In this work, we study the technique of Titanium Dioxide(TiO2) work electrode of the dye sensitized solar cells. The research contained four parts. (I)Fabrication of porous TiO2 with sol-gel method. (II)Compare the efficiency between dense layer non-dense layer. (III)Study the characteristics of nanometer photocatalyzer layer with silver atom on porous layer. (IV)Replace the commercial dye with the novel Discotic Liquid Crystal(DLC) material which we synthesized. We compared different TiO2 particle size, and discovered the efficiency of 20nm particle which made Degussa reached 3.31%. After joining dense layer, the efficiency can be up to 3.75%. Finally, we sprayed a silver atom layer, the device efficiency increase to 4.13%. Because of the cost of the commercial dye, we replace the dye with DLC which were synthesized by ourselves. The efficiency is up to 0.46%. We offer a feasible direction in low cost and high-efficiency at present.

Thesis (M.S.)--Rutgers University, 2008. / "Graduate Program in Physics." Includes bibliographical references (p. 83-87).

Thesis (Ph. D.)--University of South Florida, 2003. / Includes vita. Title from PDF of title page. Document formatted into pages; contains 204 pages. Includes bibliographical references.

Solar photovoltaic industry is a hot research field, massive attempts are going on all over the world to increase its productivity in different ways. One of the challenges for solar cells is the light spectrum mismatch losses, which referred to the part of solar spectrum that cannot be utilized to electricity by the conventional cells. Two ways have been suggested to overcome solar spectrum mismatch losses, the first is multi layered cells (tandem cells) with a different light behavior for each layer, and the second is spectrum conversion which is this researches subject. Spectral modification or conversion in solar cells industry has been studied and different lab scale models have been introduced. According to nanoscale journal, such technology may be the base of the next generation solar cells, mentioning specifically the use of luminescence down conversion and up conversion techniques to control the light spectrum on the solar cell, these endeavors targets to produce solar cells that is not subjugated to Shockley-Queisser maximum efficiency limit of 31%. This research aims to draw a map of various ideas introduced to incorporate similar technologies in solar cell products, beside further suggestion to enhance its technical behavior and to push the commercialization of the technology forward. This is expected to reveal clear image about technology’s future development map for the upcoming studies, and to create a motivation for further studies towards a commercial production scale. The proposed commercialized model will result in enhancing the maximum theoretical efficiency limit to 48% if all spectral mismatch loses have been eliminated. Quantum energy level diagrams have been illustrated to describe each model’s performance under a theoretical light spectrum.

Organic solar cells (OSCs) are promising candidates for solar light harvesting due to their standout advantages both in material properties and manufacturing process. During past decades, remarkable progress has been achieved. Efficiency for single-junction cells over 9% and tandem cells over 10% has been reported. For high performance OSCs towards commercialization, sufficient light absorption and high quality buffer layers are still two challenges, which are addressed in this thesis by investigating the plasmonic effects on OSCs and interface engineering. Here, the mechanisms of plasmonic effects on OSC are explored by incorporating metallic Au nanoparticles (NPs) in individual anode buffer layer and active layer, respectively, and finally in both layers simultaneously. When Au NPs are incorporated into the buffer layer, surface plasmonic resonance (SPR) induced absorption enhancement due to incorporation of Au NPs is evidenced theoretically and experimentally to be only minor contributor to the performance improvement. The increased interfacial contact area between the buffer layer and active layer, together with the reduced resistance of the buffer layer due to the embedded Au NPs, are revealed to benefit hole collection and thus are main contributors to the performance improvement. When Au NPs are embedded in the active layer, Au NPs induced SPR indeed contributes to enhanced light absorption. However, when large amount of Au NPs are incorporated, the negative effects of NPs on the electrical properties of OSCs can counter-diminish the optical enhancement from SPR, which limits the overall performance improvement. When Au NPs are embedded into both layers, both advantages of incorporating NPs in individual layers can be utilized together to achieve more pronounced improvement in photovoltaic performance; as a result, accumulated enhancements in device performance can be achieved. The results herein are applicable to other metallic NPs such as Ag NPs, Pt NPs, etc. The study herein has clarified the degree of contribution of SPR effects on OSCs and revealed the mechanisms behind. It has also highlighted the importance of considering both optical and electrical effects when employing metallic NPs as strategies to enhance the photovoltaic performance of OSCs. Consequently, the study contributes both physical understanding and technological development of applying metallic NPs on OSCs. Regarding interface engineering, we first propose a simple method to modify the substrate work function for efficient hole collection by using an ultra-thin ultraviolet-ozone treated Au. The method can be used in other situations such as modifying the work function of multilayer graphene as transparent electrode. Then we propose a general method to synthesize solution-processed transition metal oxides (TMOs). Besides high material quality, desirable electrical properties, and good stability, our method stands out particular in that the synthesized TMOs can be dispersed in water-free solvents and the TMO films require only low temperature treatment, which is very compatible with the organic electronics. Our method can also be used to synthesize other TMOs other than the demonstrated molybdenum oxide and vanadium oxide. The proposed method herein is applicable in semiconductor industry. / published_or_final_version / Electrical and Electronic Engineering / Doctoral / Doctor of Philosophy

