Organic solar cells (OSCs) are of interest because the technology offers a significant opportunity to reduce the overall costs of solar energy. OSCs can be very inexpensive to produce given that they rely on non-commodity materials and can use existing manufacturing techniques that are not labour- and capital-intensive. In this research, a financial model, named TEEOS (Technological and Economic Evaluator for Organic Solar), is developed and is used to determine financial indicators, such as simple payback period. These indicators are used to determine technical objectives for the OSCs. Two sample cells are evaluated in Toronto, Canada using historical data. The results show that the cell with a higher efficiency and wider absorptive wavelength range produces a payback period of approximately nine years, while the other cell has a payback period well over 45 years. Stochastic modeling techniques are also used to better replicate electricity price and weather fluctuations.

Submitted by Juan Carlos Roldão null (36780115860) on 2016-04-28T18:17:40Z No. of bitstreams: 1 Dissertação-Versão-Final-Juan_Carlos_Roldao.pdf: 3885340 bytes, checksum: 0d245c89d075ddeea3f1fc7154e9c5a9 (MD5) / Approved for entry into archive by Felipe Augusto Arakaki (arakaki@reitoria.unesp.br) on 2016-05-02T13:34:47Z (GMT) No. of bitstreams: 1 roldao_jc_me_bauru.pdf: 3885340 bytes, checksum: 0d245c89d075ddeea3f1fc7154e9c5a9 (MD5) / Made available in DSpace on 2016-05-02T13:34:47Z (GMT). No. of bitstreams: 1 roldao_jc_me_bauru.pdf: 3885340 bytes, checksum: 0d245c89d075ddeea3f1fc7154e9c5a9 (MD5) Previous issue date: 2016-03-03 / Coordenação de Aperfeiçoamento de Pessoal de Nível Superior (CAPES) / Atualmente existe uma intensa busca por novos materiais com propriedades ajustadas para utilização em células solares orgânicas de modo a obter um aumento em sua eficiência de conversão para que possam substituir os dispositivos de silício. O politieno[3,4-b]-tiofeno-co-benzoditiofeno (PTB7) é um polímero recentemente proposto na literatura e com propriedades muito interessantes em células solares orgânicas, o que o coloca como uma possível alternativa ao amplamente utilizado poli(3-hexiltiofeno) (P3HT). Tem sido relatadas modificações em diferentes posições da unidade monomérica deste copolímero, tanto na estrutura benzoditiofeno (BDT), quanto na estrutura tienotiofeno (TT), que o compõe. Estas modificações levaram a novos polímeros com propriedades diferentes e por vezes mais interessantes que aquelas do PTB7 sem substituições. O trabalho que será apresentado visou estudar as propriedades estruturais, eletrônicas e ópticas do PTB7 e possíveis alterações ocorridas devido às modificações químicas realizadas na estrutura do BDT de suas unidades monoméricas. Tal estudo utilizou ferramentas de otimização de estruturas como Mecânica Molecular, Dinâmica Molecular e o método semi-empírico Parametric Method 6 (PM6), assim como de cálculo de estrutura eletrônica de materiais, como a Teoria do Funcional da densidade (DFT) e de cálculos de propriedades ópticas como a Teoria do Funcional da Densidade Dependente do Tempo (TD-DFT). Concluímos que o PTB7 no estado sólido pode ser considerado planar. Com o nosso modelo para o PTB7, obtivemos uma diferença de energia ∆EHL entre o Último Orbital Molecular Ocupado HOMO (do inglês Highest Occupied Molecular Orbital) e o Primeiro Orbital Molecular Desocupado LUMO (do inglês Lowest Unoccupied Molecular Orbital) de aproximadamente 1,84 eV, sendo que este valor está em boa concordância com o valor experimental. Em relação às substituições químicas, estudamos teoricamente 8 derivados do PTB7 e os resultados mostraram que é possível obter compostos com uma diminuição significativa do ∆EHL e também que é possível obter compostos com valores de energia do HOMO e do LUMO mais interessantes que os do PTB7 quando na camada ativa for empregado como material doador o fenil-C61-butírico ácido metil ester (PCBM). / Currently there is an intensive search for new materials with tuned properties for use in organic solar cells to obtain an increase in its conversion efficiency and replace silicon devices. The polythieno[3,4-b]-thiophene-co-benzodithiophene (PTB7) is a polymer recently proposed in the literature and with very interesting properties in organic solar cells, which places it as a possible alternative to the widely used poli(3-hexilthiophene) (P3HT). It has been reported changes in different positions of the monomeric unit of this copolymer, both in benzodithiophene (BDT) structure, as in the thienothiophene (TT) structure that compose it. These modifications led to new polymers with different properties and sometimes more interesting than those of PTB7 without substitutions. The work to be presented aimed to study the