高效能鈣鈦礦太陽能電池縱向化學成分及形貌分析

Abstract

有機-無機混摻鈣鈦礦材料已成功地引入太陽能電池領域中，其作為太陽能電池的吸光層，在近幾年間光電轉換效率迅速的上升，目前有機-無機混摻鈣鈦礦太陽能電池的光電轉換效率最高已達到20%。根據相關研究指出，鈣鈦礦太陽能電池的光電轉換效率和鈣鈦礦薄膜的品質息息相關。本研究利用兩步驟沉積法製備有機-無機混摻鈣鈦礦太陽能電池，藉由調控不同濃度的甲基胺碘前驅溶液和二碘化鉛進行轉化反應，發現甲胺鉛碘的轉化程度受到甲基胺碘前驅溶液的濃度影響，因而設計出三種不同轉化率的鈣鈦礦薄膜，以探討不同反應程度之鈣鈦礦材料的結晶性質、表面形貌、化學成分和鈣鈦礦太陽能電池元件表現之間的關係。透過X光繞射和X光光電子能譜分析，我們說明了在轉化過程中三維的PbI6八面體網路和甲基胺碘陽離子之間的交互作用，此外，我們進一步的利用在不同入射角下的X光繞射分析，觀察鈣鈦礦薄膜在垂直方向上的結晶型態，了解鈣鈦礦薄膜縱向成分分布對於鈣鈦礦太陽能電池之影響，進而提出了完整鈣鈦礦結構的轉化機制。最後，我們首度發現二碘化鉛薄膜在表面的晶面排列方向與薄膜內層的排列方向不同，在薄膜表面晶面傾向單一方向排列，具有方向性；薄膜內層受到二氧化鈦鷹架層影響，晶面排列較無方向性，而且轉化而成的甲胺鉛碘會依序原本二碘化鉛晶面的排列方向生長。

Organic-inorganic hybrid perovskite materials have been successfully applied as light absorbers in photovoltaic cell, which boost rapidly in power conversion efficiency, up to 20%. According to the recent researches, the power conversion efficiency of perovskite solar cell depends on the quality of perovskite film significantly. In this study, we used two-step deposition method to fabricate organic-inorganic hybrid perovskite solar cells. We found that conversion ratios of CH3NH3PbI3 were influenced by controlling various concentration of CH3NH3I precursor solution. Therefore, three perovskite films with different conversion ratios were prepared to discuss the relationship between the crystallinity, morphology, chemical composition of perovskite films and photovoltaic performance of perovskite solar cells, respectively. Interaction between an extended three-dimensional network of PbI6 octahedral and CH3NH3I is demonstrated by XRD and XPS measurement. Moreover, we used XRD analysis at various incidence angles to observe the crystallization of perovskite films in vertical direction, to understand how the composition of perovskite in vertical distribution impacts on perovskite solar cell. Finally, we propose the conversion mechanism of perovskite. In addition, different orientations of crystal planes were first observed between the surface and the interior of PbI2 films. Crystal planes tend to arrange in single orientation on the surface of PbI2 films, while crystal planes in the interior are non-directional due to effect of TiO2 scaffold layer. Furthermore, similar orientations of crystal planes were also observed on the surface and in the interior of converted CH3NH3PbI3. Thus, these findings indicated that CH3NH3PbI3 grow along PbI2.