具新型載子傳導材料之鈣鈦礦太陽能電池的光伏與缺陷性質研究

Photovoltaic Performance and Defect Analysis of Perovskite Solar Cells with Novel Carrier Transport Layers

謝孝基(Hsiao-Chi Hsieh)

指導教授 ： 林金福

共同指導教授 ： 王立義

國立臺灣大學/工學院/材料科學與工程學研究所/博士(2019年)

https://doi.org/10.6342/NTU201900711

摘要

本論文分別利用溶膠凝膠法和超音波輔助噴霧裂解法製作電子傳導層，再利用旋轉塗佈法製作吸光層，依序沉積在導電玻璃上。隨後塗佈上改良的電洞傳導層，以製備一N-I-P層狀結構之鈣鈦礦太陽能電池元件。本研究首先利用醌型結構(DIQ-C12)取代傳統小分子電洞傳導層材料(spiro-OMeTAD)，改善spiro-OMeTAD在紅光波段吸收較弱及低成膜性等缺點。再利用二維結構之聚噻吩(PBTTTV-h)取代高分子電洞傳導層材料，試著減少電洞傳導材料層與鈣鈦礦吸光層之能障差，探討PBTTTV-h對太陽能電池元件之光電轉換效率的影響。在本研究中，分別利用掃描式電子顯微鏡、X光繞射儀、紫外-可見分光光度法、表面功函數量測儀觀察材料結構及其特性。時間解析光激螢光、電化學阻抗頻譜、電荷式深能階暫態能譜等分析方法觀察太陽能電池元件之光電特性與缺陷密度分佈狀況。
本研究主要可分成四個部份。其一，分別利用溶膠凝膠法和超音波輔助噴霧裂解法製作鈦氧化物(TiO2)電子傳導層，探討不同電子傳導層之製程方法對鈣鈦礦吸光層的影響。發現用超音波輔助噴霧裂解法形成之TiO2層，具有高緻密性及低孔隙度之特色，可助鈣鈦礦吸光層形成大顆粒的晶粒，進而減少鈣鈦礦吸光層與電子傳導層及電洞傳導層間的介面電阻值。同時亦提升其光電轉換效率到~16.13%。
其二，利用醌型結構取代傳統小分子電洞傳導層材料(spiro-OMeTAD)。結果發現DIQ-C12可增強太陽能電池元件在500~600奈米波段之光源吸收能力，且電洞傳導層之厚度可減少到150奈米，為傳統小分子電洞傳導層之一半。其光電轉換效率最高可達12.22%。
其三，利用具二維結構之聚噻吩取代傳統高分子電洞傳導層材料(P3HT)。其鈣鈦礦吸光層、PBTTTV-h和P3HT之功函數分別為5.30 eV、4.94 eV和4.80 eV。因鈣鈦礦吸光層與PBTTTV-h之功函數較為相近，可提高約0.13 eV開環電壓。又PBTTTV-h結構塗佈於鈣鈦礦層時，結構排列更趨近face-on，可助於電洞傳輸之能力。光電轉換效率可提升到14.8%。元件在高相對濕度(~90%)環境中測試一天，仍可維持其85%之光電轉換效率。
其四，利用電荷式深能階暫態能譜觀察不同電洞傳導材料層內部及其與鈣鈦礦吸光層之界面的缺陷密度分佈。其中發現PBTTTV-h電洞傳導層內部和與吸光層之界面上，均具有較低的陷域濃度。推測此可能為導致低電荷捕捉及再複合速率之因素，進而降低太陽能電池元件遲滯現象之產生和提高元件性能。

關鍵字

鈣鈦礦太陽能電池 ； 電子傳導材料 ； 電洞傳導材料

並列摘要

In this dissertation, electron transport layers were respectively deposited on the conductive glass by sol-gel (SG) and ultrasonic spray pyrolysis (USP) methods. Then, light-absorbing layers and hole transport layers were sequentially deposited by the spin-coating method. Perovskite solar cells in an N-I-P structure were fabricated based on the proper parameters. The heterocyclic quinoid-based hole transporting materials (HTMs) with a rigid quinoid core [3,6-di(2H-imidazol-2-ylidene)-cyclohexa-1,4-diene] were first utilized to replace the common small molecular HTM (2,2’,7,7’-tetrakis-(N,N-di-4-methoxyphenylamino)-9,9’-spirobifluorene, spiro-OMeTAD) to improve the absorption in the near-infrared region and film-formation properties. Later, the two dimensional conjugated polymer, PBTTTV-h, was utilized to replace the common polymeric HTM (poly(3-hexylthiophene-2,5-diyl), P3HT) to improve photovoltaic properties. Material characterizations are conducted by the scanning electron microscope, X-ray diffractometer, UV/VIS spectrophotometer, and photoelectron spectroscopy. The photovoltaic performances and defect distribution were examined by the time-resolved photoluminescence, electrochemical impedance spectroscopy, and charge-based deep level transient spectroscopy.
This dissertation consists of four parts. In the first part, the compact TiO2 layer was deposited on the conductive glass by SG and USP method, respectively. According to my investigation, the titanium dioxide layer prepared by USP method has the ultra-compact, bulk-like film, which is helpful to assist the formation of large crystallite grains of perovskite layer on compact TiO2 and reduce the interfacial resistances between the perovskite layer and compact TiO2. Therefore, the power conversion efficiency (PCE) of TiO2-USP devices was improved to 16.13%.
In the second part, the DIQ-C12 was utilized to replace the common small-molecule HTM (spiro-OMeTAD). Depending on my investigation, the DIQ-C12 was found to possess very intense absorption in the 500-600 nm region, and the thickness of the hole transport layer in DIQ-C12-based devices can be reduced to ~150 nm, which is one half of the common small-molecule hole transport layer. Besides, the PCE of DIQ-C12-based devices was improved to 12.22%.
In the third part, a conjugated polythiophene with a two-dimensional conjugated structure was utilized to replace the poly(3-hexylthiophene-2,5-diyl) (P3HT). The work functions (WFs) of the perovskite, PBTTTV-h, and P3HT were 5.30 eV, 4.94 eV, and 4.80 eV, respectively. The WF of perovskite layer is much close to that of PBTTTV-h, thus increased the VOC (near 1 V). The PBTTTV-h layer, which was prepared by spin coating on perovskite surface, was self-assembled into an ordered structure with a face-on orientation, which can improve the hole transport capability. The PCE of PBTTTV-h-based devices was improved to 14.8%.
In the fourth part, the defect distribution in the intrinsic layers of several HTMs and their perovskite/HTM interfaces was examined by the charge-based deep level transient spectroscopy. The lowered defect concentration, which was found at intrinsic PBTTTV-h layer and the perovskite/PBTTTV-h interface, may be associated with the lowered charge trapping and recombination rate, hence reduced hysteresis phenomenon and improved photovoltaic performances.

並列關鍵字

perovskite solar cells ； electron transport material ； hole transport material

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