In this thesis, fabrication of polymer solar cells through different device designs is presented and the resulted solar cell performance is discussed. Poly(3-hexylthiophene) (P3HT) and [6,6]-phenyl-C61-butyric acid methyl ester (PCBM) are chosen as the photoactive layer materials as this material combination has been widely used and well investigated. The known properties of P3HT and PCBM make systematical studies and modeling for the effect of device designs on the performance of polymer solar cells possible although this is beyond the scope of this thesis. First, ITO electrodes were fabricated by sputtering and used as the transparent electrode for polymer solar cells. Properties of ITO film fabricated by different sputtering conditions were compared. Radio frequency (RF) sputtered ITO was found to exhibit the best transparency overall. This condition was further applied to the fabrication of ITO electrode for polymer solar cells with light trapping structures. Low temperature processed silicon oxide (SiOx) / titanium oxide (TiOx) periodic structures were fabricated by sol-gel method. Optical transmittance of the bottom electrode was altered by the presence of the reflective coating and thus the absorption in the photoactive layer was affected. By varying the number of layer pairs and thickness of each layer in the reflective coating, improvement of polymer solar cell performance was found by inserting reflective coating for optimized conditions. Finally, semi-transparent polymer solar cells with inverted structure were demonstrated using conductive polymer as the anode. The process in device preparation was vacuum-free and thus could be potentially useful in large-scale roll-to-roll fabrication. / published_or_final_version / Physics / Master / Master of Philosophy

Dye-sensitized solar cells (DSSC) have drawn much attention due to their higher versatility and lower production cost compared to inorganic photovoltaics. The top performers of DSSC have achieved power conversion efficiency over 10%, which is comparable to amorphous silicon solar cells. In this work, new photosensitizers and nanostructure for improving the photovoltaic performance of DSSC were developed and evaluated. Two series of cyclometalated ruthenium(II) complex photosensitizer were presented and their photosensitizing properties in DSSC were studied. Eight cyclometalated ruthenium(II) terpyridine complexes with three carboxylic acid groups on the terpyridine ligand were synthesized. Series A (M1 to M4) consist of C,N,N’ ligands substituted with phenyl group whereas series B (M5 to M8) consist of C,N,N’ ligands substituted with m-fluorophenyl group. All of the complexes exhibited broad aborption spectra covering the whole visible spectrum. The complexes in series B generally showed better photovoltaic performance than those in series A in the DSSCs. DSSC fabricated from M7 achieved the highest Voc, Jsc and power conversion efficiency among other DSSC, which were 0.56 V, 7.30 mAcm-2 and 2.63 % respectively. Truxene-core donor--acceptor dyes were presented and their photosensitizing properties in DSSC were studied. Eight dyes with either one donor two acceptors system (T2, B2, T2R and B2R) or two donor one acceptor system (T1, B1, T1R and B1R) were synthesized. Dyes with two acceptors have high molar extinction coefficients originated from the charge-transfer transition band, which are almost two times higher than those with only one accceptors. Both the enhanced absorption and better anchoring geometry on TiO2 contribute to the better photovoltaic performance of the two acceptors dyes in the DSSCs. Devices fabricated from B2 and volatile solvent electrolyte exhibited the best photovoltaic performance among the truxene-core dyes. The Voc, Jsc, FF and power conversion efficiency of the device were 0.59 V, 9.69 mAcm-2, 0.63 and 3.62 % respectively. Dyes based on cyanoacrylic acid anchoring groups (T1, T2, B1 and B2) were found to perform better than those based on rhodanine-3-acetic acid dyes (T1R, T2R, B1R and B2R) in both donor--acceptor configurations. ITO nanorod/TiO2 nanoparticle composite films with the three different types of ITO nanorod with different length (150 nm, 600 nm and 1.5 μm) were fabricated on FTO glass substrate. The transmittance and sheet resistance of the ITO nanorod array on the FTO glass substrate were found decreased with increasing the length of the ITO nanorod. When the ITO nanorod/TiO2 nanoparticle composite films were applied as the anode in DSSCs, the device fabricated from 600 nm ITO nanorod with TiO2 ‘double layer‘ film showed enhanced photocurrent generation. The improved photocurrent generation is suggested to be due to an improved charge collection efficiency at the ITO nanorod back electrode. / published_or_final_version / Chemistry / Doctoral / Doctor of Philosophy

