利用二氧化鈦奈米桿改善鈣鈦礦晶體薄膜增益太陽能電池效率

Abstract

近來有機-無機鈣鈦礦太陽能電池領域蓬勃發展、備受矚目，由於其極高吸收系數與極佳的光電轉換效率，因此能降低太陽能電池薄膜厚度並達到極佳之太陽能元件效率。 目前，已有各種鈣鈦礦太陽能電池結構被發展，許多電子傳輸層與電洞傳輸層也相繼被替換，不過高效率結構主體仍以高溫燒結之二氧化太光陽極並沉積甲胺鉛碘(CH3NH3PbI3)作吸光層為主。然而，這種結構由於二氧化鈦層需要極高的燒結溫度(~500oC)，因此將會提高元件製作成本與複雜度，若將二氧化鈦層移除，發展平面異質接面結構，礙於CH3NH3PbI3本身擴散長度(~100nm)之限制與溶液沉積法所得之鈣鈦礦晶體表面形貌不佳，造成目前元件效率無法提升。 本論文利用合成出低溫之二氧化鈦奈米桿，藉由添加入CH3NH3PbI3系統內，我們發現二氧化鈦在系統內可幫助載子分離、並且當二碘化鉛與甲胺碘反應後，鈣鈦礦晶體表面的形貌改善，使得晶體彼此聯結性增加，這些原因有助於元件效率的提升，並且在此製程裡我們成功製作出一種新型態，簡單、低溫、低成本之混摻(Hybrid)結構有機-無機鈣鈦礦太陽能電池，並成功將元件效率提升至8%。

Inorganic-organic perovskite solar cells are significant technology, promising cost-competitive solar power by cheap material and fabrication costs as compared to established conventional silicon solar cell. Mesoscopic structure heterojunction solar cell showed higher efficiency devices than other kinds of structure solar cells. But, they have serious drawback such as needed high annealing temperature for forming well crystalized TiO2, which makes more complicate process of fabrication and flexible less substrates. To overcome this, researchers move to planar heterojunction perovskite solar cells. However, they also have the problems of limited diffusion length and morphology hard to control by using solution processed deposition. The morphology is wisely controlled by varying processing conditions, and demonstrated that the highest photocurrents achievable only with the highest perovskite surface exposures. Here, we effectively synthesized well-crystalline TiO2 nanorod by low temperature sol gel process, followed by ligand exchange method by using acrylic acid. In order to fabricate the perovskite film, we also synthesized CH3NH3I to gain the high purity powder, which was impregnated with TiO2 nanorod for fabrication of a new structure that is hybrid heterojunction perovskite solar cell system. With improved solution based film formation shows higher efficiency of Jsc(Short-circuit current) and better FF(Fill factor). It may be due to the TiO2 nanorod provides more interfaces for the carrier charge separation and morphological changes of PbI2 in TiO2 nanorod such as pin-holes. Further, improved the morphology of perovskite surface occurred by the formation of better connection surface of perovskite crystalline because of more nucleation spots available on CH3NH3I for react with PbI2. Under optimized condition, the efficiency of device was raised to 8% which is better than other solution process planar-heterojunciton solar cell.