矽/有機混成太陽能電池與以金屬為主動層之太陽能電池

Abstract

本論文旨在研究矽奈米結構/有機混成太陽能電池和以金屬為主動層之太陽能電池。矽/有機混成太陽能電池的原理述於第一章第四節，其研究詳情則述於第二章和第三章。在第二章中，我們比較矽奈米線陣列和矽奈米洞陣列的形貌差異，包括長度（深度）、密度、奈米結構中空氣所佔比例。其後，形貌差異所導致的光學特性也有所探討。我們發現在相似的長度或深度時，矽奈米洞陣列較矽奈米線陣列有較低的反射率，而且矽奈米洞有較佳的光子侷限效應。再者，高密度之矽奈米洞陣列有較多的界面面積。因此，矽奈米洞/聚(3,4-乙烯基二氧吩):聚(苯乙烯磺酸鹽) （PEDOT:PSS）混成太陽能電池有較佳的元件表現，其短路電流密度（Jsc）為35.36毫安培/平方公分、開路電壓（Voc）為0.510伏特、填充因子（FF）為62.36%、光電轉換效率（PCE）為11.25%。 在第三章中，我們開發了化學拋光式蝕刻（CPE）和低壓輔助被覆法（LPAC）來解決矽奈米結構和PEDOT:PSS之間的載子複合以及有機材料在奈米結構上被覆不完整的狀況。在經過CPE的修飾之後，矽奈米洞陣列變成矽奈米針尖，而且它仍然有廣域的光子捕捉特性。結果顯示，等效的少數載子生命期和PEDOT:PSS在奈米結構上的被覆情形均有明顯的改善。最後，矽奈米針尖的混成太陽能電池的表現更進一步，其FF高達70.94%、Jsc為35.36毫安培/平方公分、Voc為0.528伏特、PCE為13.36%。 在金屬太陽能電池方面，由於以往以金屬為本的熱載子光偵測器已有所發展，我們便嘗試利用金屬來作為光主動材料來製作太陽能電池。熱載子效應方面，除了以往的載子衰減延遲和能量選擇層，我們發現一個新的方法來抽取光生熱載子，此即主動層厚度限制法，本法是基於熱載子生命期和電子—（聲學）聲子的平均自由路徑的概念。經多重因素考量下，本研究的主動層的選擇為黃金，因為他的平均自由路徑較長，且化學活性極低。元件的結構有兩種，包括染料敏化太陽能電池（DSSC）結構和三明治結構。結果顯示，DSSC結構的元件無法發揮效果，因為黃金會與電解液（I-/I3-）反應。更甚者，幾乎所有的金屬皆會與其反應。三明治結構方面，我們嘗試了PEDOT:PSS/聚(3-己烷基噻吩)（P3HT）/黃金（20奈米）/[6.6]-苯基-C61-丁酸甲酯（PC60BM）、氧化鋅/PC60BM/黃金（20奈米）/金屬氧化物（氧化釩（V）、氧化銅、氧化鎳）或2,2',7,7'-四[N,N-二(4-甲氧基苯基)氨基]-9,9'-螺二芴（Spiro-OMeTAD）/PEDOT:PSS、n型氮化鎵/PC60BM/PFN/黃金(5奈米)/氧化釩（V）/P3HT，等數種元件。結果顯示，僅有最後一種有光伏效應，其平均Jsc、Voc、PCE、FF分別是10.00微安培/平方公分、0.9540伏特、0.0020503%、21.520%。

In this dissertation, the research includes Si nanostructure/organic hybrid solar cells and the solar cells with metal as active layers. The principle of Si/organic hybrid solar cells is described in chapter 1 (section 1.4), and the research detail of Si nanostructure/organic hybrid solar cells are described in chapters 2 and 3. In chapter 2, we compare the morphology difference of silicon nanowire (SiNW) arrays and silicon nanohole (SiNH) arrays. The length (or depth), density, and air-filling fraction of both SiNW and SiNH arrays are investigated. The morphology induced different optical properties are also measured and analyzed. We found that SiNH arrays have lower reflectance than that of SiNW arrays with similar length; also, SiNH arrays have better optical trapping effect as compared to SiNW arrays. In addition, high density SiNHs can form more junction area. Therefore, SiNH/poly(3,4-ethylenedioxythiophene): poly(styrene sulfonate) (PEDOT:PSS) hybrid solar cells have the best performance with a short-circuit current density (Jsc) of 35.36 mA/cm2, open-voltage (Voc) of 0.510 V, fill factor (FF) of 62.36%, and power conversion efficiency (PCE) of 11.25%. In chapter 3, we developed chemical polishing etching (CPE) and low-pressure-assisted coating (LPAC) method to solve the problem of carrier recombination at the junction between Si nanostructures and PEDOT:PSS, and the incomplete coverage of organic materials on nanostructures. After CPE modification, SiNH arrays become silicon nanotips (SiNTs), which also have broadband light-trapping characteristics. As a result, the effective minority-carrier lifetime and the coverage of PEDOT:PSS on the surface of nanostructures are enhanced. Finally, hybrid solar cells fabricated with surface-modified SiNT arrays exhibit a high FF of 70.94%, Jsc of 35.36 mA/cm2, Voc of 0.528 V, and PCE of 13.36%. Regarding metal-based solar cells, previously, metal-based hot-carrier photodetector with hot-carrier effect was developed. Therefore, here, we try to use metal as photo-active material for solar cells. Rather than the conventional carrier relaxation retardation and energy selective contacts, we discovered a new method to extract photo-generated hot carriers, that is, active layer thickness limiting, which is based on the concept of hot-carrier lifetime and electron-(acoustic) phonon mean free path. Au was chosen as active layer due to its long mean free path and weak chemical actively. The devices were fabricated in dye-sensitized solar cell (DSSC) configuration and sandwich configuration. As a result, DSSC configuration devices are not workable because Au can react with electrolyte (I-/I3-). Also, almost all of metals can react with it. Regarding sandwich configuration, we tried PEDOT:PSS/P3HT/Au (20 nm)/PC60BM, ZnO/PC60BM/Au (20 nm)/metal oxide (V2O5, CuOx, NiO) or Spiro-OMeTAD/PEDOT:PSS, and n-GaN/PC60BM/PFN/Au (5 nm)/V2O5/P3HT devices. Only the last one has photovoltaic effect. The average Jsc, Voc, PCE, and FF are 10.00 μA/cm2, 0.9540 V, 0.0020503%, and 21.520%, respectively.