Organic solar cells (OSCs) have recently attracted considerable research interest. However, there is a mismatch between their optical absorption length and charge transport scale. Attempts to optimize both the optical and electrical properties of the photoactive layer of OSCs have inevitably resulted in demands for rationally designed device architecture. Plasmonic nanostructures have recently been introduced into solar cells to achieve highly efficient light harvesting. The remaining challenge is to improve OSC performance using plasmonic nanotechnology, a challenge taken up by the research reported in this thesis. I systematically investigated two types of plasmonic effect: localized plasmonic resonances (LPRs) and surface plasmonic resonances (SPRs). Broadband plasmonic absorption is obviously highly desirable when the LPR effect is adopted in OSCs. Unfortunately, typical nanomaterials possess only a single resonant absorption peak, which inevitably limits the power conversion efficiency (PCE) enhancement to a narrow spectral range. To address this issue, I combined Ag nanomaterials of different shapes, including nanoparticles and nanoprisms. The incorporation of these mixed nanomaterials into the active layer resulted in wide band absorption improvement. My results suggest a new approach to achieving greater overall enhancement through an improvement in broadband absorption. I also explored the SPR effect induced by a metal patterned electrode with two parts. Most reports to date on back reflector realization involve complicated and costly techniques. In this research, however, I adopted a polydimethylsiloxane (PDMS)-nanoimprinted method to produce patterned back electrodes in OSCs directly, which is a very simple and efficient technique for realizing high-performance OSCs in industrial processes. Besides, a remaining challenge is that plasmonic effects are strongly sensitive to light polarization, which limits plasmonic applications in practice. To address this issue, I designed three-dimensional patterns as the back electrode of inverted OSCs, which simultaneously achieved highly efficient and polarization-independent plasmonic OSCs. In addition to investigating the two types of plasmonic effect individually, I also investigated their integrated function by introducing both LPRs and SPRs in one device structure. With the aim of achieving high-performance OSCs, I first demonstrated experimentally a dual metal nanostructure composed of Au nanoparticles (i.e. LPRs) embedded in the active layer and an Ag nanograting electrode (i.e. SPRs) as the back reflectors in inverted OSCs, which can generate a very strong electric field, in a single junction to improve the light absorption of solar cells. As a result, the PCE of the OSC reached 9.1%, making it one of the best-performing OSCs reported to date. In addition, as an important extension, I subsequently achieved tremendous near-field enhancement owing to multiple couplings, including nanoparticle-nanoparticle (LPR-LPR) couplings and nanoparticle-film (LPR-SPR) couplings, by designing a novel nanoparticle-film coupling system through the introduction of ultrathin monolayer graphene as a well-defined sub-nanogap between the Ag nanoparticles and Ag film. The graphene sub-nanogap is the thinnest nanogap (in atomic scale terms) to date, and thus constitutes a promising light-trapping strategy for improving future OSC performance. / published_or_final_version / Electrical and Electronic Engineering / Doctoral / Doctor of Philosophy

