평면 이종접합 페로브스카이트 태양전지의 제작 방법과 광전 효율의 상관관계

학위논문 (박사)-- 서울대학교 대학원 : 재료공학부, 2016. 2. 조원호.Although one-step deposition method has intensively been studied because of simple and easy fabrication of perovskite films, uncontrolled crystallization of perovskite during one-step deposition often results in films with small crystallites and low surface coverage, leading to low photovoltaic performance. In this study, we have proposed the optimum processing condition to afford favorable film morphology and crystal orientation for achieving high power conversion efficiency of perovskite solar cells. First, two different morphologies, tree-like and flower-like morphologies, are developed depending upon the spin-coating time and post-heat treatment temperature. When the perovskite is crystallized from the liquid film after short spin-coating time, the flower-like morphology is developed, whereas the tree-like morphology is developed when the perovskite is crystallized for long spin-coating time. When the morphology evolution is monitored using in-situ optical microscopy and X-ray diffraction to investigate the origin of the difference between tree-like and flower-like morphologies, it reveals that CH3NH3I–PbI2–solvent complex is formed to develop the tree-like morphology before CH3NH3PbI3 crystals are formed whereas the flower-like morphology is developed when the CH3NH3PbI3 crystals are formed directly from the liquid film without formation of CH3NH3I–PbI2–solvent complex. The film with flower-like morphology, as prepared from DMSO solution, has large-sized crystallites, and the crystallites are highly orientated along (112) and (200) directions, resulting in a high PCE of 13.85%, whereas the film with tree-like morphology has small-sized crystallites with random crystal orientation, exhibiting very low PCEs. Second, we successfully fabricated CH3NH3PbI3 crystals with two different orientations to the substrate using two different organic precursors (CH3NH3I and CH3NH3Cl), and then investigated the effect of crystal orientation on the photovoltaic performance of CH3NH3PbI3 solar cells with planar heterojunction structure. The power conversion efficiency (PCE) of inverted cell (13.60%) prepared with I3 film (made from precursor CH3NH3I) is higher than that of the inverted cell (11.26%) prepared with I2Cl film (made from precursor CH3NH3Cl) mainly due to higher short circuit current (JSC) and higher fill factor (FF) of I3-based cell, whereas the PCE of normal cell (12.88%) prepared with I2Cl film is higher than that of the inverted cell (3.97%) made of I3 film. Considering that I3 and I2Cl films exhibit different crystal orientations, we realize that the crystal orientation of perovskite is directly related to PCE. The PCE difference due to different crystal orientation is interpreted by the charge carrier lifetime extracted from transient photoluminescence spectrum: Shorter lifetime affords faster charge transfer from perovskite layer to charge transport layer, thus the device with shorter lifetime exhibits higher JSC and PCE. Strong hysteresis of J–V curves of normal cells is also interpreted by slow and imbalanced charge transfer from perovskite to CTL.Chapter 1 Introduction 1 1.1 Organic-inorganic hybrid perovskite solar cells 1 1.1.1 Organic-inorganic hybrid perovskites 1 1.1.2 Physical properties of organic-inorganic hybrid perovskites 5 1.1.2.1 Optical properties 5 1.1.2.2 Bandgap and energy level 7 1.1.2.3 Exciton binding energy 9 1.1.2.4 Dielectric constant 10 1.1.2.5 Charge carrier diffusion lengths 11 1.1.2.6 Charge carrier mobilities 14 1.1.3 Device structures 16 1.2 Planar heterojunction perovskite solar cells 19 1.2.1 Operating principles 19 1.2.2 Fabrication methods for organic-inorganic hybrid perovskite film 22 1.3 Objectives of this study 29 Chapter 2 Experimental Section 33 2.1 Synthesis 33 2.1.1 Materials 33 2.1.2 Synthesis 33 2.1.2.1 Synthesis of organic precursors 33 2.1.2.2 Synthesis of titanium dioxide nanoparticles 34 2.2 Film fabrication and characterization 35 2.2.1 Materials 35 2.2.2 Fabrication method 35 2.2.3 Characterization method 36 2.3 Device fabrication and measurement 37 2.3.1 Materials 37 2.3.2 Solar cell device fabrication 38 2.3.2.1 Fabrication of devices with normal structure 38 2.3.2.2 Fabrication of devices with inverted structure 39 2.3.3 Solar cell performance measurement and device characterization 40 Chapter 3 Results and Discussion 42 3.1 Two different mechanisms of CH3NH3PbI3 film formation and its effect on photovoltaic properties 42 3.1.1 Synthesis and characterization 42 3.1.2 Photovoltaic properties 42 3.1.3 Mechanisms of CH3NH3PbI3 film formation 47 3.1.4 CH3NH3PbI3 crystal orientation 67 3.1.5 Summary 73 3.2 CH3NH3PbI3 crystal orientation and photovoltaic performance of planar heterojunction perovskite solar cells 75 3.2.1 Synthesis and characterization 75 3.2.2 CH3NH3PbI3 crystal orientation 75 3.2.3 Film morphology 81 3.2.4 Photovoltaic properties 83 3.2.5 Charge transfer characteristics 83 3.2.6 Photocurrent densityvoltage hysteresis 90 3.2.7 Summary 93 Chapter 4 Conclusions 95 Bibliography 98 Korean Abstract 112Docto

