Oxygen, Water and Light are the main degradation causing elements. Oxygen and Light: Active material react with oxygen in the presence of light and a photo oxidation reaction occurs. This destroys active material's ability to absorb light and create electrical carriers. Oxygen also reacts with metal electrodes. Aluminium is most popular as electrode but it is more susceptible to degradation. Silver is more stable as compared to aluminium and hence used in stable solar cells. Water : Water may react with both the hole transport layer and the electrodes and cause degradation of solar cell. There are also a number of important physical mechanisms that degrade the solar cell functionality. The active layer is made up of certain components. The size of domains of each component is optimized for exciton transport and charge separation. This junction structure may get destroyed by slow rearrangement of these constituents, and the destruction can be accelerated using heat. The multi-layer structure of polymer solar cell can also delaminate at weak interfaces between the layers, for example, between the hole conductor, PEDOT:PSS and the active layer. Moreover, if the top and bottom electrodes get connected, it may lead to an electrical short. Similar situation can arise during the printing process (we'll come back to this subject in a separate lesson). So the most important factors are oxygen and humidity, sometimes together with light and higher temperatures.

Polymerization is the process of combining many small molecules (the monomers) into a covalently bonded chain or network. Stille cross coupling - The Stille cross coupling reaction can generate new carbon-carbon bonds, through transmetallation of an organotin compound with a halogenide as coupling partner, with the use of a palladium catalyst system in an a solvent. Suzuki cross coupling - This comprises an organoboron functionalized compound together with an organic halide compound and also apply a palladium catalytic system. Direct arylation - This is a Heck-type coupling and compared to Stille and Suzuki reactions the direct arylation polymerization does not require preparation of stannylated or boronated reagents which eliminates one of the normally more complicated steps in the monomer preparation. Source : http://www.plasticphotovoltaics.org/lc/lc-materials/lc-synthesis.html

Like all solar cells, the polymer solar cell converts light into electricity, by converting a flux of photons (light) into a flux of charged particles (a current). This conversion process is made possible by the combination of several types of materials, all having distinct electrical and optical characteristics as described in the layer stack, but most importantly is the inclusion of semiconductors. The layer stack Making a polymer solar cell is often done using polymers dissolved in organic solvents, which are transferred by printing or coating methods to a substrate. The materials are added in layers in a certain order to build a solar cell stack. The materials needed in the solar cell stack are; a central active (light absorbing) layer, which translate the impinging photons into separate electrons and holes, a selective charge transport layer on each side of the active layer, allowing only passage of either electrons (ETL) or holes (HTL), and finally two electrodes for extracting the charges from the solar cell, with at least one of the electrodes having a requirement of transparency such that the light can pass through and reach the active layer. Source : http://www.plasticphotovoltaics.org/lc/lc-polymersolarcells/lc-how.html