Abstract:
Organic photovoltaic has been developed for more than 30 years, however, within the last
decade the research field gained considerable in momentum. The amount of solar energy
lighting up Earth's land mass every year is nearly 3,000 times the total amount of annual human
energy use. But to compete with energy from fossil fuels, photovoltaic devices must convert
sunlight to electricity with a certain measure of efficiency. For polymer-based organic
photovoltaic cells, which are far less expensive to manufacture than silicon-based solar cells,
scientists have long believed that the key to high efficiencies rests in the purity of the
polymer/organic cell's two domains -- acceptor and donor.
The basic principle of organic solar cells is to place layer(s) of organic electronic material
between two metallic conductors of two different work functions. This difference of work
function sets up an electric field within the organic layer(s) which when absorbs light, causes
the excited electrons to be pushed towards positive electrode and holes towards negative
electrode. This thesis has been based on an optimized two-layer organic solar cell which aims
to increase the photon absorption by increasing the interface area between donor and acceptor
levels.
This report summarizes the latest advances in the interfacial layers for bi-layer OSCs (including
bulk hetero-junction photovoltaic cells. Finally, a brief summary and some perspectives about
the current challenges and opportunities have been presented about this interesting area of
research.
Description:
The infancy of organic solar cells began in the late 1950s. At this time, photoconductivity in some organic semiconductor cells were measured with voltage of 1 V by some research groups. They proposed that if a single layer PV cell is illuminated consisting of an organic layer, sandwich cell with low work function metal (aluminum, Al) and a conducting glass of high work function (indium tin oxide, ITO), photoconductivity will be observed. In the 1960s, semiconducting properties were observed in dyes particularly in methylene blue. Efficiency of 10−5 % in sunlight conversion was reported in the early 1970s to an improvement of 1 % in the early 1980s. This was achieved through an interesting phenomenon known as heterojunction. This phenomenon is a surface between semiconducting materials of dissimilar layers. Photovoltaic devices were applied with hetero-junction where donor-acceptor organic cells were tailored together. In recent years, photoconductivity has been measured in dyes and the dye solar cells have progressively been improved for laboratory cells. Currently power conversion efficiency of organic photovoltaic in single-junction devices is over 9 % and that of multi-junction cell is over 12 %.