structural, electronic and optical properties of PTB7 and possible changes due to chemical changes made in the BDT structure of its monomeric units. This study employed optimization tools like Molecular Mechanics, Molecular Dynamics and Parametric Method 6 (PM6), as well as calculations of the electronic structures with the Density Functional Theory (DFT) method, and optical properties such as the Time Dependent Density Functional Theory (TD-DFT) calculations. We conclude that the PTB7 chains in the solid state can be considered planar. With our model for PTB7, we obtained a difference ΔEHL between the Highest Occupied Molecular Orbital (HOMO) and the Lowest Unoccupied Molecular Orbital (LUMO) of approximately 1.84 eV, and this value is in good agreement with the experimental value. Regarding chemical substitutions, we studied theoretically 8 derivatives of PTB7 and the results showed that it is possible to obtain compounds with a significant decrease in ΔEHL and that it is possible to obtain compounds with HOMO and LUMO energy values more adjusted to the widely employed acceptor material phenylC61-butyric acid methyl ester (PCBM).

abstract: In this work a newly fabricated organic solar cell based on a composite of fullerene derivative [6,6]-phenyl-C61 butyric acid methyl ester (PCBM) and regioregular poly (3-hexylthiophene) (P3HT) with an added interfacial layer of AgOx in between the PEDOT:PSS layer and the ITO layer is investigated. Previous equivalent circuit models are discussed and an equivalent circuit model is proposed for the fabricated device. Incorporation of the AgOx interfacial layer shows an increase in fill factor (by 33%) and power conversion efficiency (by 28%). Moreover proper correlation has been achieved between the experimental and simulated I-V plots. The simulation shows that device characteristics can be explained with accuracy by the proposed model. / Dissertation/Thesis / Masters Thesis Electrical Engineering 2015

As células solares orgânicas, também conhecidas como (OPVs), fazem parte da terceira geração dos dispositivos fotovoltaicos. Entre outras tecnologias emergentes, a dos OPVs tem a vantagem de ser de fácil processamento e de baixo custo. Ou seja, uma tecnologia comercialmente promissora na área de conversão de energia solar em energia elétrica. No entanto, grandes desafios precisam ser superados para colocar estas células no mercado dos fotovoltaicos. Dentre esses desafios, pode estar incluído, inevitavelmente, a compreensão dos processos físicos envolvidos na fotogeração em OPVs, dentre os quais pode-se destacar o da recombinação de cargas fotogeradas. A recombinação é o principal responsável pela perda de eficiência em OPVs, uma vez que ela elimina uma fração relativamente grande de portadores de carga, diminuindo consideravelmente a potência de saída da célula. Para estudar este efeito indesejado em células orgânicas, desenvolvemos um modelo analítico para fotocorrente em OPVs do tipo bulk heterojunction (BHJ), assumindo uma recombinação bimolecular de cinética de segunda ordem. O modelo é representado por uma expressão analítica obtida a partir das equações fundamentais da eletrodinâmica clássica, onde despreza-se a contribuição da corrente de difusão e as mobilidades dos elétrons e dos buracos são consideradas iguais. Essa expressão foi de grande valia na análise dos resultados experimentais, sobretudo os de corrente-tensão (J-V) sob iluminação, e além disso, ela permitiu extrair parâmetros intrínsecos do transporte de carga, como mobilidade e coeficiente de recombinação. Neste sentido, foram fabricados dispositivos cuja estrutura foi ITO/PEDOT:PSS/P3HT:PCBM/Ca/Al, e com eles foram realizados inúmeros experimentos. As técnicas usadas na parte experimental foram: medidas J-V, no escuro e sob iluminação, medidas de transiente de fotovoltagem (TPV), de transiente de fotocorrente (TPC), e de Foto-CELIV (Charge Extraction Linear Increasing Voltage). Usamos como parâmetros experimentais a temperatura e intensidade de iluminação. Das medidas J-V sob iluminação, foram extraídos os parâmetros essenciais da célula: corrente de curto (Jsc), potencial de circuito aberto (Voc), fator de preenchimento (FF) e a eficiência (PCE). A partir das abordagens experimental e teórica, exploramos a influência da recombinação bimolecular no comportamento fotovoltaico dos dispositivos. O desenvolvimento do modelo teve contribuição de trabalhos que se basearam em modelagem numérica a partir de condições físicas semelhantes às usadas em nosso tratamento e que foram levadas em consideração no processo de análise dos resultados experimentais. / Organic solar cells, also known as (OPVs), are part of the third generation of photovoltaic devices. Among other emerging technologies, OPVs have the advantage