非鉛系鈣鈦礦太陽能電池於光電之應用

Abstract

鈣鈦礦（APbX3）材料的發現，提供了製造低成本太陽能電池的解決方案，其效率可與高成本的矽太陽能電池競爭。它們易於加工和可調性也使它們在發光器件中具有吸引力。即使其太陽能電池的效率非常高，鈣鈦礦也存在高毒性鉛（Pb）和低穩定性方面的主要問題。銻（Sb）是一種有前途的元素，最近已被廣泛地研究以替代鉛。 為了解決穩定性問題，研究人員對完整的無機鈣鈦礦進行了研究。儘管基於銻的鈣鈦礦（Cs3Sb2I9）可能顯示出潛在的光伏行為，但其需高溫處理製程和SbI3的易蒸發性，使得Cs3Sb2I9的化學計量變得難以控制。本研究通過新穎的前體-蒸氣輔助溶液加工法成功地，合成Cs3Sb2I9高溫層多晶型物，且發現在倒置太陽能結構元件中，本方法所製成太陽能電池在全無機無鉛鈣鈦礦太陽能電池中的性能最高。 原則上，好的吸光材料應該是好的發光材料，但是用於發光器件和太陽能電池的材料需要不同的設計原理。本研究通過分別用SbBr3或SbCl3處理CsI：SbI3旋塗膜，並採用氣相-陰離子交換法（V-AEM）將結構組成從Cs3Sb2I9更改為Cs3Sb2Br9或Cs3Sb2Cl9。這種新穎的方法無需溶液即可使用溶解性差的前體（例如，CsCl，CsBr），通過溶液處理促進了Cs3Sb2Br9或Cs3Sb2Cl9的元件製備。本研究亦展示了使用Cs3Sb2I9的可見電致發光元件，Cs3Sb2I9層夾在空穴(ITO / PEDOT：PSS)和電子注入電極(TPBi / LiF / Al)之間。 由於SbI3的汽化溫度低，Cs3Sb2I9的層相的高溫結晶使其難以控制其形態。而且，層狀結構的缺點是沿平行八面體層於平面角的共享選擇方向。低溫下形成的二聚體相性能較差，需要改善以形成更好的形態和均勻的膜。鈣鈦礦型銻的無機二聚體相的結晶可通過使用逐步溫度退火以及使用S-供體（硫脲）和O-供體（NMP）的路易斯鹼來形成加合物而減緩反映。首次研究了Cs+，Sb3+陽離子與“ -S”和“ -O”供體路易斯鹼的加成反應。通過路易斯酸鹼加合物方法使用緩慢結晶，效率提高了約100％。除了效率外，還發現NMP可以增加薄膜以及太陽能電池的穩定性（濕度，光和熱），而TU則降低了穩定性。 探索了Cs3Sb2I9的兩種多晶型物後，顯然下一步是尋找其在獲得高效太陽能電池中的用途。鉛基無機鈣鈦礦應是高效熱穩定鈣鈦礦太陽能電池的選擇。不幸的是，在室溫下，α-CsPbI3傾向於降解為不希望的δ相（帶隙為2.8 eV）。使用較小的陽離子Sb3 +（0.76Å）來部分替代Pb2 +（1.19Å）以生產微應變，以在室溫下實現穩定的光敏γ相，初步工作得出太陽能電池的效率為7.5％，據我們所知這是γ- CsPbI3在倒置元件架構中的最佳效率。 本論文亦報導了通過用互補吸收性的有機材料，以製成異質結來進一步提高效率的初步結果。

The discovery of lead halide perovskites (APbX3) opened the gates for low-cost solution-processable solar cells with efficiencies competitive with those of high-cost Si solar cells. Their easy processing and tunability makes them attractive in light emitting devices as well. Even though the efficiencies of their solar cells can be very high, lead halide perovskites have major problems in terms of high toxicity (Pb) and low stability. Antimony (Sb) is a promising element that has recently been explored extensively as an alternative to Pb. To counter the stability issue, a complete inorganic perovskite was investigated. Although Sb-based perovskite (Cs3Sb2I9) can display potentially useful photovoltaic behaviour, but its high temperature processing and easy evaporation of SbI3 makes it difficult to control the stoichiometry of Cs3Sb2I9. A successful demonstration of high temperature layer polymorph of Cs3Sb2I9 was synthesized by the novel Precursor-Vapor-Assisted Solution-Processing. Performance of solar cell was found to be highest among all-inorganic Pb-free perovskites in inverted solar device-architecture. In principle, a good light-harvesting material should be a good light-emitting material, but the materials used for light-emitting devices and photovoltaic devices require different design principles. Vapor-Anion exchange method (V-AEM) was employed to change the structural composition from Cs3Sb2I9 to Cs3Sb2Br9 or Cs3Sb2Cl9 by treating CsI:SbI3 spin-coated films with SbBr3 or SbCl3, respectively. This novel method facilitates the fabrication of Cs3Sb2Br9 or Cs3Sb2Cl9 through solution processing with no need to use poorly soluble precursors (e.g., CsCl, CsBr). A visible electroluminescence from device employing Cs3Sb2I9 emitter sandwiched between ITO/PEDOT:PSS and TPBi/LiF/Al as hole and electron injection electrodes, respectively was demonstrated. The high temperature crystallization of layer phase of Cs3Sb2I9, makes it difficult to control its morphology because of the low vaporization temperature of SbI3. Also, layered form has a disadvantage of choosing orientation along the planes which are parallel to the layers of corner sharing octahedra. The low temperature dimer phase lacks in performance and need to be explored more with better morphology and uniform films. Crystallization of all inorganic dimer phase of Sb perovskite has been retarded by using gradual temperature annealing accompanied by use of S-donor (thiourea) and O- donor (NMP) Lewis bases for adduct formation. Cs+, Sb3+ cations have been studied for the first time to make an adduct with “–S” and “–O” donor Lewis bases. The efficiency was increased ~100 % by using slow crystallization via Lewis acid-base adduct approach. In addition to efficiency, NMP was found to increase the stability (humidity, light as well as heat) of the film as well as solar cell while TU reduced the stability. Having explored both polymorphs of Cs3Sb2I9, the next obvious step is to look for its use in obtaining high efficiency solar cells. The Pb based inorganic perovskite can be a good option for high efficient thermally stable perovskite solar cells. Unfortunately, at room temperature, α-CsPbI3 has the tendency to degrade to the undesired δ-phase (bandgap 2.8 eV). Smaller cation Sb3+ (0.76Å) is used to partially substitute Pb2+ (1.19 Å) to produce micro-strains for realizing stabilized photoactive γ-phase at room temperature and the initial work gave an efficiency of 7.5 % which is the best efficiency for γ-CsPbI3 in inverted device architecture to the best of our knowledge. Preliminary results of further improvement in efficiency by making heterojunction with complimentary absorbing acceptor organic materials is also reported. The heterojunction showed impressive increment in efficiency while maintaining good transparency and thus making them a good material to be explored for transparent photovoltaics.