G.D. Sharma

Bio: G.D. Sharma is an academic researcher from Jaipur Engineering College. The author has contributed to research in topics: Polymer solar cell & Schottky barrier. The author has an hindex of 29, co-authored 50 publications receiving 2117 citations. Previous affiliations of G.D. Sharma include Jai Narain Vyas University & Rutgers University.

A Simple and Effective Modification of PCBM for Use as an Electron Acceptor in Efficient Bulk Heterojunction Solar Cells

Abstract: [6,6]-phenyl-C-61-butyric acid methyl ester (PCBM) and poly(3-hexylthiophene) (P3HT) are the most widely used acceptor and donor materials, respectively, in polymer solar cells (PSCs). However, the low LUMO (lowest unoccupied molecular orbital) energy level of PCBM limits the open circuit voltage (Voc) of the PSCs based on P3HT. Herein a simple, low-cost and effective approach of modifying PCBM and improving its absorption is reported which can be extended to all fullerene derivatives with an ester structure. In particular, PCBM is hydrolyzed to carboxylic acid and then converted to the corresponding carbonyl chloride. The latter is condensed with 4-nitro-4’-hydroxy-α-cyanostilbene to afford the modified fullerene F. It is more soluble than PCBM in common organic solvents due to the increase of the organic moiety. Both solutions and thin films of F show stronger absorption than PCBM in the range of 250–900 nm. The electrochemical properties and electronic energy levels of F and PCBM are measured by cyclic voltammetry. The LUMO energy level of F is 0.25 eV higher than that of PCBM. The PSCs based on P3HT with F as an acceptor shows a higher Voc of 0.86 V and a short circuit current (Jsc) of 8.5 mA cm−2, resulting in a power conversion efficiency (PCE) of 4.23%, while the PSC based on P3HT:PCBM shows a PCE of about 2.93% under the same conditions. The results indicate that the modified PCBM, i.e., F, is an excellent acceptor for PSC based on bulk heterojunction active layers. A maximum overall PCE of 5.25% is achieved with the PSC based on the P3HT:F blend deposited from a mixture of solvents (chloroform/acetone) and subsequent thermal annealing at 120 °C.

Synthesis of Diketopyrrolopyrrole Containing Copolymers: A Study of Their Optical and Photovoltaic Properties

Abstract: The diketopyrrolopyrrole-based copolymers PDPP-BBT and TDPP-BBT were synthesized and used as a donor for bulk heterojunction photovoltaic devices. The photophysical properties of these polymers showed absorption in the range 500−600 nm with a maximum peak around 563 nm, while TDPP-BBT showed broadband absorption in the range 620 − 800 nm with a peak around 656 nm. The power conversion efficiencies (PCE) of the polymer solar cells based on these copolymers and [6,6]-phenyl C61 butyric acid methyl ester (PCBM) were 0.68% (as cast PDPP-BBT:PCBM), 1.51% (annealed PDPP-BBT:PCBM), 1.57% (as cast TDPP-BBT:PCBM), and 2.78% (annealed TDPP-BBT:PCBM), under illumination of AM 1.5 (100 mW/cm2). The higher PCE for TDPP-BBT-based polymer solar cells has been attributed to the low band gap of this copolymer as compared to PDPP-BBT, which increases the numbers of photogenerated excitons and corresponding photocurrent of the device. These results indicate that PDPP-BBT and TDPP-BBT act as excellent electron donors for bul...

The importance of various anchoring groups attached on porphyrins as potential dyes for DSSC applications

Abstract: In the design of new chromophores, with high efficiency, chemical stability and low cost materials for dye sensitized solar cells, porphyrin macrocycles could play a very important role. Their successful use in nature during photosynthesis must be the inspiration for new artificial antenna systems. Porphyrins offer an excellent platform for building such multi-chromophoric systems to self-assemble because of the availability of several substituent sites and their intrinsic spectroscopic properties. Specifically, their high absorption ability in the visible region can be extended, and electron donor and anchoring groups with high chemical affinity to the cell should be part of the new design. This review provides a summary of some of the most important developments and approaches that are used in order to improve the light collection efficiency of DSSCs based on porphyrin hybrid derivatives. For this reason we have attempted to describe the developments in the DSSCs of various porphyrin dyes with different anchoring groups linked through either meso or β-positions. Also, the influence of the anchoring groups in the cell performance is discussed. Studies containing chromophores other than porphyrin derivatives are not included in this work.

