Solar Cells and Optoelectronic Devices in Space

Molecular Orientation and Femtosecond Electron Transfer Dynamics in Halogenated and Nonhalogenated, Eco-Friendly Processed PTB7-Th, ITIC, PTB7-Th:ITIC, and PTB7-Th:PCBM Films

“…Given their properties like easy deposition in flexible substrates and low synthesis cost, the development of organic solar cells (OSCs), the third generation of photovoltaic technology, has been a subject widely explored in the past two decades through the literature. − Efforts to improve this technology made the power conversion efficiency (PCE) values grow from 2.5% (2001) to 18.6% (2020) . These values are strongly dependent on how the components of the active layer of these devices are chosen and processed, as there are many configurations of the cells, − and various donors and acceptors available for the construction of such devices. ,− …”

“…Due to their good solubility in organic solvents, high electron-affinity, effective intermolecular π – π interactions, high electron mobility, and isotropic charge transport, since the earlier development of OSCs until the middle of the last decade, the OSC market had used fullerene derivatives such as PC 61 BM and PC 71 BM as major acceptors units in the active layer, reaching PCE values of 13%. ,, …”

“…Another aspect of fullerene acceptors to be regarded is that they present low absorption coefficient in the visible range, making it difficult to choose a donor system, as the exciton dissociation requires the best alignment in the frontier energy levels (highest occupied molecular orbital (HOMO) and lowest unoccupied molecular orbital (LUMO)) and a bandgap value near the maximum of solar irradiance. ,,,,, …”

“…1,8−14 Due to their good solubility in organic solvents, high electron-affinity, effective intermolecular π−π interactions, high electron mobility, and isotropic charge transport, since the earlier development of OSCs until the middle of the last decade, the OSC market had used fullerene derivatives such as PC 61 BM and PC 71 BM as major acceptors units in the active layer, reaching PCE values of 13%. 1,2,15 However, the mechanism of charge transport to the electrodesthe final step of the photovoltaic process broadly depends on the local morphology of the blend. In opposition to the properties mentioned above, fullerene acceptors show limitations due to their tendency to form clusters, decreasing the rate of charge transport, as first concluded by Collins and co-workers employing different Xray techniques 16 and further extended by Kniepert and coworkers' studies in charge mobility in devices with such acceptors.…”

“…Another aspect of fullerene acceptors to be regarded is that they present low absorption coefficient in the visible range, making it difficult to choose a donor system, as the exciton dissociation requires the best alignment in the frontier energy levels (highest occupied molecular orbital (HOMO) and lowest unoccupied molecular orbital (LUMO)) and a bandgap value near the maximum of solar irradiance. 1,2,11,12,15,18 It is possible to affirm that these two limitations have turned nonfullerene acceptors (NFAs) of great interest in the development of new molecules and polymers as acceptors for the active phase of OSCs. 2,[8][9][10][11][12]14 As pointed out by Gurney and co-workers, polymers and small molecules have more probability of being dispersed than fullerene derivatives, promoting better percolation pathways to the charge carriers from the D/A interface until the electrodes.…”