Synthesis and Characterization of Low Bandgap Polymers Containing Fluorinated Benzothiadiazole for Efficient Organic Solar Cells

OAIID:oai:osos.snu.ac.kr:snu2012-01/104/0000001236/5SEQ:5PERF_CD:SNU2012-01EVAL_ITEM_CD:104USER_ID:0000001236ADJUST_YN:NEMP_ID:A004558DEPT_CD:445CITE_RATE:0FILENAME:배승환.pdfDEPT_NM:재료공학부EMAIL:[email protected]:

Solvent evaporation-assisted crystal growth of perovskite to achieve high performance organic-inorganic hybrid solar cells

Perovskite-based organic-inorganic hybrid solar cells have recently received great attention from both academia and industry. Methylammonium lead iodide (MAPbI3) for perovskite solar cells is one of the most-commonly used compounds as a photon absorber. In this study, we have demonstrated a novel method for formation of perovskite film on the PEDOT:PSS coated substrate using DMSO as a processing solvent, where the film is formed via the solvent evaporation-assisted crystal growth. When the MAPbI3 film is fabricated by the method using DMSO as a solvent, the film exhibits a flower-like morphology with good coverage and the crystals in the film are highly oriented along the (112) direction. As a result, the pervoskite solar cell fabricated from DMSO solution exhibits a PCE of 9.29% with a JSC of 16.13 mA/cm2 while the cell fabricated from the conventional DMF solution shows a PCE of 4.52% with a JSC of 9.51 mA/cm2.OAIID:oai:osos.snu.ac.kr:snu2014-01/104/0000001236/8SEQ:8PERF_CD:SNU2014-01EVAL_ITEM_CD:104USER_ID:0000001236ADJUST_YN:NEMP_ID:A004558DEPT_CD:445CITE_RATE:0FILENAME:141008추계고분자학회_한승진.pdfDEPT_NM:재료공학부CONFIRM:

Effect of Different Charcogenophenes in Isoindigo-based Conjugated Copolymer on Photovoltaic Properties

New low bandgap conjugated copolymers composed of isoindigo as electron-deficient unit and various chalcogenophenes (thiophene, selenophene and tellurophene) as electron-rich unit were synthesized (as denoted by PIT, PISe and PITe, respectively) to investigate the effect of different chalcogenophene on the photovoltaic properties of isoindigo-based copolymers. The copolymers (PISe and PITe) show bathochromic shift in UV-Vis absorption and lower LUMO energy level as compared to its thiophene analogue (PIT). The solar cell device based on PISe blended with PC61BM exhibits a promising power conversion efficiency (PCE) of 5.72% with a JSC of 10.21 mA cm?2, which is higher than those of PIT (PCE of 3.98% and JSC of 8.34 mA cm?2), while the device based on PITe shows lower JSC and PCE than those of PIT and PISe because of its coarse morphology of the blend.OAIID:oai:osos.snu.ac.kr:snu2014-01/104/0000001236/2SEQ:2PERF_CD:SNU2014-01EVAL_ITEM_CD:104USER_ID:0000001236ADJUST_YN:NEMP_ID:A004558DEPT_CD:445CITE_RATE:0FILENAME:2014춘계고분자학회_배승환.pdfDEPT_NM:재료공학부CONFIRM:

Comparison of two D-A type polymers with each being fluorinated on D and A unit for high performance solar cells

Recently, polymers with fluorinated building block have recently attracted great interest because high power conversion efficiencies (PCEs) over 7% have been achieved by fluorination of A unit. In this work, we synthesized two kinds of D-A polymers with each being fluorinated on A and D unit, where quaterthiophene and benzothiadiazole are used as D and A unit, respectively, in order to investigate the effects of fluorination position on photophysical properties of polymers and their device performances of polymer solar cells. Although the fluorination on either D or A unit effectively enhances intermolecular interaction, exhibiting strong vibronic shoulder in UV?Visible absorption spectra, and lowers energy levels, retaining a low bandgap of 1.58 eV, the polymer with fluorinated D unit exhibits a PCE of 7.10%, while the polymer with fluorinated A unit exhibits a PCE of 6.75%. Therefore it can be concluded that the fluorination on D unit in D?A polymer is a very promising method for achieving high performance solar cells.OAIID:oai:osos.snu.ac.kr:snu2014-01/104/0000001236/9SEQ:9PERF_CD:SNU2014-01EVAL_ITEM_CD:104USER_ID:0000001236ADJUST_YN:NEMP_ID:A004558DEPT_CD:445CITE_RATE:0FILENAME:141008추계고분자학회_조제웅.pdfDEPT_NM:재료공학부CONFIRM: