전하전달층의 전하추출에 대한 연구와 페로브스카이트 태양전지에의 응용

Abstract

Recently, perovskite solar cells (PSCs) are attracting much attention because of the wide absorption wavelength range of the perovskite light absorbing material and the high efficiency of converting photons to free charge carriers. Most studies focus on the perovskite layer itself to improve the device efficiency. Although the device efficiency was improved due to intensive studies, additional studies for investigating the relationship between charge transport layer and power conversion efficiency (PCE) are needed. In order to propose a new direction in this situation, I investigated the charge carrier behavior in the interface between the perovskite optical absorption layer and the electron or hole transport layer, and clarified the conditions for obtaining an efficient solar cell device. Here, I briefly discuss the developments in the perovskite solar cell and attempt to give a systematic introduction about the charge transport layer for highly efficient PSCs in introduction part. Part 1 and part 2 are the results of my works to determine what properties are required in the electron or hole transport layer to achieve high PCE. In part 1, I optimized the bilayer structure of the electron transport layer (ETL) with spin-coated tin oxide (SnO2 ) and anodized titanium oxide (a-TiO2 ). The effect of the interface charge extraction and the electron transfer rate in the electron transport layer on the optical properties was studied. We developed spin-coated SnO2 on anodized TiO2 (SnO2@a-TiO2 ) bilayer as the ETL of planar PSCs. We found that SnO2@a-TiO2 bilayer, where SnO2 layer is deposited onto TiO2 film, is favourable structure to improve device performance because of excellent intrinsic properties of low temperature annealed SnO2 layer, including high electron mobility and efficient electron extraction. The geometrical properties of SnO2@a-TiO2 bilayer were improved by replacing spin-coated TiO2 layer with a-TiO2, and the SnO2@a-TiO2 bilayer exhibited well-defined geometry with increased vertical uniformity, decreased grain boundaries, and defect-free contact with rough foluorine-doped tin oxide (FTO). Due to these advantages, SnO2@a-TiO2 bilayer exhibited a high power conversion efficiency of 18.6% in planar perovskite solar cell, and the photoluminescence (PL) quenching and decay results clearly revealed the increased electron extraction ability of SnO2@a-TiO2 bilayer compared to bare TiO2 ETL. In part 2, I investigated hole transport layer (HTL) and interface between HTL and perovskite. I have studied the conditions of conducting polymers that can be used as a hole transport material (HTM), and I have applied a donor-acceptor copolymer based on benzothiazole and benzodithiophene to perovskite solar cells. Poly (2,10-benzothiophene-thiophenebenzodithiophene) (P(2,10-BT-T-BDT)) exhibits high hole mobility of about 10-3 m/V s. It was shown that the thickness of 50 nm was suitable regardless of the solvent. We also compared the properties of poly (6,6-benzothiophene-thiophene-benzodithiophene) (P (6,6-BT-T-BDT)) substituted with an alkyl group to confirm the importance of pi-pi stacking between molecules. In addition, this study is meaningful in that HTM is employed using an environmentally friendly solvent, not toxic solvent which has halogen atoms.