Organic solar cells active layer

A key focus of research into organic solar cells over the past decade has been the design of materials and devices to increase light absorption in the active layers. These efforts include the development of novel materials, the implementation of clever optics in the device structure to maximise the absorption of incident light, and new fabrication processes and surface modifications to maximise light harvesting. 

A number of approaches are being pursued to modify the electrodes in organic solar cells in order to improve conductivity, selectivity, stability or cost. These include new electrode materials, changes in device processing and additional electrode sub-layers. Most studies have been carried out using the leading material combination, P3HT PCBM, as the active layer. 

Fig. 8.11 The early study on organic solar cell where active layer contains liquid crystalline phthalocyanine as p-type of semiconductor. This is not a BHJ active layer, but of p-i-n junction...

As the active layer of organic solar cells is typically processed from solution, morphology is mainly determined by interactions between the used semiconductor... 

T. L. Benanti, D. Venkataraman, Organic solar cells an overview focusing on active layer morphology, Photo-synth. Res., 87, 73-81 (2006). 

Working principles of organic solar cells are well described in a recent review and some monographs. More or less all types of organic solar cells described above comprise two components in the photoactive layer. One component serves as electron donor, whereas the other works as electron acceptor. Absorption of photons by the active layer components results in the electron transfer from donor to acceptor. This process called photoinduced charge transfer is a fundamental principle of operation of all known organic photovoltaic devices as well as the natural photosynthetic systems. In many cases, donor material is capable of efficient p-type transport and therefore can be called as p-type organic semiconductor. At the same time, electron acceptor material is denoted as n-type semiconductor in many cases. 

Hou J, Guo X (2013) Active layer materials for organic solar cells. Materials and device physics. In Choy WCH (ed) organic solar cells. Springer, London, pp 17-42... 

There are two main types of PSCs including bilayer heterojunction and bulk-heterojunction [7]. Bulk-heterojunction PSCs are more attractive due to their high surface area junction that increases conversion efficiency. This type of polymer solar cell consists of Glass, ITO, PEDOT PSS, active layer, calciiun and aluminum in which conjugated polymer are used as active layer [8]. The organic solar cells with maximum conversion efficiency about 6% still are at the begiiming of development and have a long... 

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