高效率混合鹵素型寬能隙鈣鈦礦太陽能電池並應用於四接點鈣鈦礦/矽晶串疊型太陽能電池

Abstract

近年來，由於環保意識抬頭，非再生能源產業的各種環境議題被各界廣泛討論，例如火力發電產業對於溫室氣體的排放，或核能發電對於核廢料最終處置的方式，因此如何尋找一個乾淨且高效的發電方式，一直是近年科學家一直努力的方向。鈣鈦礦太陽能電池(perovskite solar cells, PSCs)，由於其擁有較高的光電轉換效率，以及能夠使用全溶液製成的特性，被認為非常具有商業化的潛力，而除了元件本身的效率及穩定性外，如何針對其應用端開發，也是鈣鈦礦材料研究上一個非常重要的議題。 鈣鈦礦/矽晶串疊型太陽能電池是近年來光伏領域中的熱門研究方向，藉由調整鈣鈦礦的能隙大小，便能夠藉由串聯的方式減少單結太陽能電池中的熱馳豫損失(thermalization loss)以及吸收損失(absorption loss)現象，是目前最有希望打破 Shockley−Queisser 極限 (S−Q limit) 的方式，藉由上下電池分工吸收不同波段的光，便能夠進一步朝向突破單結太陽能電池最高理論效率邁進(~33%)。然而，寬能隙鈣鈦礦最主要的問題是開路電壓的損失，以及光致相分離現象。這些現象主要是來自於主動層中大量存在的缺陷，這些缺陷會在主動層內部或是表面形成陷阱能階，導致載子發生非放射性複合，以及引發離子遷移所導致的光致相分離，造成寬能隙鈣鈦礦元件效率表現不佳。 本研究使用銫-甲咪混合離子系統，藉由調控銫離子與溴離子含量改變鈣鈦礦的能隙，並發展出能隙1.65eV的高光穩定性寬能隙鈣鈦礦組成Cs0.30FA0.70Pb(I0.85Br0.15)3，於532nm波長之雷射激發10分鐘後，光致發光訊號僅位移6.38 nm。為了進一步提升銫-甲咪混合離子系統相對較差的載子擴散長度，使用銣離子摻雜提升寬能隙鈣鈦礦的元件表現，無論是從與載子傳輸層間的能階匹配度、缺陷密度，以及離子遷移的表現上，銣離子摻雜的寬能隙鈣鈦礦表現都有相應的提升。銣離子摻雜的元件表現相較於無摻雜的鈣鈦礦，平均光電轉換效率由原先的18.59%提升至20.54%，最高效率可以達到21.95%，為目前能隙1.6eV以上的反式寬能隙鈣鈦礦元件中最佳。而根據此鈣鈦礦系統所製備之四接點鈣鈦礦/矽晶串疊型太陽能電池效率則可以達到28.97%，亦為目前反式寬能隙鈣鈦礦元件中最高的效率表現。

In recent Years, because of the rise of environmental awareness, various environmental issues about the non-renewable energy industry have been widely discussed, such as the greenhouse gas emissions from the thermal power plant or the final disposal of nuclear waste from nuclear power generation. Perovskite solar cells (PSCs) are considered to have potential for commercialization due to their high photovoltaic efficiency and solution processable. By adjusting the bandgap of the perovskite, it is possible to reduce the thermalization loss and absorption loss in single-junction solar cells by connecting them in series, which is the most promising way to break through the Shockley-Queisser limit. By dividing the absorption of light between the upper and lower cells, it is possible to move further towards breaking the theoretical maximum efficiency of single-junction solar cells (~33%). However, the main problem with wide bandgap perovskite is the photoinduced phase segregation and the loss of open-circuit voltage. These phenomena are mainly due to the presence of a large number of defects in the active layer, which can form trap energy levels within or on the surface of the active layer, leading to non-radioactive recombination of carriers and photoinduced phase segregation due to ion migration, resulting in poor efficiency. In this study, we use cesium-formamidinium mixed cation system to optimize the energy gap of perovskite by changing the content of cesium and bromine ions, and successfully develop a highly photos stable wide bandgap perovskite composition: Cs0.30FA0.70Pb(I0.85Br0.15)3 with a bandgap of 1.65 eV. After 10 minutes of laser excitation at 532 nm, the photoluminescence signal was only displaced by 6.38 nm.

To further enhance the relatively poor carrier spreading length of the Cs-FA mixed cation system, Rb ion was used to enhance the performance of the wide bandgap perovskite, in terms of energy level matching with the carrier transport layer, defect density, and ion migration performance. Rb-doped devices show an increase in average photovoltaic conversion efficiency from 18.59% to 20.54%, with a maximum efficiency of 21.95%, which is the best inverted perovskite solar cell devices with a bandgap larger than 1.6eV. The efficiency of the four-terminal perovskite/ silicon tandem solar cell based on this this system can reach 28.97%, which is also the highest performance compare to other researches base on inverted structure so far.