| Summary: | 博士 === 國立臺灣大學 === 材料科學與工程學研究所 === 107 === 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.
|
|---|
