Limit Of Power Conversion Efficiency Research Articles

Cadmium ion soaking treatment for solution processed CuInS xSe 2− x solar cells and its effect on defect properties

Recombination of charge carriers due to electronically active material defects is one of the major factors limiting power conversion efficiency in solar cells. We have studied the defect behavior in CuInS x Se 2− x solar cells fabricated through a solution process with a maximum heating temperature of 390 °C. By introducing a cadmium ion soaking step into the fabrication process, we find that the recombination rate can be reduced. Through the use of capacitance–voltage ( C– V) profiling, drive level capacitance profiling (DLCP) and admittance spectroscopy analysis, the cadmium ion soaking process was found to increase the charge carrier concentration in the bulk of the absorber, and shift the energy level of the N1 defect toward the valence band edge. The soaking process was found to most obviously affect the open circuit voltage with an average improvement of 33 mV.

Enhancement of photovoltaic performance using hybrid CdS nanorods and MEH-PPV active layer in ITO/TiO 2/MEH-PPV:CdS/Au devices

Polymer-based solar cells offer many advantages for cell fabrication such as low-cost roll-to-roll production, large area and flexibility. In this study, the effect of blending cadmium sulfide (CdS) nanorods in poly(2-methoxy-5-(2′-ethylhexyloxy)- p-phenylene vinylene) (MEH-PPV) active layer of ITO/TiO 2/MEH-PPV/Au heterojunction devices on the photovoltaic performance was investigated. The ITO/TiO 2/MEH-PPV:CdS blend/Au solar cells were fabricated using nano-porous titanium dioxide (TiO 2) layer infiltrated with a blend of the MEH-PPV and CdS nanorods to form an active layer for the solar cells. The MEH-PPV layer is known to be an electron donor and a hole transport material. Schottky diode ITO/MEH-PPV/Al devices have a limited power conversion efficiency so the modified ITO/TiO 2/MEH-PPV:CdS blend/Au ohmic heterojunction devices were fabricated. Improvement of photocurrent density, fill factor and power conversion efficiency were demonstrated. These improvements were expected to be a result of a more stable depletion region at the TiO 2/MEH-PPV interface. Moreover the mixing of the CdS nanorods in the MEH-PPV layer improved electron transport in the conjugated polymer MEH-PPV film areas that were disconnected between the conjugated polymer and the TiO 2 film.

Dark carrier recombination in organic solar cell

The carrier recombination in organic solar cells is investigated by numerical modeling to understand the weak dependence of the open-circuit voltage on the workfunction of the electrodes. In Ohmic contact structures, photocarriers recombine predominantly with dark carriers diffused from the electrode into the semiconductor. Such dark carrier recombination becomes the main limit of power conversion efficiency and open-circuit voltage. For a given semiconductor decreasing the workfunction difference of the electrodes reduces simultaneously the dark carrier recombination and the flat band voltage. The balance between these two opposite factors gives a nearly constant open-circuit voltage. In an ideal bilayer structure there is no dark carrier recombination and the efficiency is demonstrated to be 60% higher than single layer blend.

A molecular approach to the intermediate band solar cell: The symmetric case

Molecular materials may overcome some of the difficulties for making an intermediate band solar cell by storing energy in long-lived triplet states. Both the problems of fast nonradiative interband relaxation and selective photon absorption can be solved by this approach. A practical implementation of the molecular intermediate band solar cell is considered with a symmetric band alignment, resting on a proven triplet-triplet annihilation process. The limiting power conversion efficiency for this system exceeds that of a single bandgap device over a broad range, peaking at 40.6% for 1.9eV under 1 sun illumination.

A brief history of the development of organic and polymeric photovoltaics

In this paper an overview of the development of organic photovoltaics is given, with emphasis on polymer-based solar cells. The observation of photoconductivity in solid anthracene in the beginning of the 19th century marked the start of this field. The first real investigations of photovoltaic (PV) devices came in the 1950s, where a number of organic dyes, particularly chlorophyll and related compounds, were studied. In the 1980s the first polymers (including poly(sulphur nitride) and polyacetylene) were investigated in PV cells. However, simple PV devices based on dyes or polymers yield limited power conversion efficiencies (PCE), typically well below 0.1%. A major breakthrough came in 1986 when Tang discovered that bringing a donor and an acceptor together in one cell could dramatically increase the PCE to 1%. This concept of heterojunction has since been widely exploited in a number of donor–acceptor cells, including dye/dye, polymer/dye, polymer/polymer and polymer/fullerene blends. Due to the high electron affinity of fullerene, polymer/fullerene blends have been subject to particular investigation during the past decade. Earlier problems in obtaining efficient charge carrier separation have been overcome and PCE of more than 3% have been reported. Different strategies have been used to gain better control over the morphology and further improve efficiency. Among these, covalent attachment of fullerenes to the polymer backbone, creating so-called double-cable polymers, is the latest. The improved PCE of plastic solar cells combined with increased (shelf and operating) lifetime, superior material properties and available manufacturing techniques may push plastic PVs to the market place within a few years.

A brief history of the development of organic and polymeric photovoltaics

Abstract In this paper an overview of the development of organic photovoltaics is given, with emphasis on polymer-based solar cells. The observation of photoconductivity in solid anthracene in the beginning of the 19th century marked the start of this field. The first real investigations of photovoltaic (PV) devices came in the 1950s, where a number of organic dyes, particularly chlorophyll and related compounds, were studied. In the 1980s the first polymers (including poly(sulphur nitride) and polyacetylene) were investigated in PV cells. However, simple PV devices based on dyes or polymers yield limited power conversion efficiencies (PCE), typically well below 0.1%. A major breakthrough came in 1986 when Tang discovered that bringing a donor and an acceptor together in one cell could dramatically increase the PCE to 1%. This concept of heterojunction has since been widely exploited in a number of donor–acceptor cells, including dye/dye, polymer/dye, polymer/polymer and polymer/fullerene blends. Due to the high electron affinity of fullerene, polymer/fullerene blends have been subject to particular investigation during the past decade. Earlier problems in obtaining efficient charge carrier separation have been overcome and PCE of more than 3% have been reported. Different strategies have been used to gain better control over the morphology and further improve efficiency. Among these, covalent attachment of fullerenes to the polymer backbone, creating so-called double-cable polymers, is the latest. The improved PCE of plastic solar cells combined with increased (shelf and operating) lifetime, superior material properties and available manufacturing techniques may push plastic PVs to the market place within a few years.