Investigations of materials and device structures for organic semiconductor solar cells

Abstract: In our work with the phthalocyanines and perylenes, we have formulated a hierarchy of placement of dyes in p-n heterojunction de- vices to optimize the short-circuit current density. Computer modeling of Schottky barrier cells, with parameters fit to experimental results and incorporating field-dependent carrier generation, were used to optimize the power efficiency. The model predicts an optimum carrier concentra- tion density and suggests different hierarchies for utilization of Forster radiationless energy transfer. Synthesis and purification of materials is also discussed. In terms of purity, most materials used in the literature are shown to have been quite below solar grade. A newly devised pu- rification technique is introduced. A hydration mechanism is shown to exist for chloroaluminum phthalocyanine, previously thought immune to hydration. The latter mechanism had been mistaken before for a simple phase transformation and can be induced by various different treatments with organic nonsolvents for chloroaluminum phthalocyanine. Testing of p-n and Schottky barrier cells is also discussed. The different capaci- tance versus voltage (C-V) spectroscopies are compared, and the case for the small-signal method is argued over the triangular voltage sweep. Several cautions on the interpretation of the C-V curves are noted.

π-Conjugated Polymers for Organic Electronics and Photovoltaic Cell Applications†

Abstract: The optoelectronic properties of polymeric semiconductor materials can be utilized for the fabrication of organic electronic and photonic devices. When key structural requirements are met, these materials exhibit unique properties such as solution processability, large charge transporting capabilities, and/or broad optical absorption. In this review recent developments in the area of π-conjugated polymeric semiconductors for organic thin-film (or field-effect) transistors (OTFTs or OFETs) and bulk-heterojunction photovoltaic (or solar) cell (BHJ-OPV or OSC) applications are summarized and analyzed.

Small molecule organic semiconductors on the move: promises for future solar energy technology.

Abstract: This article is written from an organic chemist's point of view and provides an up-to-date review about organic solar cells based on small molecules or oligomers as absorbers and in detail deals with devices that incorporate planar-heterojunctions (PHJ) and bulk heterojunctions (BHJ) between a donor (p-type semiconductor) and an acceptor (n-type semiconductor) material. The article pays particular attention to the design and development of molecular materials and their performance in corresponding devices. In recent years, a substantial amount of both, academic and industrial research, has been directed towards organic solar cells, in an effort to develop new materials and to improve their tunability, processability, power conversion efficiency, and stability. On the eve of commercialization of organic solar cells, this review provides an overview over efficiencies attained with small molecules/oligomers in OSCs and reflects materials and device concepts developed over the last decade. Approaches to enhancing the efficiency of organic solar cells are analyzed.

Small molecule semiconductors for high-efficiency organic photovoltaics

Abstract: Organic photovoltaic cells (OPVs) are a promising cost-effective alternative to silicon-based solar cells, and possess light-weight, low-cost, and flexibility advantages. Significant progress has been achieved in the development of novel photovoltaic materials and device structures in the last decade. Nowadays small molecular semiconductors for OPVs have attracted considerable attention, due to their advantages over their polymer counterparts, including well-defined molecular structure, definite molecular weight, and high purity without batch to batch variations. The highest power conversion efficiencies of OPVs based on small molecular donor/fullerene acceptors or polymeric donor/fullerene acceptors are up to 6.7% and 8.3%, respectively, and meanwhile nonfullerene acceptors have also exhibited some promising results. In this review we summarize the developments in small molecular donors, acceptors (fullerene derivatives and nonfullerene molecules), and donor–acceptor dyad systems for high-performance multilayer, bulk heterojunction, and single-component OPVs. We focus on correlations of molecular chemical structures with properties, such as absorption, energy levels, charge mobilities, and photovoltaic performances. This structure–property relationship analysis may guide rational structural design and evaluation of photovoltaic materials (253 references).

Rylene and related diimides for organic electronics.

Abstract: Organic electron-transporting materials are essential for the fabrication of organic p-n junctions, photovoltaic cells, n-channel field-effect transistors, and complementary logic circuits. Rylene diimides are a robust, versatile class of polycyclic aromatic electron-transport materials with excellent thermal and oxidative stability, high electron affinities, and, in many cases, high electron mobilities; they are, therefore, promising candidates for a variety of organic electronics applications. In this review, recent developments in the area of high-electron-mobility diimides based on rylenes and related aromatic cores, particularly perylene- and naphthalene-diimide-based small molecules and polymers, for application in high-performance organic field-effect transistors and photovoltaic cells are summarized and analyzed.