利用電子傳輸層表面改質提升鈣鈦礦太陽能元件效能

Abstract

鈣鈦礦太陽電池在短短十年間快速發展將光電轉換效率提升至20%以上。其卓越的優點包含在可見光波段裡具有良好吸收率、微米等級的載子擴散距離，和透過結構離子的更換即可擁有不同大小之能階變化等，可看出其為一極具潛力的太陽能轉換材料。然而，為了提高元件載子傳輸效能，如何藉由其他層材料的輔助，提高汲取載子之能力是為現今重要研究內容之一。 首先，鈣鈦礦混合路易士鹼添加劑在傳統氧化鈦傳輸層太陽能元件中，被證明可有效提升電池轉換效率，因此本實驗選用尿素成功降低鈣鈦礦吸光層中的缺陷，並提升元件效率。然而，經由文獻回顧得知氧化鋅和氧化錫具有較高的電子遷移率及更適合之能帶結構，所以被視為可取代氧化鈦之電子傳輸層，但在後續表面形貌、X光繞射和載子汲取效率分析可知氧化鋅與鈣鈦礦在空氣中相當不穩定，會使材料快速降解。此外，比較三者光穿透率氧化錫為其中最佳，因此選擇此項氧化物作為後續表面改質之電子傳輸層材料。 接著，界面改質材料的引入是為了使鈣鈦礦產生之激子更快速分離為載子，並經由傳輸層導離，本實驗將碳60-吡咯烷三羧酸(CPTA)和[6,6]-苯基-碳61-丁酸甲酯(PCBM)分別披覆於氧化錫表面進行比較。過去PCBM被人們單純運用在鈣鈦礦反式太陽能元件結構中，作為有機電子傳輸層，近期被發現也可用於界面改質，但觀察表面結構、X光繞射和光致螢光分析，發現CPTA擁有更佳的載子傳導效果。進一步以FTIR了解，CPTA是由氫氧官能基和氧化錫中含有氧空缺缺陷之錫原子進行鍵結，也因為此化學鍵效果相對PCBM單純披覆上達到更好的傳輸能力，所以更適合用於界面改質提升太陽能元件之光電轉換效率。

Perovskite solar cells (PSCs) have drawn enormous attention in recent years owing to their high power conversion efficiency over 20%. Some of its exceptional properties such as remarkably high absorption over the visible spectrum, long charge carrier diffusion lengths in the μm range, and tunable band gap by interchanging various structure ions reveal its great potential in solar conversion. Nevertheless, in order to promote carrier transmission efficiency of devices, how to elevate the ability to quench carriers aiding with other material layers’ aiding is an important issue nowadays. In the beginning, perovskite added Louis base is proofed to facilitate power conversion efficiency of perovskite solar cells; therefore, urea is adopted and successfully promotes efficiencies of devices. However, it is confirmed by papers that zinc oxide (ZnO) and tin oxide (SnO2) possess higher electron mobility and more suitable band structure, which are considered to be the replacements of TiO2 ETL. After analyzing surface morphology, X-ray diffraction, and carrier quenching efficiency, it is understood that ZnO coated perovskite is quite unstable and quickly degrades in atmosphere. Besides, tin oxide demonstrates the best transmission rate in three of them, so this metal oxide electron transport material is chose to do the next step of surface modification. The second is introducing the surface modification material to effectively separate excitons into carriers and for them to be quenched by ETL. Here, C60 pyrrolidine tris-acid (CPTA) and [6,6]-phenyl- C61-butyric acid methyl ester (PCBM) are separately passivated on SnO2 for comparison. In the past, PCBM was usually adopted in inverted perovskite solar cell as an organic electron transport layer, and it has been found that it could be used in surface as well modification in recent years. However, surface morphology, X-ray diffraction and photoluminescence (PL) show that CPTA transfers carrier more efficiently. In FTIR data analysis, the further study comprehends that the hydroxyl terminal groups on CPTA are coordinated with oxygen-vacancy-related defects of Sn in SnO2, and chemical bonding with interface modification brings better transfer ability than PCBM with non-bonding passivation on SnO2, forasmuch it is more advisable to be applied in facilitating performance of perovskite solar cells.