鈣鈦礦材料物性探討及鈣鈦礦太陽能電池製備

Abstract

本篇論文第一部分對MAPbI3鈣鈦礦材料進行10 K ~ 300 K變溫的光致螢光光譜研究，並探討其螢光能量、強度與半高寬隨著溫度而改變之原因。第二部分為MAPbI3鈣鈦礦太陽能電池元件的製備、填充程度與鈍化作用對效率表現的探討。

在變溫光致螢光中，在約150 K即可由XRD觀測到四方相的轉變，而正交相的螢光訊號則在約110 K ~ 120 K產生。 由SEM觀察，在MAPbI3晶界處仍存在約10 nm小晶粒，推論因其誘發量子侷限效應，導致MAPbI3能隙間存在不同侷域態，使變溫PL量測到異於一般半導體的升溫藍移現象，正與自組裝量子點的行為模式類似。 隨著溫度上升，在能量方面，四方相從1.596 eV些微藍移至1.598 eV，再紅移至1.57 eV，再藍移至1.61 eV，其轉折點分別為40 K與130 K；正交相則只呈現極小幅度藍移，10 K升溫至120 K，從1.66 eV移至1.67 eV。而在半高寬方面，隨溫度上升，四方相由寬變窄從105 meV轉為49 meV，再變寬轉為94 meV，其轉折點為120 K；而正交相相對於四方相則幾乎維持一定，但仍有越來越寬之趨勢，從10 K至100 K，由38 meV轉為43 meV。

另外，在元件的部分，使用兩步驟沉積法製備多孔洞型MAPbI3鈣鈦礦太陽能電池元件，效率為6.5 %，以增加填充量的方式將效率提升至8.0 %，此外，使用矽烷醇鈍化鈣鈦礦介面以利於載子的傳輸，效率則提升至9.7 %。

This thesis is divided into two parts; the first part reports results from studies on perovskite (MAPbI3) by using temperature dependent photoluminescence spectroscopy and x-ray diffraction techniques. The photoexcited emission peak positions, intensity, and full width at half maximum (FWHM) were recorded when the temperature was scanned from 300 K to 10 K. The second part demonstrates the fabrication of perovskite solar cells and the enhancement of cell performance by the combination of improving the perovskite filling in TiO2 layer and surface passivation.

From the XRD spectra, a phase transition from the tetragonal phase (at room temperature) to the orthorhombic phase begin to take place when the temperature of perovskite was cooled down to ~ 150 K. Clear PL signals originated from the orthorhombic phase were observed around 110 K ~ 120 K. With increased temperature, the luminescence peak of the tetragonal phase first showed slightly blue-shifted from 1.596 eV to 1.598 eV at 40 K and then was red-shifted to 1.57 eV at 130 K. Above 130 K, the energy peak was again blue-shifted to 1.61 eV with temperature increased toward 300K. The luminescence peak of the orthorhombic phase showed only slightly blue-shifted from 1.66 eV to 1.67 eV with temperature increased from 10 K to 120 K. Narrowing of the FWHM of the luminescence peak of the tetragonal phase from 105 meV to 49 meV was observed with increased temperature from 10 K to 120 K. Above 120 K, the FWHM began to broaden and reached 94 meV at 300 K. The FWHM of the luminescence peak of the orthorhombic phase decreased from 43 meV to 38 meV with decreased temperature from 100 K to 10 K. In the scanning electron microscope images, nano scale grains with an average size of ~ 10 nm were observed in the MAPbI3 thin film. We speculate that, due to the presence of the nano grains, localized states were induced within the energy gap of MAPbI3 due to the quantum confinement effect. The observed temperature dependent behavior in photoluminescence spectra, which is similar to those observed in the self-assembly semiconductor quantum dots, was attributed to the presence of localized states induced by the MAPbI3 nano scale grains.

The mesoporous perovskite solar cells were demonstrated with an initial efficiency of 6.5% by using a two-step deposition method. By spinning PbI2 for two times to provide a better perovskite loading, the efficiency was improve to 8%. The efficiency was further improved to 9.7% by using the silanol to passivate the uncoordinated halide on the interface, which led to reduced surface recombination and enhanced carrier transport.