- 學位論文
V-VI, I-III-VI2, I2-II-IV-VI4硫族化合物半導體材料電化學合成
Electrochemical Syntheses of V-VI, I-III-VI2, I2-II-IV-VI4 Chalcogenide Semiconductors
摘要
電化學研究化學物質在電子轉移過程中，其電化學反應與反應電位的關係，因此，穩定且僅作為電子傳遞功用的熱裂解石墨和白金電極為常見電化學研究中的電極選擇。然而在大部份實際情況的電子轉移過程中，電極材料會與電解質中的化學物質相互作用反應。在本研究中，我們探討包含五六族碲化鉍、一三六族銅銦鎵硒及一二四六族銅鋅錫硫等三種硫族化合物半導體材料的電化學研究，並從中發展出四種技術簡述如下: (i) 我們利用單步驟電化學蝕刻在碲化鉍塊材表面蝕刻出碲化鉍奈米片狀陣列結構，施加電壓的大小和時間可以控制碲化鉍奈米片狀陣列結構的間距和深度，分析碲化鉍奈米片狀的結果顯示為單晶的碲化鉍，平均厚度和電阻率為399.8 奈米和137.34 微歐姆⋅公尺。我們也提出了碲化鉍奈米片狀陣列結構的成長機制，並應用於量子點敏化太陽能電池，有著1.12%能源轉換效率表現。 (ii) 我們提出氣相-固相轉變生長機制且無介面活性劑輔助的合成方法合成碲奈米線，此單步驟電化學合成法在室溫下進行反應，合成出的碲奈米線沿著[001]的方向成長，平均直徑小於20奈米。此碲奈米線有著表面增顯拉曼散射效果，並在吸收光譜中於350-750奈米波長區間有吸收峰、螢光光譜中於400-700奈米波長區間有發射峰，可被直接應用當成p型摻雜劑於石墨烯電晶體上，也可作為超電容中的電極端應用。 (iii) 我們利用電化學方法進行銅銦鎵硒表面鈍化作用，使得銅銦鎵硒表面氧缺陷濃度的下降，並用變溫電性量測銅銦鎵硒太陽能電池元件表現，證實介面再復合作用的鈍化以及改善的電性翻轉情況。經由電化學表面鈍化作用處理後的銅銦鎵硒太陽能電池元件表現可從原先的4.7%能源轉換效率提升至7.7%。 (iv) 我們提出單步驟混合式電化學沉積法沉積銅鋅錫硫薄膜，此方法結合了電泳沉積和電鍍沉積兩種技術。初沉積的銅鋅錫硫薄膜成分原子百分比依序為25.33 at%、19.44 at%、14.56 at%、40.67 at%。經過一小時550度C的硫化處理後，X光繞射儀和拉曼光譜儀檢測出銅鋅錫硫薄膜有著鋅黃錫礦晶體結構的(112)、(220)、(312)X光繞射面和287 cm-1、338 cm-1拉曼A振動峰及374 cm-1拉曼B振動峰。光學吸收光譜量測出的銅鋅錫硫薄膜能階為1.48電子伏特，銅鋅錫硫太陽能電池元件表現則為350毫伏特的開路電壓、3.90毫安培每平方釐米的短路電流、0.43的填充因子及0.59 %的能源轉換效率。
並列摘要
Electrochemistry studies the electrons transfer of the chemical moieties in the electrolytic solution, thus, inert materials which only supply or withdraw electrons such as pyrolytic graphite and platinum are commonly used as the electrodes in the electroanalyses. However, in most of the cases, the materials we utilized for the working electrode are not as nonreactive as pyrolytic graphite or platinum, and will take place the chemical reactions during supplying or withdrawing electrons. We focused on investigating the chemical reaction between the chemical moieties in electrolytic solution and the working electrode materials including V-VI semiconductor of Bi2Te3, I-III-VI2 semiconductor of Cu(In,Ga)Se2, and I2-II-IV-VI4 semiconductor of Cu2ZnSnS4 and hence developed four kinds of techniques, as mentioned as follows: (i) We demonstrate an one-step electrolysis process to directly form Bi2Te3 nanosheet arrays (NSAs) on the surface of Bi2Te3 bulk with controllable spacing distance and depth by tuning the applied bias and duration. The single sheet of NSAs reveals that the average thickness and electrical resistivity of single crystalline Bi2Te3 in composition are 399.8 nm and 137.34 μΩ⋅m, respectively. The formation mechanism and the selection rules of NSAs have been proposed. A 1.12 % energy conversion efficiency of quantum-dot-sensitized solar cells with Bi2Te3 NSAs as counter electrode has been demonstrated. (ii) We propose a gas-solid transformation mechanism to synthesize surfactant-free tellurium nanowires with average diameter under 20 nm at room temperature by one-step electrochemical method. The tellurium nanowires grow along the [001] direction due to the unique spiral chains in crystal structure and show an enhanced Raman scattering effect, a broad absorption band over the range of 350-750 nm and an emission band over the range of 400-700 nm in photoluminescence spectrum. Besides, the tellurium nanowires are directly applied as p-type dopant to dope graphene and result in a right shift of Dirac point in graphene field-effect transistor. Finally, we apply these tellurium nanowires as a supercapacitor electrode and demonstrate their promising capacitive properties. (iii) We introduce a surface modification on CIGSe thin film by electrochemical treatment. After this electrochemical passivation treatment, a lower oxygen concentration near the CIGSe surface was detected by XPS analysis. Temperature-dependent J-V characteristics of CIGSe solar cells reveal that the interface recombination can be suppressed and an improved rollover condition can be achieved. As a result, the defects near the CIGSe surface can be passivated by electrolysis and the performance of CIGSe solar cells can be enhanced from 4.7 % to 7.7 %. (iv) We demonstrate a one-step hybrid electrodeposition method which combines electrophoretic and electroplated electrodeposition to synthesize CZTS thin film. To our best condition, the composition of the as-deposited CZTS thin film can be achieved to be ~25.33 at%, ~19.44 at%, ~14.56 at%, and ~40.67 at% for Cu, Zn, Sn, and S elements, respectively. After the 550°C sulfurization for 1 hour in a sulfur vapor atmosphere, three diffraction peaks corresponding to the (112), (220), and (312) planes of CZTS could be detected in XRD spectra. The A Raman-active vibration modes at 287, 338 cm-1 and B Raman-active vibration modes at 374 cm-1 could be identified as kesterite CZTS in Raman spectra. An appropriate optical property of 1.48 eV band gap is achieved for photovoltaic application. Through careful analysis and optimization, we are able to demonstrate CZTS solar cells with the VOC, JSC, FF and η of 350 mV, 3.90 mA/cm2, 0.43 and 0.59 %, respectively.