Emerging Strategies to Reduce Transmission and Thermalization Losses in Solar Cells: Redefining the Limits of Solar Power Conversion Efficiency

Preface
Contents
1 Introduction: Solar Cell Efficiency and Routes Beyond Current Limits
	References
Part I Addressing Transmission Losses: Sequential Absorption via Triplet Fusion in Organic Materials
	2 Photophysics
		2.1 Original Experimental Observations of Delayed Fluorescence in Solution
		2.2 The Mechanism of TTA-UC
		2.3 Requirements for TTA-UC
			Chromophores and Energetic Requirements
			Rules That Govern ISC
			Energy Transfer Mechanisms: Förster and Dexter
			Spin Statistics of TTA
		2.4 The Importance of Kinetics
			Stern-Volmer Analysis
			TTET Rate Constants
			TTA Rate Constants
		2.5 Quadratic-to-Linear Power Dependence
		2.6 Heteromolecular vs. Homomolecular TTA
		2.7 Conclusions
		References
	3 Near-Infrared-to-Visible Photon Upconversion
		3.1 Introduction
		3.2 Semiconductor Nanocrystals as Triplet Sensitizers
		3.3 Triplet Sensitization with Lead Halide Perovskites
		3.4 Molecular Sensitizers Showing a Singlet-to-Triplet Direct Transition
		3.5 Conclusion and Outlook
		References
	4 Photon Upconversion Based on Sensitized Triplet-Triplet Annihilation (sTTA) in Solids
		4.1 Diffusion-Limited sTTA-UC
		4.2 Solution-Mimicking sTTA-UC Materials
		4.3 sTTA in the Solid State
		4.4 Kinetics of Confined sTTA-UC in Nanostructured Solids and Nanomaterials
		4.5 General Remarks
		References
	5 Organic Triplet Photosensitizers for Triplet-Triplet Annihilation Upconversion
		5.1 Introduction
			Brief Introduction of Upconversion Mechanisms
		5.2 Triplet-Triplet Annihilation Upconversion
			Principle of TTA Upconversion
		5.3 Organic Triplet Photosensitizers for TTA Upconversion
			Heavy Atom-Based Triplet Photosensitizers (Metal Atom-Free)
				Iodo-Substituted Triplet Photosensitizers
			Bromo-Substituted Triplet Photosensitizers
			Heavy Atom-Free Triplet Photosensitizers
				Exciton Coupling-Induced ISC
				Use of Electron Spin Converter to Attain Efficient ISC: Application in TTA Upconversion
			Charge Transfer-Induced ISC and the Related Triplet Photosensitizer for TTA Upconversion
			To Increase the Anti-Stokes Shift of TTA Upconversion with Triplet PSs Showing CT Absorption Band and TADF Property
			Triplet PSs Showing S0 =→ T1 Absorption Band for Upconversion
		5.4 General Summary
		References
	6 Plasmon-Enhanced Homogeneous and Heterogeneous Triplet-Triplet Annihilation
		References
Part II Molecular Oxygen and Triplets: Photophysics and Protective Strategies
	7 Molecular Oxygen in Photoresponsive Organic Materials
		7.1 Introduction
			The Cast of Characters
		7.2 Relevant Electronic States of Oxygen
			The Triplet Ground State of Oxygen
			The First Excited Singlet State of Oxygen
			The Second Excited Singlet State of Oxygen
		7.3 Singlet Oxygen Production
			Photosensitized Production
			Optical Transitions in Oxygen
			M-O2 Charge-Transfer Absorption
			Chemical Generation
		7.4 Singlet Oxygen Reactions
		7.5 Nonreactive Deactivation of Singlet Oxygen
		7.6 Singlet Oxygen as a Diffusible Reagent
		7.7 Detecting and Monitoring the Behavior of Singlet Oxygen
			Singlet Oxygen Phosphorescence
			Fluorescent Probes for Singlet Oxygen
			Characterizing Reaction Products
			Judicious Use of Additives and Isotope Effects
		7.8 Mitigating Degradation Mediated by Singlet Oxygen in Photoresponsive Materials
			Molecular Modification of the Photoresponsive Material
			Exploiting the Benefits of an Added Quencher or Antioxidant
			Exploiting the Benefits of Phase Separation and Molecular Confinement
		7.9 Other ROS and the Superoxide Radical Anion
		7.10 Summary and Conclusions
		References
	8 Protective Strategies Toward Long-Term Operation of Annihilation Photon Energy Upconversion