of being easy to process and exhibits low cost of production. That is, it is a promising commercial technology in the area of converting solar energy into electricity. However, major challenges need to be overcome to put these cells in the photovoltaic market. Among them, it can be included, inevitably, the comprehension of the physical processes involved in photogeneration in OPVs, of which, the recombination of photogenerated carriers is included. Recombination is primarily factor responsible for the loss of efficiency in OPVs, since recombination eliminates a large fraction of the carriers, considerably reducing the output power of the cell. To study this undesirable effect in organic cells, we developed an analytical model for the photocurrent in bulk heterojunction cells (BHJ), which assumes the bimolecular recombination of second order kinetics. The model is represented by an analytical expression obtained by the equations of the classical electrodynamics, where we neglected the contribution of the diffusion current and assumed that electrons and holes have equal mobilities. The expression was of great value for the analysis of the experimental results, especially the current-voltage (J-V) measurements under illumination, and it allowed to extract intrinsic parameters of charge transport effects, such as mobility and recombination coefficient. For this, it were fabricated devices whose structure was ITO/PEDOT:PSS/P3HT:PCBM/Ca-Al, and with them were performed numerous experiments. The techniques used in the experimental part were: J-V measurements, in the dark and under illumination, transient photovoltage (TPV), transient photocurrent (TPC), and of Charge Extraction Linear Increasing Voltage (Photo-CELIV). We used as experimental parameters the temperature and the intensity of. From J-V measurements under illumination we extracted the essential cell parameters: short current (Jsc), open circuit potential (Voc), fill factor (FF) and efficiency (PCE). From the experimental and theoretical approaches, we explored the influence of bimolecular recombination on the photovoltaic behavior of the devices. The development of the model had contributions of works based on numerical modelings from physical conditions similar to those used in our treatment and that were taken into account in the process of analysis of the experimental results.

Orientador: Ana Flavia Nogueira / Dissertação (mestrado) - Universidade Estadual de Campinas, Instituto de Quimica / Made available in DSpace on 2018-08-10T16:04:48Z (GMT). No. of bitstreams: 1 Lomba_BrunoStelutti_M.pdf: 2789085 bytes, checksum: c5cf56c110af4564ce46cde2fd239d4f (MD5) Previous issue date: 2007 / Resumo: Nanotubos de carbono de paredes simples (SWNT) têm atraído grande interesse devido a sua aplicação em diversas áreas de pesquisa, incluindo novos materiais e dispositivos optoeletrônicos. Entretanto uma boa dispersão destes materiais é um fator necessário na obtenção de filmes homogêneos, com menor grau de agregação para se obter dispositivos com maior desempenho. Neste trabalho, foi realizada uma modificação química das extremidades e defeitos dos SWNT com grupos tiofenos com a finalidade de melhorar a interação do nanotubo de carbono com a matriz polimérica de poli(3-octiltiofeno) (POT). De fato, células solares com melhor desempenho foram obtidas. O SWNT modificado e seu compósito com POT foram caracterizados por espectroscopia Raman, espectroscopia no infravermelho, espectroscopia UV-VIS e voltametria cíclica. A melhor célula solar de heterojunção dispersa foi obtida usando 5 % m m de SWNT modificado (SWNT-TIOF), e apresentou potencial de circuito aberto (Voc), fotocorrente (Isc) e eficiência (h) de 0,75 V, 9,5 mA cm e 0,184 %, respectivamente. O uso de um derivado de indenofluoreno (DPIF) como camada transportadora de buraco no lugar do polietilenodioxitiofeno dopado com sulfato de poliestireno (PEDOT:PPS) também foi investigado. Os resultados iniciais indicam que o uso dessa camada pode ser uma tentativa interessante para melhorar o Voc de células solares orgânicas / Abstract: Single-wall carbon nanotubes (SWNT) have attracted great interst for applications in a variety of research areas, including electronics and functional materials. However, a good dispersion of these materials is a demanding factor in order to obtain more homogeneous and less bundled films for constructing devices. In this report we describe how a covalent modification with thiophene groups at the edges and defects of SWNT can improve interaction with a polymer matrix, resulting in solar cells with improved performance. The modified SWNT and its composite with poly(3-octylthiophene) were characterized by Raman, Infrared and UV-VIS spectroscopies and cyclic voltammetry. The best bulk heterojunction solar cell was obtained using 5 wt % of the modified carbon nanotube (SWNT-THIOP) and shows open circuit voltage (Voc), photocurrent (Isc) and efficiency (h) of 0.75 V, 9.5 mA cm e 0,184 %, respectively. The use of an idenofluorene derivative as a hole transport layer in replacement of the PEDOT:PPS was also investigated. The primary results indicate that the use of this layer can be an interesting approach to improve the open-circuit voltage in polymer/nanotube solar cells / Mestrado / Quimica Inorganica / Mestre em Química

