鈣鈦礦太陽能電池是目前效率最高的固態太陽能電池。其中的鈣鈦礦材料是高效率固態太陽能電池的關鍵材料，而混合鈣鈦礦結構中心的有機分子是影響其太陽能電池穩定性以及電子特性的重大主因。
本研究利用第一原理計算有機無機混合鈣鈦礦APbX3（A = CH3NH3+簡寫MA， NH2CHNH2+簡寫FA，X = Cl, Br, I），總共有六種不同鈣鈦礦並針對其優化的幾何結構和電子特性做探討。分析它們的有機分子如何有影響鈣鈦礦的主要結構，分析屬於鈣鈦礦框架Pb及不同的鹵素原子X於能帶結構、軌域、態密度以及電荷密度的影響，藉由這些分析結果討論鈣鈦礦材料的電子特性和光學性質以及穩定性。此外，我們比較有機分子FA和MA系統的不同，對於能隙、穩定度、電子雲分佈的均勻度還有遲滯特性的探討。
研究結果發現，無論是MA還是FA有機分子鈣鈦礦系統的幾何優化的結構都有使Pb和鹵素原子X框架向外撐出產生扭曲，使得對稱性下降。而在能隙主導的部分，由電子結構圖和態密度圖能看出，導帶部分為Pb的p軌域做主導，價帶為鹵素X的p軌域作主導，碘原子較特殊，價帶為碘的6p及6s軌域作主導。可以看出APbX3中，APbI3因為能態多而電子傳輸路徑多和效率較高有很大的關係。
鈣鈦礦中心有機分子的部分，FAPbX3系統的鈣鈦礦在電荷分佈均勻度上由態密度投影實空間圖可看到FA態密度比起MA的態密度是由較均勻的電子雲撐起鈣鈦礦框架，使立方體結構穩定性高；由數值電偶極矩表示得出，FA的電偶極矩小於MA的2~3倍左右，電子雲分佈較均勻且不易有電荷遲滯的現象產生，是良好的太陽能吸光及電子電洞傳輸材料。

The perovskite solar cell is the highest efficiency solid-state solar cell, popping up in recent years. Organic-inorganic hybrid perovskite is the key materials for high efficiency solid-state solar cells.
In this work, we study the geometric and electronic properties of organic-inorganic hybrid perovskite, APbX3 (A = CH3NH3+ ,=MA and NH2CHNH2+,=FA, and X = Cl, Br, I) from first principles. Particularly, their geometries, band structures, orbitals, density of states, and the charge densities are analyzed, revealing the electronic and optical properties, as well as the stability, of such materials. In addition, we compare the band gap of FAPbI3 with the measured data. Finally, we compare the electronic features of FAPbX3 with MAPbX3.
The results show that not only MA but also FA cations after structural optimization will disturb the frame of perovskite and make the structure asymmetry. In E-K diagram, the p orbital of the Pb atom affects the conduction band minimum, while the p orbitals of the Cl (Br) atoms influence the valence band maximum. The band structure for APbI3, the p orbital of the Pb atom controls the conduction band minimum, while the s and p orbitals of the I atoms dominate the valence band maximum. The valence band maximum of APbI3 is closer to the Fermi energy and has larger density of states, so this material can generate and
transfer more electrons than other hybrid perovskites.
Compare with FA cations and MA cations, We calculate the dipole of the perovskite. The density of state of FAPbX3 are more uniform distribution than the MAPbX3 in the real space. the charge distribution of FA cations are larger than MA ones, supporting that FA cations interact with the Pb-X frame stronger than MA, making the systems more stable. We show the value of the electric dipole moment that dipole of FAPbX3 are reduce than two to three times of MAPbX3.The electron cloud of FA cation is more uniform distribution and less hysteresis phenomenon. As a result, FAPbX3 will be a good light-absorbing material and also good for carrier transmission in perovskite solar cells.

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