藉溶液法及真空鍍膜技術製成多元高豐度元素(碳、銅、鋅、錫、硫、硒)光電元件之探討

Optoelectronic Devices Based on Earth Abundant Element (C, Cu, Zn, Sn, S, Se) by Solution and Vacuum Processes

陳韋兆(Wei-Chao Chen)

指導教授 ： 李志浩 ； 陳貴賢 ； 林麗瓊

國立清華大學/原子科學院/工程與系統科學系/博士(2016年)

摘要

本論文主要在探討使用地球多豐的元素合成光電材料及元件，並且探討其製程與機制。首先，我們發展三種硫硒族化合物的針對薄膜太陽能元件製成，包含銅鋅錫硫奈米粒子、多重硒化法、以及快速升溫燒結法。在微波輔助合成法中，我們利用油胺（ OLA）和三辛基氧化膦（ TOPO ）作為反應溶劑。用兩個互補的溶劑做出適當的比例，這種微波加熱的方法能夠縮短從200分鐘至10分鐘的反應時間得到高品質銅鋅錫硫的奈米粒子。我們的研究結果證明，適當的化學計量和合理的能帶隙（〜 1.5 eV）的結晶銅鋅錫硫奈米粒子是可以實現的。同時，我們還提出了多層金屬疊體製備的多重硒化法製作銅鋅錫硒薄膜。通過在多重硒化過程，成核溫度可以精確地從150度到500度被控制，經由精確的控制成核溫度，高均勻性和高晶體品質性的銅鋅錫硒薄膜可以準確地被得到，且可以完全排除二次相。最後，經由精確的控制燒結溫度銅鋅錫硒薄膜太陽能電池的元件效率可以達到 5.8%。在第三部分，我們使用多堆積的金屬層以及快速升溫燒結法合成高品質的銅鋅錫硫硒薄膜。我們發現，製備金屬疊層前驅物時，沉積層數和疊層金屬相互擴散問題對薄膜和元件效率有顯著效果。與傳統的3層堆前驅物的元件比較，使用修飾後的9層疊體前驅物在快速升溫燒結法處理的元件效率可從4.8提高到7.7 ％，且可合成晶體密度高，化學當量比適合，並抑制富銅的雙層結構形成。
最後，我們介紹了使用單壁奈米碳管通過超聲霧化的新方法製成具有高透明，高導電性，大面積的導電薄膜。由於個別的奈米碳管內的強凡德瓦力，溶解單壁碳奈米管是一個極具有挑戰性的工作;因此，為了促使在溶劑中的奈米碳管溶解，我們使用導電高分子修飾奈米碳管表面。經過控制導電高分子的側鍊長短作我們發現，無定形碳，和良好分散的奈米碳管可以完美的進行分離。最後，使用較長側鍊的導電高分子分散的奈米碳管的溶液經由超聲波噴霧，精確量將要溶液均勻地沉積到大面積的玻璃基板上，形成超高平整，
ii
高透射，和高導電性的透明導電膜。我們希望，由於其近紅外透射特性和優良的電傳輸特性奈米碳管的薄膜將是多層結構太陽能電池，薄膜太陽能電池以及熱電元件，以及其它需要p型透明導體的應用中最適合的材料。

關鍵字

薄膜太陽能電池 ； 透明導電電極 ； 奈米碳管 ； 硫硒化合物

並列摘要

This dissertation presents investigations of the design and synthesis of optoelectronic materials with earth abundant element as well as novel experimental design methodologies. First, we developed three different processes to synthesize quaternary chalcogenide compound for solar cell application, including CZTS colloidal nanoparticles (NPs) by microwave assisted heating process, multi-step selenization process, and fast ramping annealing processes. In microwave heating process, we utilize oleylamine (OLA) and trioctylphosphine oxide (TOPO) as the reaction solvents. With appropriate ratio of two complementary solvents, this microwave heating method can shorten the reaction time from 200 min to 10 min with high quality of CZTS NPs. Our results proved that the crystalline CZTS NPs with appropriate stoichiometry and reasonable energy band gap (~1.5 eV) could be achieved.
Meanwhile, we also proposed a multi-step selenization process for the Cu-Zn/Sn metallic stacked precursor to prepare Cu2ZnSnSe4 (CZTSe) absorber. Then the reaction in fixed Se vapour pressure in a series of increasing temperatures was studied. By precisely controlling the nucleation temperatures from 150 oC to 500 oC during 4-step selenization, the homogeneity and crystal quality of CZTSe can be achieved, and the binary phase can be totally ruled out. Finally, stoichiometry with less impurity CZTSe thin film formed at the optimum annealing conditions 500 oC for 10 min: lower or higher temperature lead to insufficient crystallization or undesirable phase segregation. A device efficiency of 5.8 % for the CZTSe solar cell have been achieved with an open circuit voltage of 370 mV, short circuit current of 31.99 mA/cm2, and a fill factor of 48.3%.
In the third part, we synthesized high quality CZTSSe with fast ramping heating process with multi-stacking metallic layers. We demonstrated that precursor deposition numbers and inter-diffusion issue have a significant effect on the quality of thin film and device performance. The device prepared with conventional 3 layers stacked, with excessive Cu-rich secondary phase
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formation at the back contact region, results in poor performance of devices due to the poor interdiffusion of precursors. By using the modified 9 layer stacked precursor and fast ramping heating process the device efficiency can be improved from 4.8 to 7.7% with open circuit voltage enhancement from 0.44V to 0.5V due to a compact, smooth microstructure, and the suppression of Cu-rich bi-layer formation.
Finally, we introduced a new method to fabricate SWNTs network films with high transparent, high electrical conductivity, and uniform in large (10 cm*10 cm) scale by ultrasonic spray. Due to van der Waals' force within individual SWNTs, dispersion of SWNTs in solvent is a challenging issue; therefore, in order to facilitate SWNTs dissolution in solvent, we functionalize surface of SNWTs with conductive polymer. As SWNTs dissolved, we centrifuged the solution, making the bundle SWNTs, amorphous carbon, and well-dispersed SWNTs to be separated. Finally, dispersive SWNTs solution is ultrasonically sprayed, permitting accurate quantity of SWNTs to be deposited onto substrate with large area uniformity, forming ultra-high smoother, high transmission, and high conductivity transparent conductive film. Hopefully, the optical and electrical transport properties of the SWNTs will be appropriate candidate for multiple-junction solar cells, thermo-photovoltaics, and other applications benefiting from a p-type transparent conductor application due to high near-infrared transmission.

並列關鍵字

Thin film solar cell ； transparent conducting film ； carbon nanotubes ； sulfide/selenide compound

參考文獻

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