鈣鈦礦太陽能電池之異質成核機制與其光電性質研究

本研究將表面覆有I^-配體的硫化鉛奈米晶體(PbS/I^-)混入CH3NH3PbI3-xClx前驅物溶液中來改變鈣鈦礦的結晶行為。在結晶過程中，硫化鉛量子晶體表面的I^-配體將與CH3NH3PbI3-xClx的前驅物反應使CH3NH3PbI3-xClx在奈米晶體表面異質成核，原本於空間中均勻分散的晶核核點因此集中於PbS奈米晶體表面異質成核，這使得鈣鈦礦於成長時具有較大的成長空間。我們發現於此條件下成長完成之後的CH3NH3PbI3-xClx晶粒大小達4μm。我們後續將此鈣鈦礦製作成FTO/TiO2/CH3NH3PbI3-xClx/Spiro OMeTad/Au 之平面結構太陽能電池，我們發現，此太陽能電池之填充因子高達77.60%，且光電轉換效率為16%，我們推測這是因為鈣鈦礦晶粒的變大而使得其載子傳輸性質提升。為了瞭解晶粒大小與載子傳輸性質關係，本研究利用時間解析光致螢光與雙極性載子傳輸方程搭配特殊的CH3NH3PbI3-xClx元件結構來分析CH3NH3PbI3-xClx的載子擴散長度。由測量的結果發現，晶粒較大的鈣鈦礦薄膜具有較長的電子與電洞擴散長度(1405nm與1329nm)。我們推測係因大晶粒的鈣鈦礦單位長度內的晶粒邊界較少，使得載子在其中得以更加順利的擴散至電極，如此可以說明混入PbS/I^-之鈣鈦礦太陽電池如何具有優異的表現。根據此研究的結果，我們可以藉由PbS/I^-奈米晶體與CH3NH3PbI3-xClx的混合，而得到晶粒較大的CH3NH3PbI3-xClx薄膜，且其具有優異的載子傳輸性質，因此我們得以製作出表現較佳的CH3NH3PbI3-xClx太陽能電池。

關鍵字

PbS ；鈣鈦礦；奈米晶體； CH3NH3PbI3-xClx ；太陽能電池

並列摘要

In this work, we proposed a new idea using inorganic nanocrystals of PbS/I^- as additive and nucleus to improve thin film morphology in planar perovskite (CH3NH3PbI3Cl3-x) solar cells by promoting heterogeneous nucleation of perovskite crystals. By mixing PbS/I^- nanocrystals into perovskite precursor, our proposed method showed a large improvement in gran size (exceeded 4 um) and superior photon to electron converting efficiency of FTO/TiO2/CH3NH3PbI3-xClx/Spiro OMeTad/Au planar structure solar cell ( PCE=16% FF=77.60% ). We proposed the increase of Jsc and FF could be attributed to greater carrier transport properties. We performed diffusion length measurements of large grain perovskite by TRPL quench dynamic and ambipolar transport equation. Both electron and hole diffusion length of large grain perovskite are longer than the normal one (1405nm and 1329nm). This result indicates that the smaller trap densities in these larger grain size crystals, and therefore reduced charge transfer resistance across the perovskite crystal that grew from PbS/I^-, so that achieved the higher FF and Jsc. Once the grain size of perovskite was increased by PbS/I^-. The charge traps which photo-generated carrier encountered under diffusion process are less than the pristine sample, therefore we can perform high efficiency perovskite solar cell.