吸收及非均向性上會有增加的現象。

Efficiency of a P3HT/PCBM blend organic solar cell is always decreased as increasing the active area. By the optimization of process parameters, including parameters of spin coating, thermal annealing, and the technique for decreasing sheet resistance of ITO, over 1% device efficiency can be achieved in organic solar cells－with active area of 2cm2, 4cm2 and 8cm2. Conventional lithography is applied for patterning micro-scale two dimensional metal meshes on ITO/glass substrate. Because metal film has a superior conductivity than ITO, the device efficiency is improved by enhancing the hole－transport on anode, reducing series resistance, and increasing the filling factor. The device efficiency increases form 0.79% to 1% on ITO substrate with patterned metal meshes. Moreover, commercial solar cells are typically made to a module by parallel and series connection. We use UV illumination to degenerate the light-absorptive polymers and increase the resistance between the devices. The devices can be seen as isolated status, and therefore we effectively make devices into series connection, increase the open circuit voltage, and maintain the short circuit current and efficiency. Optical absorption, optical anisotropy, and X-ray diffraction are used to analyze P3HT/PCBM films under different post-treatments. The increases of optical absorption for un-treated, solvent annealing and solvent annealing along with thermal annealing samples come from the improvement of P3HT crystallinity, much order alignment of polymer chains and the lengthened conjugate chains. Besides, because of the crystalline property of P3HT, P3HT tends to crystallize in an edge-on form instead of in a flat-on form. Therefore, the extinction coefficient of TE polarized light increase more than TM polarized light does at large incident angles and thus the optical anisotropy increases. And the increase of X-ray diffraction intensity attributes the increase amount of crystalline domain of P3HT. With different cooling rates after thermal annealing, the intensity of X-ray diffraction does not perform obvious difference. However, optical analysis has demonstrated changes in absorption and anisotropy. The main reason is that the amount of crystalline domain of P3HT does not change much under different cooling rates. Nonetheless, during the long duration of slowest cooling rate, the exclusion of PCBM in the interspaces of P3HT chains makes P3HT to extend in a larger space and increases the conjugate length thet results in the increase of optical absorption and anisotropy.