User:Minihaa/Materials of organic solar cells

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 * The following paragraph may be merged with Organic solar cell
 * All figures need to be transferred.

Introduction
In bulk heterojunction organic solar cells, the process of converting sunlight into electricity involves four key steps:[20,21]


 * 1) Light is absorbed by the active layer of the solar cell, leading to the creation of excitons (pairs of electrons and holes).
 * 2) The excitons then diffuse to the junctions (interfaces between the donor and acceptor materials).
 * 3) At the junctions, the excitons dissociate into separate charges, creating germinate pairs (electron-hole pairs).
 * 4) The charges separates, move through the material and are collected by electrodes, generating an electric current.

There are two main pathways through which excitons can form and dissociate (see figure). In one pathway (known as channel I), the exciton forms in the donor material, followed by electron transfer to the acceptor material. In the other pathway (channel II), the exciton forms in the acceptor material, followed by electron transfer to the donor material. The dominance of each pathway depends on the absorption properties of the acceptor material used in the organic solar cell. In fullerene-based organic solar cells, channel I dominates the generation of photocurrent. In non-fullerene organic solar cells, both channel I and channel II contribute to the generation of photocurrent.