In this work, we present the ionic liquid (IL) synthesis of two novel and [Et3S][AuI4][I-5] (2), and their application as active layers in monolithic solar cells. The compounds are composed of tetraiodoaurate anions and polyiodide entities, infinite polyiodide chains in 1 and pentaiodides in 2, which display short intermolecular contacts resulting in relatively small electronic bandgaps. This work represents the first demonstration of film deposition of gold iodide/polyiodide compounds onto porous monolithic substrates with subsequent solar cell characterization. The devices show promising photovoltaic performance and could unlock new materials design possibilities, ultimately moving away from lead-based photovoltaic materials. These findings further highlight the use of simple polyiodide entities to increase the structural and electronic dimensionality of gold perovskite-type anions.

As of today, the energy consumption in the world is high and is essential in the development and growth of the modern-day society. The world energy consumption is projected to increase significantly over the next decades. The energy consumed today is predominantly based on fossil fuels, which is of serious concerns with regards to the environmental impact. Fossil fuels release large amounts of greenhouse gases, such carbon dioxide, upon burning, which in turn contributes to global warming. Moreover, fossil fuel resources are definite and are projected to run out in the near future. Therefore, there is a strong need to consume energy from cleaner, and renewable, sources. Harvesting energy from the sun is one possibility. The sun provides an enormous amount of energy and is a renewable resource. Solar cells convert sunlight to electricity in an emission free manner, which renders them one of the most promising technologies for the future. Silicon solar cells are the most common solar cell technology commercially, with relatively high efficiencies. However, solar cells based on silicon are expensive. Perovskite solar cells (PSCs) have in the last decade emerged as a new and competitive third generation photovoltaic technology with power conversion efficiencies exceeding 25%. Specifically, methylammonium lead triiodide (MAPbI3) represents the archetype of 3D perovskite material that has demonstrated high efficiencies as light-absorbing layers in solar cell devices. Despite the promising properties and the high conversion efficiencies of this class of perovskite materials, there are some important challenges that needs to be addressed prior to large-scale commercialization. The intrinsic instability of the perovskite material towards air, moisture and heat is a serious concern, leading to degradation of the active layer in the solar cell devices in a matter of days. The strict intrinsic size requirements to allow the formation of 3D perovskites limit the number of cations to only a few, which significantly restricts the chemical space for alternative 3D perovskites to be explored. In addition, concerns regarding the toxicity of the standard lead-based perovskites may, because of national legislation, hamper future commercialization. Consequently, there is a need to explore and identify alternative photovoltaic materials with suitable properties. Low-dimensional perovskites offer a vast structural and chemical space to be explored, as well as paving the way for incorporation of functional cations. Low-dimensional perovskite materials typically display relatively large bandgaps and poor charge-transport properties. Therefore, it is necessary to both develop a method to rapidly identify interesting low-dimensional candidate materials, as well as addressing the charge-transport problem. The work presented in this thesis seeks to address these issues.

The aim in this work was to synthesize and characterize novel low-dimensional, perovskite-type materials using two strategies. The first has concerned the utilization of the properties of polyiodides to synthesize new low-dimensional, perovskite-type materials incorporating polyiodide entities linking the low-dimensional framework building blocks. In the second strategy, cationic dyes were used to generate new low-dimensional perovskite compounds internally sensitized with a dye, where the dye acts as cation with respect to the inorganic host structure. In addition, the application of automated robotized screening was explored with the aim to quickly synthesize and identify novel, potentially interesting photovoltaic materials.

In Chapter 1, an introduction to the solar cell field, and especially to the PSCs is presented. In Chapter 2, an overview of the methods used in this work is presented.  

 In Chapter 3, the work using automated robotized screening for the synthesis of new low-dimensional dye-sensitized perovskite-type materials is presented and discussed. The characterization, properties and application of the materials in solar cells are also discussed. 

 In Chapter 4, the work incorporating polyiodides into low-dimensional perovskite-type materials is presented and discussed. Properties of the compounds and their application in solar cells are presented and discussed as well. 

Världens energikonsumtion är idag hög och avgörande för det moderna samhällets utveckling och tillväxt. Energikonsumtionen i världen beräknas öka signifikant under de kommande decennierna. Den energi som konsumeras idag baseras till största del på fossila bränslen, vilket är ett betydande problem ur klimatsynpunkt. När fossila bränslen förbränns så frigörs stora mängder växthusgaser, exempelvis koldioxid, vilket i sin tur bidrar till den globala uppvärmningen. Dessutom är de fossila bränsleresurserna begränsade och beräknas ta slut inom en snar framtid. Därför är det av yttersta vikt att energikonsumtionen framöver kommer från förnyelsebara källor och är koldioxidneutrala. En möjlighet är att utnyttja solens energi. Solen förser oss med enorma mängder energi och är dessutom en förnyelsebar energikälla. Solceller omvandlar solens ljus till elektrisk energi på ett utsläppsneutralt sätt, vilket gör dem till en av de mest lovande teknologierna för framtiden. Kiselsolceller hör till en av de mest etablerade kommersiella solcellsteknologierna och uppvisar relativt höga verkningsgrader. Däremot är kiselsolceller mycket dyra. Perovskitsolceller har det senaste decenniet dykt upp som en ny och konkurrenskraftig tredjegenerationens solcellsteknologi och uppvisar verkningsgrader på över 25%. Mer specifikt så är det metylammoniumblyjodid (MAPbI3), som utgör arketypen av 3D perovskitmaterial, som påvisat hög omvandlingseffekt när det använts som det ljusabsorberande lagret i solceller. Trots de lovande egenskaperna och de höga omvandlingseffekterna av denna typ av perovskitmaterial så återfinns det några viktiga aspekter som behöver adresseras innan de kan appliceras i större kommersiell skala. Den inneboende instabiliteten av perovskitmaterialet gentemot luft, fukt och värme utgör ett allvarligt problem, vilket leder till snabb degradering av det aktiva perovskitmaterialet i solcellerna inom loppet av några dagar. De strikta storlekskraven för att tillåta bildandet av 3D perovskiter begränsar antalet möjliga katjoner till endast ett fåtal, vilket avsevärt begränsar möjligheterna till att utforska den kemiska sammansättningsrymden för alternativa 3D perovskiter. Dessutom kan farhågor beträffande toxiciteten hos standard blybaserade perovskiter på grund av nationell lagstiftning hämma framtida kommersialisering. Det finns därför ett behov av att utforska och identifiera alternativa solcellsmaterial med lämpliga egenskaper. Lågdimensionella perovskiter erbjuder en stor strukturell- och kemisk sammansättningsrymd att utforska, och banar dessutom väg för inkorporering av funktionella katjoner. Lågdimensionella perovskiter uppvisar vanligtvis relativt stora bandgap och även dåliga egenskaper för laddningstransport. Därför är det nödvändigt att både utveckla metoder för att snabbt identifiera nya intressanta lågdimensionella kandidatmaterial, och att samtidigt adressera problemet med laddningstransport. Arbetet som presenteras i denna avhandling har som mål att adressera de problemen som är beskrivna.

