Graded-Gap Coatings for Organic Solar Cells
Аннотация
The possibility of using a graded-gap crystal as a protective coating of organic solar cells from harmful chemical and other external influences has been studied. On the basis of a quantum model for an electronic near-surface state with an Airy potential well, an expression is obtained that is radically different from the Tamm level, with the help of which the condition of light transparency of the graded-gap region is formulated, but with the implementation of protective properties due to a reduced band gap. It is assumed that the developed method is valid for both classical semiconductors and ionic materials. It was shown that graded-gap coatings have no electronic levels at a certain thickness and, therefore, do not absorb solar radiation; they are completely transparent and can also be used as encapsulating coatings for organic solar cells. Antireflection coatings based on MgF2–CaF2 composite materials are considered as an example of a graded-gap coating. Composite material MgF2–CaF2 is a homogeneous material with an ionic bond, so the coating based on it has graded-gap properties. Such coatings are antireflective and promising for encapsulation of organic solar cells. The increase in the transmission of a glass substrate with applied antireflection coatings is 1.68–2.27%, depending on the composition of the coating. After storage under normal conditions for 3 years (2018–2020) and climatic tests for 1 year (2021), the coatings retained their spectral–optical properties. The experiment showed that graded-gap coatings on organic solar cells are antireflective and protective from external influences.