以氧化石墨烯及還原氧化石墨烯衍生物為電極之反式平面鈣鈦礦太陽能電池

Abstract

本論文主要氧化石墨烯(GO)為基礎，作為電洞傳輸材料，以三明治結構，依序沉積電洞傳輸層、鈣鈦礦吸光層、電子傳輸層於ITO導電玻璃上，最後蒸鍍銀電極，製備正型平板鈣鈦礦太陽能電池，其光轉換效率為13.8%。但由於含氧官能團的引入，破壞了石墨烯的大π共軛結構，氧化石墨烯具有絕緣的特質，使其導電性和其他性能顯著降低，因此我們利用三種不同還原劑，分別為聯胺、硼氫化鈉以及4-肼基苯磺酸，製備還原氧化石墨烯(rGO)，試圖恢復其材料的導電性，成功提升其光電流，光轉換效率分別為16.0%、15.3%以及16.4%。此外，我們用的材料皆是低溫製程，因此還可以製作在可撓式基板，其rGO的效率可高可達13.8%，而GO光轉換效率也將近9%。 另外以PEEDOT:PSS為電洞傳輸與rGO比對，做元件穩定性測試，PEEDOT:PSS在650小時左右，元件已失去效率，而rGO在1000小時候尚有50%以上的效率。rGO材料不僅穩定性提升，在製備上較簡單、成本低，也具有好的載子傳輸特性，但隨著使用不同的還原劑，其還原劑的強弱不同之外，還原劑添加的劑量，皆會影響rGO在導電玻璃ITO上的覆蓋率，故其成膜性將是一個非常重要的議題。

Graphene oxide (GO) and its derivatives as the promising hole-extracting layer (HEL) are used for inverted planar heterojunction (PHJ) perovskite solar cells(PSC). The effect of GO reduction conditions on hole extraction properties is studied. We synthesized reduced graphene oxides (rGO) of three types – rGO-NH, rGO-BH, rGO-HBS – via reduction of GO with reducing agents – hydrazine, sodium borohydride and 4-hydrazino- benzene sulfonic acid – as HEL. The devices fabricated by reduced graphene oxides show the higher photovoltaic performance attaining power conversion efficiency (PCE) 16.0 %, 16.4 % and 15.3 under AM 1.5 G one-sun irradiation , which is superior than GO with PCE 13.8%. Moreover, the flexible solar cell based on rGO shows high PCE of 13.8% and this device is robust against bending and can maintain its efficiency under bending situation. Based on the controlled experiment, it was found that the trap states on GO and rGOs play a significant role. The lower performance of GO is related to its insulating properties of nanosheets. Film formation and coverage of the substrate by graphene nanosheets as the determinant factor was realized.