Abstract Printed electronics offer unique possibilities for the development of devices and manufacturing methods. A prime example of printed electronics where the production volume can be significantly increased are solution-processed organic solar cells. Roll-to-roll (R2R) technology has made it possible to print solar cells almost as fast as newspaper. Unfortunately, the performance of printed devices depends strongly on film morphology, which is affected by the behaviour of the used ink on the confining surface - wetting. Key parameters that influence the wetting behaviour include surface energy, ink formulation, surface roughness, solvent properties, processing temperature and pre/post-treatments (heat, acid or plasma) and chemical heterogeneity. Importantly, a precise control of wetting and, consequently, film morphology is emphasized by many authors as an important factor for the commercialization of printed solar cells. This research focuses on measuring and analysing the influence of substrate processing temperature as well as plasma and UV pre-treatments on the wettability of various inks and substrates used in Organic Solar Cell (OSC) fabrication. It also explores the application of interesting novel materials, such as nanocellulose, in solar cell manufacture. The main tool applied here is the contact angle measurement method, since it is commonly used to obtain quantitative data describing the behaviour of ink droplets on substrate surfaces. Chief among the achieved results is the finding that the three factors mentioned above significantly influence ink-substrate interactions. Therefore, manipulation of plasma and UV treatments as well as substrate processing temperature, allow us to control wetting properties and, in consequence, the printing process. Another important result shows that the degree of control is strongly dependent on ink formulation and material composition and must, therefore, be taken into account in process development. These findings will contribute to a faster development of printed solar cells and their manufacturing conditions and requirements. / Tiivistelmä Painettava elektroniikka tarjoaa uusia mahdollisuuksia elektronisten laitteiden ja niiden valmistusmenetelmien kehittämiseen. Liuoskäsitellyt orgaaniset aurinkokennot ovat hyvä esimerkki painetun elektroniikan tuotteesta, jonka tuotantomäärää on voitu kasvattaa merkittävästi. Rullalta rullalle (engl. Roll-to-roll, R2R) -menetelmän avulla aurinkokennoja voidaan painaa lähes samalla nopeudella kuin sanomalehteä. Painettujen laitteiden suorituskyky riippuu suuresti tuotetun kalvon morfologiasta, johon vaikuttavat tuotantoprosessissa käytettyjen materiaalien kostumisominaisuudet. Tärkeimmät kostumiskäyttäytymiseen vaikuttavat parametrit ovat pintaenergia, pinnan karheus, musteen koostumus, liuotinominaisuudet, käsittelylämpötila, esi- ja jälkikäsittely (lämpö, happo tai plasma) sekä kemiallinen heterogeenisyys. Kostumisen, ja sitä kautta kalvon morfologian, tarkka säätely on tärkeää painettujen aurinkokennojen kaupallisen hyödyntämisen kannalta. Tässä väitöskirjatyössä mitataan ja analysoidaan käsittelylämpötilan sekä plasma- ja UV-esikäsittelyiden vaikutuksia orgaanisten aurinkokennojen valmistuksessa käytettyjen musteiden ja alustojen kostumisominaisuuksiin sekä tarkastellaan aurinkokennoliuoksissa käytettäviä uusia, mielenkiintoisia materiaaleja, kuten nanoselluloosaa. Työssä eniten hyödynnetty menetelmä on kontaktikulman mittaus, joka on yleisesti käytetty tapa hankkia kvantitatiivista tietoa mustepisaroiden käyttäytymisestä erilaisilla pinnoilla. Keskeisin saavutettu tutkimustulos on se, että kaikilla yllämainituilla kolmella käsittelyllä on huomattava merkitys musteen ja alustan vuorovaikutuksiin. Näin ollen plasma- ja UV-käsittelyillä sekä alustan käsittelylämpötilan säätelyllä voidaan hallita kostumisominaisuuksia ja sitä kautta koko painatusprosessia. Toinen tärkeä löydös on, että musteen koostumus ja alustan materiaali vaikuttavat siihen, kuinka voimakkaasti kostumista voidaan hallita. Näin ollen ne täytyy ottaa huomioon painatusprosessin suunnittelussa. Työssä saavutettuja tuloksia voidaan käyttää painettujen aurinkokennojen sekä niiden tuotantomenetelmien kehittämiseen.