		8.1 Selection Criteria for Singlet Oxygen Protection Efficiency
			The Quantum Yield of the TTA-UC
			Rise Time of the TTA-UC
		8.2 Sacrificial Singlet Oxygen Scavengers (SSOS)
			SSOS Selection Criteria
		References
	9 Additive-Assisted Stabilization Against Photooxidation of Organic and Hybrid Solar Cells
		9.1 Organic Solar Cells
		9.2 Perovskite Solar Cells
		References
Part III Implementation of Photochemical Upconversion in Solar Cells
	10 Optically Coupled Upconversion Solar Cells
		10.1 The Solar Spectrum
			Blackbody Radiation
			Optical Properties of the Atmosphere
			Reflective Concentration
			Luminescent Concentration
		10.2 Attenuation of Sunlight by Solar Cells
			Tauc Model of Semiconductor Absorption
			Experimental Determination
		10.3 The Beer-Lambert Law
			Exponential Decay
			Importance to Efficiency
		10.4 Scattering
		References
	11 Electronically Coupled TTA-UC Solar Cells
		11.1 Introduction
		11.2 Dye-Sensitized TTA-UC Solar Cells
			Introduction
			TTA-UC at Dye-Metal Oxide Interfaces
			Heterogeneous Sensitization
			Metal Ion-Linked Multilayers
				The Metal Ion-Linked Multilayer Prototype
				Molecular Structure-Performance Relationships
				Beyond Bilayers
			Surface-Supported Metal-Organic Frameworks
			Co-deposition
			Organic-Inorganic Hybrid Multilayer
		11.3 Layered Heterojunction TTA-UC Solar Cells
		11.4 Comparing Optical and Electronic Coupling Schemes
		11.5 Conclusion
		References
Part IV Addressing Transmission Losses: Sequential Absorption in Rare Earth Ions
	12 Rare-Earth Ion-Based Photon Up-Conversion for Transmission-Loss Reduction in Solar Cells
		12.1 Introduction
		12.2 Photophysics of RE Ion-Based UC
			Principle
			Lanthanide Ions
			Main Up-Conversion Mechanisms
		12.3 Principal Factors and Strategies to Enhance UC
			Luminescent Centers
			Dopant Concentration Control
			Host Lattice
			Core-Shell Structure Strategies
			Plasmonic Enhancement and Other External Resonators
			Transition Metal Ions Tuned and Sensitized UC
			Optimizing the Excitation Schemes
		12.4 Implementation in Solar Cells
			Silicon Solar Cells
			Dye-Sensitized Solar Cells
			Organic Solar Cells
			Perovskite Solar Cells
		12.5 Conclusions
		References
	13 Nanophotonics for Photon Upconversion Enhancement
		13.1 Introduction
		13.2 Fundamentals of Light-Matter Interaction
		13.3 Energy Transfer Upconversion
		13.4 Photonic Enhancement of Upconversion
		13.5 Current Status and Outlook
		References
Part V Addressing Thermalisation Losses: Singlet Fission and Quantum Cutting
	14 Singlet Fission: Mechanisms and Molecular Design
		14.1 Photophysics of Organic Semiconductors
			Electrons, Excitons, and Spin
		14.2 Singlet Fission
			Triplet-Pair Formation
			Triplet-Pair Dissociation and Recombination
		14.3 Materials for Singlet Fission
			Acenes
			Biradicaloid Molecules
			Dimers and Oligomers
			Next-Generation Singlet Fission Molecules
		14.4 Outlook
		References
	15 Singlet Fission Solar Cells
		15.1 Introduction
		15.2 The Single-Junction Efficiency Limit
		15.3 Tandem Solar Cells
			Efficiency Potential of Tandem Solar Cells
		15.4 Upconversion Solar Cells
		15.5 Downconversion Solar Cells
			MEG
				Efficiency Potential of MEG Solar Cells
				MEG Solar Cells
			Quantum Cutting
				Efficiency Potential of Quantum Cutting Solar Cells
				Quantum Cutting Solar Cells
		15.6 Singlet Fission Solar Cells
			How to Harvest Triplet Energy for a Silicon Solar Cell
				Charge Transfer at the Tetracene/c-Si Interface
				Förster Energy Transfer (FRET) via a Quantum Dot Interlayer
				Radiative Transfer: The “Photon Multiplier”
				Dexter Energy Transfer via Surface Functionalization
			Efficiency Limit of Singlet Fission Solar Cells
		15.7 Perspective on Downconversion and Tandem Solar Cells
		References
Index