具筆柱狀結構之混合式有機矽太陽能電池

Abstract

混合型異質接面太陽能電池，他是一種結合了無機材料與有機材料的太陽能電池。它利用了無機材料矽所擁有的優異光吸收特性與較高的載子遷移率表現，搭配上有機材料PEDOT:PSS可低溫且全溶液製作的優點，形成的一種製程簡單快速與低發電成本的高轉換效率太陽能電池，有潛力成為下世代的光伏元件。為了滿足降低發電成本與可撓性應用的需求，基板減薄已是不可避免的趨勢。然而我們知道在矽基板減薄的同時，元件表面上光吸收與抗反射能力顯得更為重要，為了使元件效率提升，因此我們將在矽基板表面上蝕刻出奈米結構做為抗反射層，來降低反射率進而增加入光量。此外，表面奈米結構的產生也能夠增加有機材料與矽基板之間的p-n接面面積，使元件能有更大的面積能分離電子電洞對，而有更優異的電流(Jsc)表現。在本論文中，我們研究藉由奈米球微影術及金屬輔助蝕刻形成奈米筆柱狀結構，並有效的利用漸變折射率特性大幅降低矽晶片表面反射率，且將其應用於混合型太陽能電池上。 我們利用銀當作金屬催化層並搭配強弱氧化劑雙氧水與硝酸鐵不同比例的調變，成功蝕刻出具漸變折射率的筆柱狀結構，使其加權反射率降至7.4%，這是由於筆柱型結構透過尖端奈米錐出色的漸變折色率特性最大限度的降低入射光直接反射的損失，同時利用下端奈米柱結構增加有效光吸收路徑，最終使得該結構獲得優異的抗反射效果。同時由於筆柱型結構的錐柱尖頭部分會使有機溶劑PEDOT:PSS覆蓋結構表面積大於奈米柱結構，因此我們可以獲得更多的PN junction面積來分離電子電洞對，進而有效提升短路電流Jsc。 搭配上以原子層沉積方式製作出的超薄氧化矽做為鈍化層，分別在矽晶片的正反面沉積3和15A彌補了表面缺現複合，而元件的光電轉換效率可達13.61%。最後我們希望可以把上述的表面鈍化方式和優異的抗反射結構從625um厚度的矽晶片轉移至150um的薄矽基板，達到基板減薄，減少材料成本的目的，此外我們期望當矽奈米筆柱結構能被PEDOT:PSS完整包覆時，可以搭配上平坦化連續性的正電極覆蓋在結構上，解決元件光性與電性無法兼顧的情況。

Hybrid organic-silicon solar cells, which combine the advantages of both inorganic and organic solar cells, are promising candidates for next-generation photovoltaics due to their low cost, simple fabrication processes and potential for high power conversion efficiency. Nanoscale surface texture is important for Hybrid organic-silicon solar cells in order to enhance optical absorption for thin-silicon substrates, as well as to increase the junction area for collection of charge carriers. In this study, we employee nanosphere lithography and metal assisted chemical etching (MACE) techniques to fabricate pencil-shaped nanorod structures. By using different kinds of oxidants and tuning the relative concentration ratios, we successfully fabricate pencil rod structure which shows a low weighted reflectance of 7.4% due to the graded-refractive-index effect. The reflectance is largely suppressed due to the modulation of the tapered top surface morphology, which helps to elongate the light absorption path. Moreover, the tapered tips of the pencil rods can boost the organic coverage ratio for carrier separation and collection, thereby effectively increasing the short-circuit-current, Jsc. Moreover, by passivating the rear and front nanorod surfaces with an ultra-thin aluminum oxide, 15Å and 3Å respectively, using atomic layer deposition (ALD) technique to produce as a passivation layer on substrate front and back side. B, We successfully boost the open-circuit voltage and achieve a power conversion efficiency (PCE) of 13.61%. We expect that the device performance can be further enhanced by full organic surface coverage on pencil rod structures to benefit from superior optical absorption and carrier collection with the enlarged junction area. Finally, we hope to fabricate pencil rod structure on thin substrates to reduce the material cost.