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Photosystem I as a light-sensitive material in solar cells

Sebastian Szewczyk

Abstract

Photosystem I (PSI) is a protein-pigment complex commonly occurring in thylakoid membranes of the organisms performing oxygenic type of photosynthesis: in higher plants, algae and cyanobacteria. The role of PSI is to carry out the light-driven transmembrane electron transfer. Algal and plant PSI complexes are assembled of the core and additional light harvesting complexes (LHCI). Cyanobacterial PSI complexes do not contain any additional antennas, but they exist in the form of trimers. The light can be absorbed through the chlorophyll molecules present in the PSI structure. About 90 of them is localized in the PSI core and form so called core antenna system. The excitation being an effect of the act of absorption is then transported through the antenna system to the reaction center (RC) located at the central part of the structure. RC consists of the system of the electron carriers which use the exaction energy to perform the spatial charge separation. The important feature of the PSI is high quantum efficiency of this process: near the unity. It means, that almost every absorbed photon initiates the charge separation. Therefore, PSI can be considered as a highly efficient, natural opto-electronic converter working in the nanoscale. This feature together with high structural stability of the PSI complex makes the PSI an interesting object for biophotovoltaics. The advantage of the constructions based on photosynthetic complexes is that they are abundant in nature, their isolation cost is low and also they are free of toxicity. Nowadays, many research groups conduct the experiments related to bio-hybrid structures based on PSI complexes. However, an important question arises: how does the new environment (drastically different from the natural one) of the deposited on non-organic surfaces, partially dried and aggregated PSI complexes affect their properties? The main goal of this thesis is an examination of the spectral characteristics and excitation dynamics of the PSI complexes deposited on glass covered with conductive layer (FTO), and comparison these results with those obtained for PSI in solution. The first steps of energy and electron transfer after excitation occurs in picosecond and sub-picosecond time scale. Therefore, in order to study these processes, the time-resolved ultrafast laser spectroscopy techniques were used, both fluorescence and absorption. The PSI complexes deposited onto FTO glass (similar to those used in the spectroscopic measurements) were also examined for the photovoltaic response. In addition, an attempt was made to explain the mechanism responsible for photocurrent generation. The secondary objective of the work was to create a simple and universal procedure for isolation of PSI complexes from three different types of organisms: plants, algae and cyanobacteria. Results obtained from the time-resolved measurements suggest, that excitation dynamics in deposited PSI preserves its bi-exponential character observed for PSI in solution. However, the excitation decay caused by trapping in RC is accelerated [Szewczyk et al. 2017, Photosynthesis Research 132, 111-126]. Deposition of the PSI complexes leads also to slight modification of their spectral properties, originating from additional interactions between chlorophyll molecules under the conditions of dense packing. In order to explain the origin of the acceleration of the excitation decay, the time-resolved transient absorption measurements were performed. Comparison of the experiments in which PSI complexes were deposited on conductive and non-conductive surfaces, and being either dried or in contact with aqueous solution suggests, that the dense packing is the reason of aforementioned acceleration [Szewczyk et al. 2018, Photosynthesis Research 136, 171-181]. The electrochemical measurements indicate, that PSI complexes sustain their photocatalytic activity, manifested by ability to generate photocurrent. The obtained results confirm usefulness of the PSI complexes in bio-photovoltaic constructions, despite of some spectral and dynamic modifications.
Record ID
UAM856c550ee05a4c3280ff3254fe098821
Diploma type
Doctor of Philosophy
Author
Title in Polish
Fotosystem I jako materiał światłoczuły w ogniwach słonecznych
Title in English
Photosystem I as a light-sensitive material in solar cells
Language
pol (pl) Polish
Certifying Unit
Faculty of Physics (SNŚ/WyF/FoP)
Discipline
biophysics / (physical sciences domain) / (physical sciences)
Scientific discipline (2.0)
6.6 physical sciences
Status
Finished
Defense Date
27-09-2018
Title date
27-09-2018
Supervisor
URL
http://hdl.handle.net/10593/23911 Opening in a new tab
Keywords in English
Photosystem I, time-resolved spectroscopy, Energy transfer, red chlorophylls
Abstract in English
Photosystem I (PSI) is a protein-pigment complex commonly occurring in thylakoid membranes of the organisms performing oxygenic type of photosynthesis: in higher plants, algae and cyanobacteria. The role of PSI is to carry out the light-driven transmembrane electron transfer. Algal and plant PSI complexes are assembled of the core and additional light harvesting complexes (LHCI). Cyanobacterial PSI complexes do not contain any additional antennas, but they exist in the form of trimers. The light can be absorbed through the chlorophyll molecules present in the PSI structure. About 90 of them is localized in the PSI core and form so called core antenna system. The excitation being an effect of the act of absorption is then transported through the antenna system to the reaction center (RC) located at the central part of the structure. RC consists of the system of the electron carriers which use the exaction energy to perform the spatial charge separation. The important feature of the PSI is high quantum efficiency of this process: near the unity. It means, that almost every absorbed photon initiates the charge separation. Therefore, PSI can be considered as a highly efficient, natural opto-electronic converter working in the nanoscale. This feature together with high structural stability of the PSI complex makes the PSI an interesting object for biophotovoltaics. The advantage of the constructions based on photosynthetic complexes is that they are abundant in nature, their isolation cost is low and also they are free of toxicity. Nowadays, many research groups conduct the experiments related to bio-hybrid structures based on PSI complexes. However, an important question arises: how does the new environment (drastically different from the natural one) of the deposited on non-organic surfaces, partially dried and aggregated PSI complexes affect their properties? The main goal of this thesis is an examination of the spectral characteristics and excitation dynamics of the PSI complexes deposited on glass covered with conductive layer (FTO), and comparison these results with those obtained for PSI in solution. The first steps of energy and electron transfer after excitation occurs in picosecond and sub-picosecond time scale. Therefore, in order to study these processes, the time-resolved ultrafast laser spectroscopy techniques were used, both fluorescence and absorption. The PSI complexes deposited onto FTO glass (similar to those used in the spectroscopic measurements) were also examined for the photovoltaic response. In addition, an attempt was made to explain the mechanism responsible for photocurrent generation. The secondary objective of the work was to create a simple and universal procedure for isolation of PSI complexes from three different types of organisms: plants, algae and cyanobacteria. Results obtained from the time-resolved measurements suggest, that excitation dynamics in deposited PSI preserves its bi-exponential character observed for PSI in solution. However, the excitation decay caused by trapping in RC is accelerated [Szewczyk et al. 2017, Photosynthesis Research 132, 111-126]. Deposition of the PSI complexes leads also to slight modification of their spectral properties, originating from additional interactions between chlorophyll molecules under the conditions of dense packing. In order to explain the origin of the acceleration of the excitation decay, the time-resolved transient absorption measurements were performed. Comparison of the experiments in which PSI complexes were deposited on conductive and non-conductive surfaces, and being either dried or in contact with aqueous solution suggests, that the dense packing is the reason of aforementioned acceleration [Szewczyk et al. 2018, Photosynthesis Research 136, 171-181]. The electrochemical measurements indicate, that PSI complexes sustain their photocatalytic activity, manifested by ability to generate photocurrent. The obtained results confirm usefulness of the PSI complexes in bio-photovoltaic constructions, despite of some spectral and dynamic modifications.

Uniform Resource Identifier
https://researchportal.amu.edu.pl/info/phd/UAM856c550ee05a4c3280ff3254fe098821/
URN
urn:amu-prod:UAM856c550ee05a4c3280ff3254fe098821

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