鈣鈦礦太陽能電池之光吸收層材料製備與特性分析

Abstract

本研究第一部分以反溶劑法結合快速長晶製程，經退火處理製備高結晶性之CH3NH3PbI3薄膜。藉由改變CH3NH3PbI3薄膜厚度及退火溫度，探討二者對於CH3NH3PbI3薄膜及太陽能電池元件之影響。在薄膜厚度升高時，由於光吸收效率增加，使得轉換效率提升至14.86%。當薄膜厚度大於載子擴散距離時，會造成載子於光吸收層內發生再結合現象，導致轉換效率下降。在最佳化之CH3NH3PbI3薄膜之厚度下，進行退火溫度對CH3NH3PbI3薄膜及元件特性的分析。在80℃的退火溫度下，CH3NH3PbI3薄膜之表面形貌與一般常見之100℃的條件相似，使其亦可表現出與100℃之退火條件相當的轉換效率。此結果顯示利用反溶劑法並結合快速長晶製程，CH3NH3PbI3薄膜可於較低之退火溫度製備，增加其應用於軟性基板之潛力。 第二部分透過改變甲基碘化胺(CH3NH3I)及二氧化鉛(PbI2)於前驅液中之比率，研究其比率(m)對CH3NH3PbI3薄膜之材料特性與元件之光電特性的影響。當m值由0.8增加至1.0時，可促進反應生成CH3NH3PbI3，使其結晶性提升，薄膜晶粒之大小及光吸收率亦有上升的趨勢。晶粒大小的提升減小了載子於晶界發生再結合的機率，而吸收率的提升使得光生載子數增加，使得元件之電性表現會隨著m值的增加而上升。故在m = 1時，具有最佳的元件光電轉換效率。當m 值增加至1.2時，薄膜粗糙的表面形貌與不均勻覆蓋使得於吸收層與電洞傳輸層間之載子再結合機率提高，造成元件電性表現劣化。由本研究結果顯示，透過調控反應前驅液之組成比例，可有效改善CH3NH3PbI3薄膜及電池元件之光電特性。

In the first part of this study, the fast crystallization process with anti-solvent method and post-annealing treatment were conducted to prepare CH3NH3PbI3 thin film. The thickness of CH3NH3PbI3 thin film and temperatures of post-annealing treatment were changed to investigate the effects on the morphology and photovoltaic properties of the obtained thin films and solar cells. When the thickness of thin film was increased, the conversion efficiency was up to 14.86% due to the increase of light harvesting efficiency. As the CH3NH3PbI3 film thickness was further increased, the film thickness exceeded the carrier diffusion length, resulting in carrier recombination. Hence, the conversion efficiency of the fabricated solar cells were decreased. When the annealing temperature was conducted at 80℃, the photovoltaic properties of solar devices fabricated with CH3NH3PbI3 thin film was similar to which conducted at 100℃ owing to the slight change in morphology of CH3NH3PbI3 thin film. Using fast crystallization process with anti-solvent method, low-temperature annealing produced high efficiency solar devices, increasing the potential to application of flexible substrates. In the second part of this study, the properties of CH3NH3PbI3 thin films prepared with various molar ratios of CH3NH3I and PbI2 were investigated. The molar ratios of CH3NH3I to PbI2 were denoted as m. As the value of m was increased from 0.8 to 1.0, the conversion of PbI2 to CH3NH3PbI3 was promoted. The increasing CH3NH3PbI3 compound enhanced the crystallinity, grain size and absorptance of CH3NH3PbI3 thin films. Large grain size reduced the carrier recombination at grain boundary. The improved absorptance increased the photo-generated carriers. Hence, the conversion efficiency was increased with the value of m increasing. As value of m equaled to 1, the fabricated CH3NH3PbI3 solar device showed optimized efficiency. However, once the value of m increased from 1.0 to 1.2, the rough surface and poor coverage of CH3NH3PbI3 thin films increased the carrier recombination between absorber layers and hole-transport layers, resulting in dramatic decrease in conversion efficiency. This investigation showed that the photovoltaic properties of CH3NH3PbI3 devices were improved effectively with well-controlled composition of CH3NH3PbI3 precursor.