Målet i detta arbete var att syntetisera ock karaktärisera nya lågdimensionella perovskit-liknande material genom att använda två olika strategier. I den första strategin utnyttjas egenskaperna hos polyjodider för att syntetisera nya lågdimensionella perovskit-liknande material som inkorporerar polyjodider som länkar samman de lågdimensionella perovskitbyggstenarna. I den andra strategin så användes katjoniska färgämnen för att syntetisera nya lågdimensionella perovskitföreningar som är internt sensitiserade med ett färgämne, där färgämnet utgör katjonen i perovskitstrukturen. Dessutom undersöktes möjligheten att tillämpa automatiserad robotiserad screening i syfte att snabbt syntetisera och identifiera nya och potentiellt intressanta solcellsmaterial.                       

I kapitel 1 introduceras solcellsområdet, med ett särskilt fokus på perovskitsolcellerna. I kapitel 2 presenteras de metoder som använts i detta arbete. 

I kapitel 3 presenteras och diskuteras arbetet med automatisk robotiserad screening för syntes av nya lågdimensionella färgämnessensisiterade perovskit-liknande material. Karaktärisering av materialen, deras egenskaper och tillämpning av dessa i solceller diskuteras också.

I kapitel 4 presenteras och diskuteras arbetet med att inkorporera polyjodider i lågdimensionella perovskit-liknande material. Föreningarnas egenskaper och deras tillämpning i solceller presenteras och diskuteras också.

Low-dimensional hybrid perovskite materials offer significantly improved stability as well as an extensive compositional space to explore. However, they suffer from poor photovoltaic performance as compared to the 3D perovskite materials because of poor charge-transport properties. Herein, we present the concept of internal dye-sensitized hybrid perovskite compounds involving five novel low-dimensional perovskite-type materials 1-5 incorporating triarylmethane, phenazinium and near-infrared (NIR) cyanine cationic dyes, respectively. The synthesis characterization and theoretical analysis of these compounds are presented. Theoretical calculations provide interesting insights into the effects of these dyes on the band structure of the low-dimensional anionic metal-halides and especially highlight compound 1 as a promising photovoltaic candidate. Solar cell investigation of devices based on 1 were conducted. The results show an average power conversion efficiency (PCE) of about 0.1%, which is among the highest reported for a 1D material despite the use of undoped Spiro-OMeTAD as the hole-transport material (HTM). Incident photon-to-electron efficiency (IPCE) spectra confirm the contribution of the dye to the overall photocurrent of the solar cell. Moreover, examination of solar cell devices based on the bismuth-based compound 5 resulted in PCEs in the range of 0.1%. This illustrates the potential of this concept to be exploited for lead-free photovoltaics. Finally automated robotized screening of low-dimensional hybrid perovskite materials through the screening robot PROTEUS has emerged as a powerful tool in the search for novel perovskite-like materials. Our work highlights that the use of cationic dyes could induce interesting sensitizing properties to low-dimensional metal-halide chains and may therefore provide inspiration and new design strategies for the synthesis of new lead-free photovoltaic materials

Two new organic inorganic hybrid perovskite compounds, (Me3S)(2)Pb5I14*2I(2) (1) and (C8H11S)(2)Pb2I6*I-2 (2), have been synthesized and subsequently characterized in this study. The materials were synthesized from facile one-pot, one-step reactions of lead iodide, corresponding sulfide, methanol, iodine, and hydroiodic acid in the case of 2. Structural analysis reveals the presence of polyiodide entities in both compounds. Compound 1 contains triiodide anions, I-3(-), that are uniquely shared between the 2D inorganic slabs, forming a 3D network. Both 1 and 2 have I-2 molecules that are bridging the inorganic slabs through a structural motif that can be regarded as a tetraiodide anion, I-4(2-). Optical spectroscopy shows band gaps of 1.86 eV for 1 and 1.89 eV for 2. The optoelectronic properties were further investigated with band structure calculations. Single-crystal IV-characteristics of 1 show that the compound is photoactive confirming it as a promising photovoltaic candidate. Compound 1 highlights a novel strategy of designing 3D semiconducting hybrid materials by incorporating polyiodides to provide direct geometric and electronic connections between the semiconducting inorganic perovskite sheets.