The open-circuit voltage (V OC ) tuning effect due to the variation of the low concentration of the third component in ternary organic solar cells has been mainly attributed to interfacial phenomena. Up to date, the models reported in the literature to analyze such interfacial phenomena are based on optical characterization. In this work is proposed a different approach to study such a V OC tuning effect by using dark-current characteristics at different temperatures. Specifically, for PTB7-Th:PC 71 BM:ICBA-based solar cells, it is found that an increment of the third component concentration, that is, the fullerene ICBA, causes an increase in the activation energies (E a ) in an Arrhenius-type curve. This, in turn, decreases the reverse saturation current (J 0 ) of the devices, thereby incrementing their V OC .
In physics and engineering, circuit modeling together with simple element models has been used to study concurrent physical phenomena. By using simple calculations, the underlying mechanisms that determine certain patterns can be understood. Here, we present a simple mathematical model to describe the COVID-19 pandemic time evolution. The model accounts for three phases occurring at the same pandemic wave, which are influenced by different mechanisms represented by a linear, an exponential, and a power law term, corresponding to an early stage of the contagious spread, an unconstrained spread, and a power-law increase defined by the effectiveness of the social distancing, respectively. This approach is based on parallel and series natural phenomena occurring in electrical circuits. The generality of the present tool is demonstrated using empirical data of nine countries from different continents.
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