Progress and perspectives in exploiting photosynthetic biomolecules for solar energy harnessing

Abstract

5Photosynthetic proteins are emerging as a new class of photovoltaic materials as their nature-designed architecture and internal circuitry are so sophisticated that they carry out the initial light-driven steps of photosynthesis with ≈ 100% quantum efficiency. Research on bioinspired solar cells has increased in recent years as they promise better efficiency than the conventional p-n junction solar cells that have limited conversion efficiency (34%). Since it is a mammoth task to perfectly mimic the intricate proteins 10 evolved in nature, the idea of interfacing the natural proteins with engineered materials seems propitious for developing biohybrid solar cells. Herein, we summarize various approaches in immobilizing the photosynthetic biomolecules in photovoltaic devices and the progress in the photocurrent generation achieved. This review highlights the multidisciplinary nature of photosynthetic biohybrid devices and their future prospects in light of some of the research challenges and discrepancies witnessed by this field. 15 The fascinating aspect of this research area is that it guides the biologists to explore the possibilities of improving protein stability and robustness suitable for solar cells and inspires the solar cell researchers to explore the physics behind the working mechanisms of biohybrid solar cells which can generate novel architectures in future solar energy conversion devices. 60 superior system and mechanism for light harvesting and energy conversion. Their quantum efficiencies 17 are higher than that of the manmade solar cells. [18][19][20] Photosynthesis is an exemplary model for solar cell research as it is the prime mover powering the biological world, the mechanism behind the energy storage in 65 fossil fuels and the sustainer of earth's oxygenated atmosphere. 21 The architecture and the internal circuitry of the photosynthetic systems are very sophisticated that the initial light driven steps have ≈ 100% quantum efficiency. 18,22,23 Bioinspiration of photosynthesis in solar cells has instigated novel research 70 perspectives which are, in close pace, moving towards devising a high efficiency solar cell. Artificial Photosynthesis is one novel approach that tries to emulate the natural photosynthetic systems REVIEW This journal is © The Royal Society of Chemistry [year] [journal], [year], [vol], 00-00 | 9Fig. 7 (a) Two possible ways of RC binding and ET pathways between RC and electrode. P-primary electron donor (special pair), B-monomeric bacteriochlorophyll, H-bacteriopheophytin, Qa and Qb-primary and secondary electron acceptors (quinones). [Adapted from ref. 81 and ref.34, with permission from Elsevier Ltd] (b) Photoinduced-and dark-electron transfers in RC-Cyt-SAM-Gold electrode [Adapted with permission from ref.82,

Enhanced Output from Biohybrid Photoelectrochemical Transparent Tandem Cells Integrating Photosynthetic Proteins Genetically Modified for Expanded Solar Energy Harvesting

“…[7,11] for reviews). In contrast, there have been almost no attempts to enhance photocurrents by augmenting the natural light-harvesting abilities of photosynthetic bacteria and therefore the spectral range covered in biohybrid devices.…”

“…[5,6] The photosynthetic pigment-proteins of plants, algae, and bacteria have therefore been evaluated for a range of potential optoelectronic, bioelectronic, and photobioelectrochemical devices and applications. [7,8] RCs from purple photosynthetic bacteria such as Rhodobacter (Rba.) sphaeroides, [9] and the larger RC-LH1 complexes they form with the LH1 light harvesting protein, [10] are a popular choice for the construction of photo-bioelectrochemical cells.…”

On the mechanism of ubiquinone mediated photocurrent generation by a reaction center based photocathode

“…Particular attention has been paid to the Photosystem I complex from oxygenic phototrophs [15][16][17] and both the RC and RC/light harvesting complexes from anoxygenic purple photosynthetic bacteria such as Rhodobacter (Rba.) sphaeroides [4][5][6][7][8]10,[18][19][20][21][22][23]. Major preoccupations of this work have been the development of strategies for effective interfacing of the positive and negative terminals of the photovoltaic protein to the working and counter electrode, either through direct binding or the use of diffusional mediators [4][5][6][7][8][16][17][18][19][20][21][22][23][24][25][26][27].…”

“…This provides sufficient time for diffusional processes to remove electrons from the "negative terminal" of the RC and donate electrons to the "positive terminal", resetting the RC for the next turnover. Developments in our understanding of RC mechanism have influenced the design of new synthetic materials for solar energy conversion, and there is interest in the hybridization of both natural and engineered RC proteins with man-made materials for applications in photovoltaics [4][5][6][7][8][9], biosensing [10,11] and molecular electronics [12,13].…”

“…sphaeroides [4][5][6][7][8]10,[18][19][20][21][22][23]. Major preoccupations of this work have been the development of strategies for effective interfacing of the positive and negative terminals of the photovoltaic protein to the working and counter electrode, either through direct binding or the use of diffusional mediators [4][5][6][7][8][16][17][18][19][20][21][22][23][24][25][26][27]. In the case of RC's from purple bacteria a particularly effective strategy has been to use analogues of the natural electron donor and electron acceptor, cytochrome (cyt) c2 and ubiquinone-10 (UQ10), to connect the photovoltaic protein to the two electrodes [18,20,22,[27][28][29].…”