Effects of electric field and temperature on the shape of chlorophyll aggregates in casting films

Chlorophylls in thin-film photovoltaic cells, a critical review

“…ambient humidity or matrix type, 5,14,22,31,38,39 but most importantlyon the aggregation of molecules. 4,[9][10][11][12]21,27,32,34,38,[40][41][42][43][44][45][46][47][48][49] The optical spectroscopy, due to convenience of use and availability in laboratories, serves as the most frequently applied tool for assessing the aggregation state of chlorophylls in solutions and lms.…”

“…In thin solid lms grown on the substrates the Chl aggregates also form fractal structures that can easily be observed using the optical microscopy. 9,10,44,55 Such freedom, or lability of solution-mediated intermolecular interactions, manifested itself in the competition of kinetically and thermodynamically controlled pathways of selfassembling in the water solutions of inherently chiral Zn chlorin derivative with a bulky side substituent. 45 A thermodynamically-driven pathway yields stable, extended 1D helical bers consisting of extended J-aggregates.…”

“…For instance, morphology of the thin lms of Chl aggregates depends on the application of DC voltage during the casting from the water solution. 44 The sensitivity of a supramolecular organization to the deposition conditions reduces the reproducibility of the results and has thus to be minimized by choosing molecular structures having an invariant route of assembly.…”

“…73 The surface of thin lms of various chlorophyll derivatives was examined using AFM/STM and/or SEM techniques in ref. 4,5,12,27,32,[40][41][42][43][44]52, 64 and 73. However, the published gures cannot provide sufficient insight into the lm morphology and usually serve as supplementary experimental facts in the description of samples.…”

“…The vast majority of experiments available in literature refers to the heating cycles in a relatively narrow interval of temperatures, ranging from RT to 60-90 C. Elevated temperatures provoke several undesired, and oen instrumentally uncontrolled, processes such as sintering, decomposition or loss of structural water in the aggregates, thin lms and bulky crystals of chlorophylls. [9][10][11]23,39,44,69,71,72,75,79 This, in turn, leads to uncertainty and possible misinterpretation of the electrical conduction mechanisms by different authors since the parameters can be calculated or compared adequately only when the samples are chemically and structurally equivalent. Looking to the future, we fear that the (photo-)thermal stability issues will dominate the other when developing the PVC devices based on chlorophylls, as it happened with the hybrid perovskites in 2010s.…”