چكيده به لاتين
In recent years of solar cell technology, the mechanism of biological cells based on the photosystem I (PSI) nanostructured protein complex have been specially studied. However, the low efficiency of these cells has limited the use of such material in the architecture of photovoltaic cells.While such membrane protein, participating in the z photosynthesis scheme in plants, algae and some bacteria is known as an environmentally friendly natural photodiode without producing harmful wastes. The ability to absorb 47-56% of the photon energy of light with a quantum efficiency of 100 % and the production of free charge carriers with approximately 1 volt potential difference is reported.The natural abundance of photosystem I, with its perfect nanometer dimensions containing two electron donor-acceptor components, could be a good option for use as an active layer in inexpensive solar cell technology. In this thesis, with a deeper insight on the structure and mechanism of such macromolecular complex, possible physical and chemical techniques have been investigatedto improve the function of the protein active layer and optimize the biological solar cell performance.
In the first step, according to the dipole structure of such protein-pigment complex and the feasibility for optimal arrangement and orientation of PSI dipoles in a multilayer deposition, the physical technique of external electric field treatment was employed by maintaining the temperature and life conditionsof these biological macromolecules.Using an almost uniform electric field between the plates of a flat capacitor has been performed the necessary optimizations through investigating the effect of field parameters including field type (pulse-continuous), field strength (bias voltage), duration of applied field and bias direction on the cell functional parameters compared to the control sample. The results showed that the enhancement of cell functional parameters can be achieved due to the alignment of the PSI dipole momentum vectors in field direction. In addition, the results showed that by controlling the pulsed field strength, the photosystem I nano-structure can act as an active layer in order to product the efficient output current up to 40 Am-2. By examining the temporal behavior of cells under external field action, it is possible to estimate the optimal time required to rotate and change the direction of these dipoles at a normal low rotation rate in line with the direction of the applied field. The results showed that with increasing the bias voltages to 400 V, the favorable arrangement probability occurs at an optimal bias width of 60 seconds. It was also shown that by changing the bias direction, cell function can be undergone measurable changes.
In the next step, to improve the active layer and ultimately cell efficiency, increasing the amount of light absorption and stability of this natural photodiode was considered.Hence, the chemical technique called pegylation has been employed by attaching a special polymer (polyethylene glycol) to the PSI protein complex through selecting a functional group (orthoperidyl disulfide) compatible with the structure of photosystem I. such a approach has exploited from the site of cysteine residues and PSI free sulfhydryls.Due to structural modifications, the molar absorption coefficient of the complex increased significantly. Good agreement between the results of various structural analyzes after the pegylation process and acceptable structural improvement relative to the intact protein, was indicating the success of photosystem I protein conjugation. Such structural modification of the protein active layer promised to improve the performance of the final photovoltaic cell.The results confirmed that in the presence of pegylated protein, by increasing the crystalline degree and strengthening the molar absorption coefficient, a significant improvement in the functional parameter of the designed cell was observed.Also, by increasing the concentration of native photosystem I protein in the extraction process, we were able to record better results for pegylated proteins with a fixed polymer peg chain length but at a higher concentration. Finally, to validate the experimental results obtained with the electric field treatments, we performed numerical studies using the SCAPS simulation program, which showed acceptable compatibility with the experimental results.In the Novelty phase, parametric studies have been performed and optimal ranges have been reported to further optimize cells in structures using suitable hole-transporting layers.
Keywords: Photosystem I protein complex, Electrical dipole structure, Pulsed external electric field, Pegylation, SCAPS simulation.
