Organic Photovoltaics
Introduction
Organic photovoltaics (OPVs) are a type of photovoltaic system that use organic electronics, a branch of electronics that deals with conductive organic polymers or small organic molecules, for light absorption and charge transport to produce electricity from sunlight by the photovoltaic effect. The organic nature of the materials used in OPVs offers the potential for low-cost, lightweight, and flexible photovoltaic cells.
History
The field of organic photovoltaics has developed rapidly over the past few decades. The first organic photovoltaic cells were made of single molecules that were sandwiched between two electrodes. However, these early devices had very low efficiencies. The discovery of conductive polymers in the 1970s opened up new possibilities for OPVs. The first significant boost in efficiency came in the 1980s with the introduction of bilayer cells.
Working Principle
The working principle of an organic photovoltaic cell involves the excitation of an electron from the highest occupied molecular orbital (HOMO) to the lowest unoccupied molecular orbital (LUMO) of an organic molecule or polymer by absorption of light, creating an exciton, a bound state of an electron and an electron hole which are attracted to each other by the electrostatic Coulomb force.
Materials
The choice of materials in an OPV determines its efficiency, stability, and cost. The active layer of an OPV is typically composed of a blend of a donor and an acceptor material. The donor material is an electron donor which is usually a conjugated polymer, while the acceptor material is an electron acceptor which is usually a fullerene derivative.
Device Architecture
There are two main types of device architectures in organic photovoltaics: the traditional bilayer architecture and the more modern bulk heterojunction (BHJ) architecture. The BHJ architecture has been shown to be more efficient due to its greater interface area between the donor and acceptor materials.
Efficiency and Stability
The efficiency of organic photovoltaic cells is currently lower than that of inorganic photovoltaic cells. However, the gap is closing as new materials and device architectures are developed. Stability is another important factor for OPVs. While OPVs are not as stable as inorganic photovoltaic cells, significant progress has been made in improving the stability of OPVs.
Applications
The potential applications of organic photovoltaics are vast. They can be used in building-integrated photovoltaics, portable power generation, and even in wearable electronics due to their flexibility. The low cost and ease of fabrication of OPVs also make them suitable for use in developing countries where access to electricity is limited.
Future Directions
The future of organic photovoltaics looks promising. With ongoing research and development, the efficiency and stability of OPVs are expected to improve, making them a viable alternative to inorganic photovoltaic cells. The development of new materials and device architectures will also play a crucial role in the advancement of OPVs.