To mitigate the risk for devastating climate changes, there is an urgent need to change the energy production from the current fossil based to renewable sources. Solar cells will contribute to an increasing share of the future energy systems. Today silicon solar cells dominate the market but printed organic solar cells are promising alternatives in terms of cost, flexibility, possibilities for building integrations and energy payback times. Printing enables roll-to-roll processing that is quick and renders huge volumes. Thus, also characterization and quality control must be fast. Recent tests have been performed showing that a LED array with amplitude modulated LEDs can be used to provide photocurrent images of modules with series connected sub cells in-line during manufacturing. The purpose of this thesis work is to further evaluate and develop this LED array characterization technique focusing on contact methods and signal interpretation. Two modes were examined; a contact mode and a capacitive contact-less mode. Both modes gave comparable results and indicated strong variations in performance of sub cells in the measured modules. Other methods to address individual cells also showed similar behavior. However, by manually adding extra contact points, current-voltage curves could be measured on the individual sub cells in the modules. Extraction of photocurrents were similar, but the parallel resistances varied strongly between the cells in the module. Increasing the frequency of the LEDs resulted in less variations. Calculations indicated that this frequency dependence could be used to separate the photocurrent generation and parallel resistance in the sub cells.

The importance of renewable energy sources is becoming clearer and clearer as unsustainable energy sources are running out and global warming is getting worse. Energy derived from sunlight is already commonly used, but more energy can be produced from sunlight when solar cells become cheaper. Organic solar cells use organic compounds as semiconductors which can be prepared from solutions, resulting in lower production costs. However, these semiconductors;Poly(3-hexylthiophene) and [6,6]-Phenyl-C61-butric acid methyl ester, are commonly dissolved inhalogenated and aromatic solvents. These solvents have toxic properties, which is why alternative solvents should be identified. Potential solvents were predicted by using the Hansen solubilityparameters and thin films were prepared by spin-coating the solutions. The thin films were evaluated with absorption spectroscopy, the fluorescence spectroscopy and atomic force microscopy. Since the alternative solvents had lower solubilites than the commonly used solvents, i.e., chlorobenzene, ortho-dichlorobenzene and chloroform, the absorption of the films with new solvents were lower as well. Using tetrahydrofuran resulted in the highest absorption of the used solvents, while xylene hada better film morphology. Increasing the absorption was attempted by spin-coating multiple thin films on top each other or by using a lower rotational speed. Spin-coating multiple films had nouniform effect on the absorption, while lowering the rotational speed increased the absorption, but not enough to equal the original absorption. Contrasting the results of the absorption spectra, the morphology improved when multiple layers were used while the film with the lower rotational speed’s morphology got worse. In conclusion, tetrahydrofuran and xylene are the best alternative solvents and using multiple layers as well as decreasing the rotational speed show improvements oneither the morphology or the absorption.