With the growing needs for energy, photovoltaic solar cells have attracted increasing research interests owing to its potentially renewable, feasible and efficient applications. Compared to its inorganic counterparts, organic solar cell (OSC) is highly desirable due to the low-cost processing, light weight, and the capability of flexible applications. While rapid progress has been made with the conversion efficiency approaching 10%, challenges towards high performance OSCs remain, including further improving device efficiency, fully realizing flexible applications, achieving more feasible large-area solution process and extending the stability of organic device. Having understood the key technical issues of designing high performance OSCs, we focus our work on (1) introducing flexible graphene transparent electrodes into OSCs as effective anode and cathode; (2) interface engineering of metal oxide carrier transport layers (CTLs) in OSCs through incorporating plasmonic metal nanomaterials ;(3)proposing novel film formation approach for solution-processed CTLs in OSCs in order to improve the film quality and thus device performance. The detailed work is listed below: 1. Design of transparent graphene electrodes for flexible OSCs Flexible graphene films are introduced into OSCs as transparent electrodes, which complement the flexibility of organic materials. We demonstrate graphene can function effectively as both the anode and cathode in OSCs: a) Graphene anode: we propose an interface modification for graphene to function as anode as an alternative to using aconventional polymer CTL. Using the proposed interfacial modification, graphene OSCs show enhanced performance. Further analysis shows that our approach provides favorable energy alignment and improved interfacial contact. b) Graphene cathode: efficient OSCs using graphene cathode are demonstrated, using a new composite CTL of aluminum-titanium oxide (Al-TiO2).We show that the role of Al is two-fold: improving the wettability as well as reducing the work function of graphene. To facilitate electron extraction, self-assembledTiO2is employed on the Al-covered graphene, which exhibits uniform morphology. 2. Incorporation of plasmonic nanomaterialsinto the metal oxide CTLinOSCs By incorporating metallic nanoparticles (NPs) into the TiO2CTLin OSCs, we demonstrate the interesting plasmonic-electrical effect which leads to optically induced charge extraction enhancement. While OSCs using TiO2CTL can only operate by ultraviolet (UV)activation, NP-incorporated TiO2enables OSCs to perform efficiently at a plasmonic wavelength far longer than the UV light. In addition, the effciency of OSCs incorporated with NPs is notably enhanced. We attribute the improvement to the charge injection of plasmonically excited electrons from NPs into TiO2. 3. Formation of uniform TiO2CTLfor large area applications using a self-assembly approach A solution-processed self-assembly method is proposed for forming large-area high-quality CTL films. Owing to the careful control of solvent evaporation, uniform film is formed, leading to enhanced OSC performance. Meanwhile, our method is capable of forming large-area films. This approach can contribute to future low-cost, large-area applications. / published_or_final_version / Electrical and Electronic Engineering / Doctoral / Doctor of Philosophy

In this work we proposed and demonstrated a novel and very cost effective method to fabricate bifacial solar cells with conventional structure. Bifacial cells collect sunlight from both faces, and hence have an obvious advantage over monofacial cells by occupying the same physical area and converting solar energy to electricity more efficiently. Despite this fact, bifacial cells are not that popular simply because of the costs associated with them. These costs are related to both manufacturing of the actual cells and integration of modules/solar panels. The cost of manufacturing is higher than regular commodity cells because the number of processing steps for fabrication is higher than their monofacial counterparts. The main reasons for that is a necessity of some kind of lithography step and/or alignment to make the grid pattern on both sides separately. Also metallization has to be done on both sides separately, one at a time. The method proposed in this work gets rid of both of those limitations by use of a lithography/alignment-less method for patterning contact holes, and a low temperature metallization scheme used for both the front and rear surfaces to grow metal simultaneously. This technique is simple and cost effective enough to be potentially incorporated in a batch process in industry, thereby reducing the cost of manufacturing. In this thesis we have presented preliminary results from the cells (bifacial and monofacial) fabricated using the above technique with proposals for further improvements. The measurement data underscores the clear advantage in using bifacial cells over monofacial cells fabricated using this method, in terms of efficiency. This also demonstrates that this proposed method is a viable way to manufacture bifacial cells with lower cost and relative ease. We also fabricated and measured monofacial solar cells in order to study the beneficial effects of including buried contacts as a possible part of device structure. The study shows significant improvement in efficiency due to incorporation of deep trenches for metal contacts in device design. / text