以陣列型介觀TiO2奈米結構為基礎之鈣鈦礦太陽能電池研究

Abstract

有機-無機混成有機金屬鹵化物鈣鈦礦(perovskite)具有1.5 eV的直接能隙、低激子束縛能、擴散路徑長、寬廣的光學吸收範圍 (400-800 nm)以及高吸光係數等優點，使得鈣鈦礦成為薄膜太陽能電池的最佳吸光材料，而其元件光電轉換效率更高達15 %以上，創造了溶液製程薄膜太陽能電池的新紀元。由於鈣鈦礦具有雙極性的傳導性質，其除了做為太陽能電池主要的光吸收材料之外也可以作為電子或電洞的傳輸層，這個特性使得鈣鈦礦元件結構的設計呈現多樣化的優勢；例如，鈣鈦礦/電洞傳輸層的設計可作為一種p-type電極以利於電洞的注入而產生電荷分離，此時鈣鈦礦作為光吸收層與電子傳輸媒介；相反地，鈣鈦礦/電子傳輸層的設計可作為一種n-type電極而產生有效的電荷分離接面，鈣鈦礦因此可以扮演光吸收層與電洞導體的雙重角色。目前最成功的元件結構為n-type金屬氧化物(TiO2)/鈣鈦礦/電洞傳輸材料(Spiro-OMeTAD)的介觀異質接面或平面異質接面，TiO2層作為鈣鈦礦的骨架(Scaffold)並可傳輸電子，因此多孔性的TiO2材料在電池結構上具有非常重要的地位，在此我們提出這個台韓合作研究計畫「以陣列型介觀TiO2奈米結構為基礎之鈣鈦礦太陽能電池研究」，其目的在結合雙方之技術與資源，利用高分子聚合合成出接枝高分子並作為基材模板，並進一步開發出新穎形貌且具有高孔洞性的介觀無機奈米材料並應用於鈣鈦礦薄膜太陽能電池。這些技術的開發包括了鈣鈦礦晶體的合成與高孔洞性的介觀無機奈米材料的製備、元件的組裝與效能量測、瞬態光電動力學量測與電化學交流阻抗分析、以及能量轉換與電子轉移的基礎研究。本計畫之鈣鈦礦的合成、元件的製備與測試以及相關光譜動力學的研究將在台灣進行，而高分子合成及陣列型具有介觀孔洞且高孔隙率的無機奈米材料則由韓國團隊負責，這個國際合作研究計畫將會有非常豐碩的成果產出。

Organic-inorganic hybrid metal halide perovskites have the advantages of direct band gap of 1.5 eV, low excitonic binding energy, large diffusion length, broad light-absorption region and high absorption coefficient, so that perovskites become the best light harvesting materials with reported power conversion efficiencies exceeding 15 % for the next generation thin-film solar cells based on solution processing reaching a new milestone. The bipolar charge transport feature makes perovskite itself acting as a transporter of electrons or holes after charge separation. For example, the perovskite/HTM layers can be served as a p-type electrode while the perovskite/ETM layers can be served as an n-type electrode to design a suitable device configuration. The most successful n-type perovskite solar cells have a device configuration TiO2/perovskite/spiro-OMeTAD, for which TiO2 layer is served as scaffold for perovskite at the same time as an electron transporting medium. Therefore, mesoporous TiO2 layer plays an important role to affect the device performance for a perovskite solar cell. As a consequence, we propose herein the Taiwan-Korea joint proposal with the title “Perovskite Solar Cells based on Organized Mesoscopic TiO2 Nanostructures”. The goal of this proposal is to combine the resources and the techniques of both sides and to make a big breakthrough on the development of a new type of perovskite solar cells. The approach is to use the polymerization technique to synthesis the graft co-polymers as templates so that organized mesoporous TiO2 films can be produced with high porosity that is suitable for loading sufficient perovskite crystals to enhance the light-harvesting and electron transporting ability of the devices. The development of the techniques in this proposal include synthesis of perovskite crystals, device fabrication and characterization, transient photoelectric decays and electrochemical impedance spectroscopy. Time-resolved spectral experiments will also be carried out in order to understand the fundamental operational principle for this type of solar cells. The YSU team of Korea will be in charge for the development of polymer synthesis and the organized mesoporous TiO2 materials with high porosity and the NCTU team of Taiwan will develop the synthesis of perovskites, devices fabrication, and the corresponding characterizations. We anticipate that a fruitful outcome will result by executing this joint proposal.