Le développement de la technologie des cellules photovoltaïques organiques nécessite des compétences diverses liées à l’ingénierie moléculaire, à l’ingénierie des interfaces, au contrôle et à la caractérisation de la morphologie des films, à l’optimisation de la structure du dispositif et à la compréhension de la photo-physique des matériaux utilisés. Dans ce contexte, le travail présenté dans cette thèse contribue à la compréhension des propriétés photo-physiques des matériaux organiques π-conjugués et propose des outils de caractérisations optiques pour le suivi de la morphologie de ces matériaux. Dans un premier temps, une méthodologie rigoureuse de détermination des indices optiques des films organiques par ellipsométrie a été proposée. Les modèles utilisés en ellipsométrie ont ainsi été choisis en tenant compte des propriétés physiques des matériaux organiques π-conjugués ce qui a permis de remonter à la structure électronique de dérivés de fullèrenes (PC60BM et PC70BM). Dans un second temps, nous avons associé des données ellipsométriques à des mesures complémentaires d’absorbance et de photoluminescence dans le cas de deux copolymères (PTB7 et PTB7-Th) en films et en solutions afin d’isoler les interactions inter et intra-chaînes. Nous avons démontré que la photo-physique de ces copolymères diffère de celle du P3HT. Nous avons montré que même en solution dans le chlorobenzène, le PTB7 et le PTB7-Th s'agrègent fortement. Ces agrégats, de type H, se cassent plus facilement dans les solutions de chlorobenzène à base de PTB7-Th que dans celles à base de PTB7. / The development of organic photovoltaic cell technology requires various skills related to the molecular engineering, interface engineering, controlling and characterizing the morphology of the films, device structure optimization and understanding of photophysics of the materials. In this context, the work presented in this thesis contributes to the understanding of the photophysical properties of π-conjugated organic materials and propose optical characterizations tools for probing the morphology of these materials. First, a rigorous methodology for determining refractive indices of organic films by ellipsometry has been proposed. The models used in ellipsometry have been chosen by taking into account the physical properties of π-conjugated organic materials which allow the determination of the electronic structure of fullerene derivatives (PC60BM and PC70BM). Secondly, we associated ellipsometric data to complementary measurements of absorbance and photoluminescence in the case of two copolymers (PTB7 and PTB7-Th) in films and solutions in order to isolate inter and intra-chain interactions. We have demonstrated that the photophysics of these copolymers differs from the P3HT. We have shown that even in solution in chlorobenzene, the PTB7 PTB7-Th aggregate strongly. These aggregates, H-type, break more easily in the chlorobenzene solutions based of PTB7-Th as in those based on PTB7.

Ce travail de thèse a été consacré à l’étude de la stabilité dans différents milieux des matériaux constitutifs de la couche active des cellules solaires organiques. Les deux objectifs principaux étaient premièrement d’approfondir la compréhension sur certains mécanismes complexes intervenant dans la couche active, et deuxièmement d’étudier les processus de dégradation intervenant spécifiquement aux interfaces de la couche active au sein de la cellule. La première partie de ce mémoire est consacrée à l’étude de la dégradation photochimique et thermique de la couche active des cellules solaires en faisant varier le matériau polymère qui la constitue. La deuxième partie est dédiée au rôle d’un troisième composant de la couche active que peut être la présence d’additifs résiduels provenant de la mise en forme, ou d’un additif stabilisant ajouté à dessein. La troisième partie est consacrée au processus de délamination susceptible d’intervenir à l’interface couche active / couche transporteuse de trous. Enfin, une dernière partie concerne l’étude de l’alignement des niveaux énergétiques entre la molécule de C60 et divers substrats transporteurs d’électrons. L’influence de la lumière et de la température sur les propriétés d’interface couche active / couche transporteuse d’électrons est également reportée. / This word was devoted to the stability in various conditions of materials used in the active layer of organic solar cells. The main goals of this work were first to provide deeper understanding about complex mechanisms occurring in the active layer and second to investigate interfacial degradation pathways involving the active layer. A first part was dedicated to the photo and thermal stability of the polymer blend materials which constitute the active layer of the solar cells. A second section focused on the role of the third component of the active layer which can be undesired residual additives coming from the processing or the desired insertion of a stabilizer additive. A third part concerned the delamination issue which takes place at the active layer / hole transporting layer interface. Finally, a last section was devoted to the energy level alignment between the C60 molecules and various electron transporting substrates. The photo and thermal stability of the active layer / electron transporting layer interface was also studied in this section.