| 摘要註: |
考量高效率太陽能電池，高聚光大電流操作下，若能有效降低元件之串聯電阻，減少電池本體之功率消耗，將有利於減緩元件之「填充因子」(Fill Factor,FF)隨著光強度提高而劣化的程度，進而提高聚光操作下之轉換效率。本論文旨在研究電極樣式及其相應電阻大小與功耗的關係，經多方考量金屬遮蔽率、電極間距、電流匹配、電流收集面積與微影製程限制...等重要因素後，提出三種新樣式優化電極之設計，包括兩種單漸變樣式：一為與電流收集面有關之階梯式線寬電極樣式(Step Width, SW)、二則與電流方向有關之線寬漸變樣式(Taper)，以及一種結合上述兩種設計概念之雙漸變樣式(SW & Taper)。本論文透過演繹優化電極之理論功耗，配合數值模擬評估其電流密度分布，完成可行性評估後，根據計算結果與設計流程完成光罩設計，並將之導入具店及保護及電池元件單元隔離之優化製成，完成接面太陽電池元件之製作。研究結果顯示，當樣品大小為1mm2時，相較於1Sun(AM1.5)之結果，於116xSuns聚光下，優化電極可明顯減緩元件「填充因子」的劣化程度，電極設計與「填充因子」劣化程度之趨勢為：Normal>SW>Taper>SE & Taper。對照組織填充因子(極限寬無漸變之設計：Normal)劣化達8.8%(FF=86.4%→FF=78.8%)，最佳設計(SW & Taper)之填充因子僅劣化2.1%(FF=87.1%→FF=84.8%)；且於116xSuns條件下有效提升轉換效率(η)最佳達18.2%(Taper)(η=23.6%→η=27.9%)，但對照駔僅提升轉化效率11.8%(η=22.9%→η=25.6%)。為近一步將本研究之設計導入更高光倍率(500x~1000x Suns)之量測及驗證，考量樣品大小為1mm2之太陽能電池因受光面積過小，其電流大小無法滿足高聚光量測機台之規範，因此將樣品尺寸提升至3mm2,4mm2和5.5mm2三種。初步研究結果顯示，於60x Suns(AM1.5)條件下，本論文所提之新樣式電極，尺寸3mm2樣品其填充因子與轉換效率均優於對照組[Step width (FF=82%, η=9.85%), Taper(FF=82%, η=9.64%), SW & Taper(FF=80.4%, η=9.67%)]>[Normal(FF=79.8%, η=9.17%)]；另外，尺寸5.5mm2之樣品其填充因子[Step width(FF=78.2%, η=12.02%)]>[Normal(FF=75.1%, η=11.03%)]，此批樣品所量得太陽能電池效率甚低，可能原因為元件表層之歐姆接觸層(GaAs)蝕刻不完全，造成表面橫向電流消耗過大，為確保此一表層障礙不再發生，在後續元件製程上採用選擇性濕式蝕刻徹底移除此一歐姆接觸層，但發現溼蝕刻造成之undercut會導致最細線寬之電極脫落(2µm)，因此本研究導入「步階式溼式蝕刻製成」(Mutiple-Step Etching)，目前已經完成新一批樣品之製作，待切割完成，即能開始進行後續量測及相關驗證工作。Consifering the high-efficiency solar cells operating under high concentrarion light intensity with high current, if the series reistance of divices can be reduced to lower power loss of solar cells, it will benefit in maintaining solar cells having a higher fill factor(FF)to improve its conversation efficiency for high concentration operation.In this thesis, we aim to study the relationship between eletrode resistance and power loss for various novel developing electrode resistance and power loss for various novel developing electrode patterns. By trade off device performances from those cosiderable parameters realated to electrode designs, including metal shadow ratio, grid pitch, current matching, current collecting effective area, photolithography limit, etc, we present three different types of novel optimized electrode-including two 1D-evolution patterns:(1)"Step Width, SW"-width evolution proportional to the effective current flow firection and current accumulation, and one one 2D-evolution pattern which combines the design ideas of (1) and (2)toghther, called (3)"SW & Taper". Un this study, the electode power consumption has been evaluated by theoretical analytics; meanwhile the current density distribution has been identified by numerical analytics; meanwhile, the current density distribution has been identified by numerical simulation. According to calucated parameters, a specific photolithography mask correspnding to our electode design rules has been prepared. Finally, novel electrode patterns embedded multi-junction solar cells have been successfully fabricated by introducing them into an optimized developed fabrication process, incleding grid protection and until cell isolation by SiO2. According to the experimental result, the developed novel elecrodes can significantly depress the fill-factor's getting worse speed.To compare devices performances under 116x Suns and 1 Sun (AM1.5)cinditions, the deterioration of fill factor from the reference design (w/o width evolution, named"Normal") can reach to 8.8% (FF=86.4%→78.8%); however, the best one from "SW & Taper" can keep a higher fill factor and only 2.1% decreased (FF=87.1%→FF=84.8%). It hence contributes to uncrease conversation efficiency (η). In case of "Taper" , 18.2% efficiency improvement can be reach(η=23.6%→η=27.9%); however, in case of "Normal", it only increase 11.8%(η=22.9%→η=25.6%). On the other hand, we have demonstrated the deterioration tren of the fill factor is Normal>SW>Taper>SW & Taper. This featire not only matches to our expection, but also consistent with theoretical analysis and numerical simulation results. |