Charge-transfer states in photosynthesis and organic solar cells

Abstract

Light-induced charge-transfer mechanisms are at the heart of both photosynthesis and photovoltaics. The underlying photophysical mechanisms occurring within photosynthesis and organic photovoltaics in particular show striking similarities. However, they are studied by distinct research communities, often using different terminology. This contribution aims to provide an introductory review and comparison of the light-induced charge-transfer mechanisms occurring in natural photosynthesis and synthetic organic photovoltaics, with a particular focus on the role of so-called charge-transfer complexes characterized by an excited state in which there is charge-transfer from an electron-donating to an electron-accepting molecular entity. From light absorption to fully separated charges, it is important to understand how a charge-transfer complex is excited, forming a charge-transfer state, which can decay to the ground state or provide free charge carries in the case of photovoltaics, or radicals for photochemistry in photosynthetic complexes. Our motivation originates from an ambiguity in the interpretation of charge-transfer states. This review attempts to standardize terminology between both research fields with the general aim of initiating a cross-fertilization between the insights and methodologies of these two worlds regarding the role of charge-transfer complexes, inspiring the cross-disciplinary development of next-generation solar cells. Likewise, we hope to encourage photosynthesis researchers to collaborate with the photovoltaics field, thereby gaining further knowledge of the charge-transfer process in natural light-harvesting systems.

White light emission from helically stacked humin-mimic based H-aggregates in heteroatom free carbon dots

“…In such ordered molecular assemblies, the excitons or charge transfer (CT) states, emerging with delocalized electronic states of electron-hole pairs and bonded by electrostatic force on the same molecule, drastically change the course of energy dissipation channels. 58,59 However, in the vicinity of another molecule with a greater electron affinity-referred to as the electron acceptor (A)charge transfer might occur through diffusion, in which case the electron jumps to A, while the hole stays behind on the socalled electron-donor (D), 60 and this configuration is called CT states. 61 To decisively examine the self-assembly pattern of the Prasanta Kumar Datta is a senior professor at the Department of Physics, Indian Institute of Technology, Kharagpur, India.…”

Excited States by Coupling Piris Natural Orbital Functionals with the Extended Random-Phase Approximation

“…Excited states , are important for the description of photochemical and electrochemical processes, fluorescence and phosphorescence phenomena, spectroscopy, and chemical reaction mechanisms, , with a variety of cutting-edge chemical applications such as the development of new materials for organic solar cells and batteries. − The energy of these states can be calculated using the configuration interaction (CI) method; however, this becomes too expensive even for low levels of CI, although some variations have been developed to address this issue . There are other electronic structure tools that allow studying excited species at a more affordable cost, such as the equation-of-motion coupled-cluster (EOM-CC) − approach, the time-dependent density functional theory (TD-DFT), and the random-phase approximation, but the accuracy achieved is not as good as desired and the picture becomes more complex when it comes to static correlation, since multireference methods are required. , …”

“…Excited states 1 , 2 are important for the description of photochemical 3 and electrochemical processes, 4 fluorescence and phosphorescence phenomena, 5 spectroscopy, 6 and chemical reaction mechanisms, 7 , 8 with a variety of cutting-edge chemical applications such as the development of new materials for organic solar cells 9 and batteries. 10 − 12 The energy of these states can be calculated using the configuration interaction (CI) method; however, this becomes too expensive even for low levels of CI, although some variations have been developed to address this issue.…”