Interfacial Charge Transfer in CsPbI3 Perovskite Quantum Dots Restricted; Files Only

Shang, Qiongyi (Summer 2019)

Permanent URL: https://etd.library.emory.edu/concern/etds/wd375x29d?locale=en
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Abstract

CsPbI3 perovskite quantum dots (QDs) are of great interests in their light-harvesting and emitting properties. Notably, CsPbI3 QD solar cell (with a reported efficiency of 13.43% and high stability) is a promising device platform for further improvement. Understanding the charge carrier dynamics in CsPbI3 QDs may provide some relevant insights to develop high-performance photovoltaic devices more rationally. In this dissertation, we put efforts to measure the interfacial charge transfer rates involving CsPbI3 QDs by visible ultrafast transient absorption (TA) spectroscopy.

To resolve the factors that influence charge transfer rates, we studied QD-electron acceptor systems in both solution phase and solid phase. In thin-film solid phase, the photochemical interaction between QDs and metal oxide nanoparticles is directly related to the performance of photovoltaic devices. In solution phase, because nonpolar solvent environment is benign to the QDs, we can reveal the photochemical properties of perovskite QDs more easily.

In solution phase study, we investigated the influence of anion composition and QD size on charge transfer rates in CsPbI3 QD-Rhodamine B (RhB) complex systems. By replacing the iodide partially or fully by bromide, the charge separation (CS) and charge recombination (CR) rates decrease significantly. By decreasing the size of CsPbI3 QDs, the CS and CR rates of QD-RhB complexes increase, which is primarily due to the increase of electronic coupling strength.

In thin-film study, we measured the charge transfer rates between CsPbI3 QDs and metal oxide nanoparticle films by TA and time-resolved photoluminescence (PL) spectroscopy. We found that both the CS and CR rates at QD/TiO2 interface were ~5-10 times faster than those at QD/ZnO interface, suggesting that these processes depend sensitively on the nature of electron extraction layer material. We also measured the CS and CR rates in QD-TiO2 films with QDs treated by different post-synthesis purification methods. With methyl acetate (MeOAc) wash, the CS rate increased while the CR rate decreased, compared to the direct precipitate QDs, indicating that removal of surface ligands using MeOAc wash was beneficial to the performance of CsPbI3 QD solar cells. 

Table of Contents

Chapter 1. Introduction. 1

1.1. Motivation to understand charge transfer dynamics in CsPbI3 QDs. 1

1.2. Factors that influence charge transfer dynamics. 2

1.3. Charge transfer study on CsPbI3 QDs in organic solutions. 5

1.4. Charge transfer study on CsPbI3 QDs in solid films. 6

1.5. Conclusion. 7

Chapter 2. Experimental methods. 8

2.1. Sample preparations. 8

2.1.1. Perovskite QDs and CdSe QDs synthesis in Chapter 3. 8

2.1.2. Sample preparations in chapter 4. 11

2.1.3 Synthesis of CsPbI3 QDs with different sizes in Chapter 5. 13

2.1.4 Sample preparations in Chapter 6. 14

2.1.5 QDs with different post-synthesis treatments in Chapter 7. 16

2.2. Time-resolved spectroscopy. 16

2.2.1. Visible femtosecond transient absorption setup. 16

2.2.2 Visible nanosecond transient absorption setup. 17

2.2.3. Static PL and Time-resolved PL decay measurements. 18

Chapter 3. Effect of residual PbI2 in CsPbI3 QDs. 19

3.1. Introduction. 19

3.2. The influence of QDs size distribution on PLE spectra. 19

3.2.1. PLE measurement without considering the size distribution of QDs. 19

3.2.2. PLE measurement considering the size distribution of QDs. 21

3.3. Influence of PbI2 in CsPbI3 QDs. 22

3.4. Conclusion. 25

Chapter 4. Anion composition dependent charge transfer in CsPbI3 QDs. 26

4.1. Introduction. 26

4.2. Results and discussion. 27

4.2.1. Characterization of perovskite QDs. 27

4.2.2. Electron transfer and charge recombination kinetics in CsPbBr3 QDs. 29

4.2.3. Electron transfer and charge recombination kinetics in CsPbBr0.75I2.25 and CsPbI3 QDs. 32

4.2.4. Hole transfer from CsPbX3 QDs to PTZ.. 35

4.3. Conclusion. 38

Appendix 1. Kinetics fitting in free CsPbX3 QDs. 39

Appendix 2. Kinetics fitting in QD-RhB complexes. 40

Appendix 3. PL decay kinetics fitting in QD-PTZ complexes. 47

Chapter 5. Size dependent charge transfer in CsPbI3 QDs. 50

5.1. Introduction. 50

5.2. Results and discussion. 52

5.2.1. Sample characterizations. 52

5.2.2. TA study of CsPbI3 QD-RhB complexes. 53

5.2.3. Theoretical calculation of charge transfer rates. 58

5.3. Conclusion. 63

Appendix 1. XB kinetics fitting model 65

Chapter 6. Charge transfer at the interface of CsPbI3 QDs and metal oxide layer 69

6.1. Introduction. 69

6.2. Results and discussion. 70

6.2.1. Sample characterizations. 70

6.2.2. TA study of charge transfer in CsPbI3 QD-metal oxide films. 72

6.2.3. Analysis of PL decay and XB kinetics. 73

6.2.4. Implications on perovskite thin-film solar cells. 75

6.3. Conclusion. 76

Appendix 1. Pump power dependent TA measurements. 77

Appendix 2. XB kinetics fitting in QD-Metal oxide NP films. 80

Appendix 3. PL decay kinetics fitting. 85

Chapter 7. Charge transfer study on CsPbI3 QD-TiO2 films and the influence of different post-synthesis treatments. 87

7.1. Introduction. 87

7.2. Results and discussion. 89

7.2.1. Sample characterizations. 89

7.2.2. TA study on QD-TiO2 films. 93

7.2.3. Analysis of PL decay and XB kinetics. 95

7.2.4. Implications on perovskite QD devices. 97

7.3. Conclusion. 98

Appendix 1. FTIR of films adsorbed with ligands. 99

Appendix 2. Electron and hole contribution to XB.. 100

Appendix 3. XB kinetics and PL decay kinetics fitting in QD-Metal oxide NP films. 103

Chapter 8. Summary. 103

References. 109

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