Over the last 12 months, we have witnessed an unexpected breakthrough and rapid evolution in the field of emerging photovoltaics, with the realization of highly efficient solid-state hybrid solar cells based on organometal trihalide perovskite absorbers. In this Perspective, the steps that have led to this discovery are discussed, and the future of this rapidly advancing concept have been considered. It is likely that the next few years of solar research will advance this technology to the very highest efficiencies while retaining the very lowest cost and embodied energy. Provided that the stability of the perovskite-based technology can be proven, we will witness the emergence of a contender for ultimately low-cost solar power.

Perovskites: The Emergence of a New Era for Low-Cost, High-Efficiency Solar Cells

http://nathan.instras.com/documentDB/paper-12.pdf

Applications of functionalized transition metal complexes in photonic and optoelectronic devices

3.1. Fundamental Characterization 6672 3.2. Photocurrent Action Spectroscopy 6673 3.3. Optical Characterization 6673 3.4. Characterization of Electron Transfer 6673 4. Electron Transport in Metal Oxide Films 6674 4.1. Mechanism of Photoinduced Carrier Transport 6674 4.2. Characterization of Diffusion Length 6675 4.3. One-Dimensional (1-D) Transport Architectures 6675 4.4. Electrolyte Interactions 6676 5. Recent Trends in Liquid-Junction Solar Cells 6676 5.1. Dye Sensitized Solar Cells 6677 5.2. Quantum Dot Sensitized Solar Cells 6678 5.3. Carbon Nanostructure Based Photochemical Solar Cells 6679

Beyond Photovoltaics: Semiconductor Nanoarchitectures for Liquid-Junction Solar Cells

▪ Abstract Electron injection at dye-sensitized semiconductors is reviewed. Particular emphasis is placed on theoretical and photoelectrochemical studies of dye-sensitized planar and single-crystal electrodes. The accepted mechanism of electron injection, which was derived from these classical studies, is introduced. Selected photoelectrochemical studies of dye-sensitized nanocrystalline semiconductors are reviewed; emphasis is given to factors that influence the efficiencies of electron injection and charge recombination. The development of quasi-solid-state nanocrystalline dye-sensitized solar cells is also discussed. Recent time-resolved spectroscopic studies of electron injection and charge recombination are reviewed. These studies have led to a better understanding of electron injection mechanisms, and have revealed the limitations of the classical models.

Electron injection at dye-sensitized semiconductor electrodes.

Adsorption of a cationic dye, cresyl violet, on SnO2 and SiO2 nanoclusters and nanocrystalline thin films results in the formation of H-aggregates. These dyes are photochemically and electrochemically active and extend the photoresponse of large bandgap semiconductors such as SnO2. Photocurrent generation in dye capped nanocrystalline films of SnO2 has been demonstrated with visible light excitation. A photon-to-photocurrent generation efficiency around 1% has been observed at 510 nm. Back electron transfer between the photoinjected electron and the oxidized sensitizer plays an important role in controlling the efficiency of net electron transfer. Transient absorption and microwave absorption measurements of the dye aggregate capped SnO2 films suggest that the back electron transfer is multiexponential and most is completed within a few hundred nanoseconds. The activation energy of the back electron transfer process is very low (∼1.7 kJ/mol).

Dye capped semiconductor nanoclusters. role of back electron transfer in the photosensitization of sno2 nanocrystallites with cresyl violet aggregates

Spectral sensitization studies of methylene blue at highly and moderately doped ZnO single crystal electrodes were performed to investigate the origin of the relative low quantum yield of this sensitizer for electron injection. - The low quantum yield can be attributed to a number of effective quenching processes, in which surface states as well as the fast singlet-triplet conversion and the photoreduction of methylene blue are involved.



Untersuchungen zur spektralen Sensibilisierung an hoch- und masig dotierten ZnO-Einkristall-Elektroden mittels Methylenblau wurden unternommen, um die Ursache der relativ niedrigen Quantenausbeute dieses Sensibilisators aufzuklaren. - Die geringe Quantenausbeute wird als Folge einer Reihe effektiver Loschprozesse gedeutet. Dabei spielen Oberflachenzustande, aber auch die bekanntermasen schnelle Singlett-Triplett-Konversion und eventuell auch die Photoreduktion der Methylenblau-Molekule eine wesentliche Rolle.

Spectral Sensitization of ZnO‐Electrodes by Methylene Blue

The sensitization photocurrent at single crystalline ZnO electrodes in contact with an aqueous solution of crystal violet has been investigated during excitation by a 1 msec laser pulse. The photocurrent shows relaxation phenomena which can be explained by an involvement of “surface states. They capture electrons from the excited dye molecules followed by electron injection into the conduction band or recombination” with the oxidized dye molecules. – The quantum yield for the electron injection is in the order of 2%. This relatively low value a high efficiency of the recombination via surface states. – In the presence of hydroquinone, a slight increase of the quantum observed which is attributed to a photoreduction of the excited dye molecules. The reduced crystal violet molecule can inject an electron into the conduction band from its ground state.



Es wurden sensibilisierte Photostrome an einkristallinen ZnO-Elektroden im Kontakt mit wasrigen, Kristallviolett enthaltenden Elektro. Die Photostrome wahrend eines Laser-Lichtpulses von 1 msec Dauer zeigen Relaxationserscheinungen. Diese werden Einfang von Elektronen aus angeregten Farbstoffmolekulen in Oberflachenzustanden mit anschliesender Injektion dieser Elektronen in das Letiungsband oder Rekombination mit den oxidierten Molekulen erklart. – Die Quantenausbeute fur Elektroneninjektionen der Grosenordnung von 2%. Das deutet auf eine sehr grose Effektivitat der Rekombination uber Oberflachenzustande hin. – von Hydrochinon wird ein geringer Anstieg der Quantenausbeute beobachtet. Dies wird einer Photoreduktion der an Farbstoffmolekule zugeschrieben, wobei angenommen wird, das das reduzierte Kristallviolett-Molekul direkt ein Elektron in das Leitungsband injizieren kann.

T. Yamase

Papers

Spectral Sensitization of ZnO‐Electrodes by Methylene Blue

Involvement of Surface States in the Spectral Sensitization of Zinc Oxide Electrodes

Involvement of surface states in the spectral sensitization of zinc oxide electrodes