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Title: Solution-Processing of Chalcogenide Nanoparticles and Thin Films for Photovoltaic Applications
Author: Carreté, Àlex
Director: Cabot i Codina, Andreu
Cornet i Calveras, Albert
Keywords: Electrònica
Energia fotovoltaica
Photovoltaic power generation
Issue Date: 29-May-2015
Publisher: Universitat de Barcelona
Abstract: [cat] Avui en dia, la major part de la industria fotovoltaica està basada en el silici. Aquesta és una tecnologia provada i robusta, però, a causa de l’alt cost dels wafers de silici, el seu potencial de reducció de costos sembla limitat. Així, s’ha desenvolupat una segona generació de cel.les solars, formada per capes primes de semiconductors inorgànics, que gràcies al consum reduït de material semiconductor permet la fabricació de cel·les solars de baix cost. Les tecnologies de capa prima són actualment comercials i presenten eficiències records de fins a 20%, a escala de laboratori. No obstant això, en general els semiconductors de banda prohibida directa, CdTe i CIGS, contenen elements tòxics i poc abundants, com In, Ga o Cd. Una excel.lent alternativa a aquests materials és el CZTS, ja que està format per elements no tòxics i abundants. Aquesta tesi explica el treball fet en la preparació i caracterització de capes primes de CIGS i CZTS mitjançant tècniques de processat en solució, utilitzant tintes de nanopartícules preparades prèviament mitjançant síntesis col·loïdal. Les etapes seguides i detallades en aquesta tesi són les següents: 1. Obtenció d’una solució de nanopartícules de CIGS i CZTS mitjançant síntesi col·loïdal. 2. Preparació de capes primes de CIGS i CZTS usant tècniques de processat en solució mitjançant les nanopartícules de CIGS i CZTS. S’ha establert la composició de la tinta amb la qual obtenim capes sense defectes superficials i lliures d’esquerdes. 3. Seguidament, s’han establert els paràmetres per realitzar el correcte tractament tèrmic per tal d’obtenir un material cristal·lí. 4. Finalment un cop establertes les condicions per obtenir capes primes amb les propietats òptimes per al funcionament d’una fotovoltaica, procedirem al muntatge de la mateixa i a la mesura dels paràmetres fotovoltaics aixi com la seva eficiència mitjançant simulador solar.
[eng] Thin film solar cells based on direct band gap semiconductors have attracted much research during last decades. Thin film technologies are currently commercial and display record power conversion efficiencies up to 20% at the laboratory scale. However, typical direct band gap semiconductors, CdTe and CuIn1-xGaxS2 (CIGS), content scarce and/or toxic elements such as In, Ga or Cd. An alternative to these materials is Cu2ZnSnS4 (CZTS), formed by abundant and non toxic elements. CZTS is a quaternary p-type semiconductor which presents great absorption coefficient (> 104 cm-1), has similar crystalline structure and optical properties to CIGS, and a suitable and tunable band gap (1.00-1.5 eV) by varying the S/Se ratio. An interesting strategy to develop thin film solar cells is the solution processing. Solution based approaches are especially interesting for their potential low production costs and their easy scalability. Among different solution processing techniques, the spraying of nanocrystals or metal salts is an especially interesting approach. The easy scalability of spraying techniques to prepare large-area panels in a non vacuum atmosphere, which is translated in a significant reduction of the production costs, renders the spraying very attractive for industrial implantation. A pulsed spray deposition system, which was custom made and operates in open air, is here used to produce CIGS and CZTS films from colloidal CIGS and CZTS NPs. This work is divided in 5 chapters. The 1st chapter is an introduction to the photovoltaic (PV) technology and in particular to thin film PV technology, with special focus to chalcopyrite CIGS and kesterite CZTS. In the 2nd chapter I review the work done towards solving one of the major challenges associated to NP-based PV technologies: the complexity to transform NPs into highly crystalline thin films by sintering processes. The 3rd chapter describes the experimental procedures used to prepare all the required materials and thin films and to fabricate solar cells. This chapter also describes the techniques used to characterize the morphological, compositional, structural and optoelectronical properties of the materials and films. Chapter 4 and 5 describe the work done regarding CIGS and CZTS technologies, respectively. Both chapters describe: NP colloidal synthesis, ligand exchange strategies to remove organic carbon surrounding the NP, subsequent thin film deposition techniques used, thermal treatments performed and final hetero-junction formation and device completion. Chapter 5 also describes a scale up method to produce large quantities of NPs using a continuous flow reactor. In summary, the goal of this thesis is to establish a non vacuum technology to produce CIGS and CZTS PV devices prepared by solution process of the absorber. Additionally, drawbacks involved in the solution processing of NP-based films, such as elimination of organic carbon present in NP and film crystallization are addressed.
Appears in Collections:Tesis Doctorals - Departament - Electrònica

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