Design and Synthesis of Small Molecules for Organic and Grätzel Solar Cells

El creixement de la població i dels nous països emergents fa que el consum energètic es dispari. Tota la població depèn d’aquest consum i com a conseqüència es depèn de les reserves de combustibles fòssils disponibles. Una de les fonts d’energia no esgotable i que proveu a la terra d’una gran quantitat d’energia es el Sol. Aquesta Energia ja està sent explotada amb la utilització de panells solars basades en silici. No obstant degut al seu alt cost de fabricació no poden competir amb les fonts d’energia ja existents. Per tant, noves investigacions en alternatives han estat àmpliament estudiades. Unes de les alternatives que han estat àmpliament estudiades durant aquests anys han estat les cel·les sensitivitzades amb colorant (DSSC) i les cel·les orgàniques (OPV). Les bases i el funcionament d’aquests dos tipus de dispositius es mostren en el capítol 1. El principal estudi d’aquesta tesis es centra en el disseny i la síntesis de nous colorants per aquest tipus de dispositius. Aquests colorants tenen un paper molt important en aquests dispositius i moltes vegades la seva eficiència deriva de l’estructura d’aquests colorants degut a les reaccions que es produeixen en els dispositius. En el Capítol 3 i 4 es presenta el disseny de dos tipus de colorants pel que fa a les cel·les sensitivitzades amb colorant (DSSC). En el capítol 3 es tracta de noves molècules orgàniques amb estructura D-π-A àmpliament estudiades com a alternativa als complexes de ruteni. En el capítol 4 les molècules sintetitzades també per DSSC són una família de porfirines, les quals són les que actualment estan mostrant més eficiència. Per una altra banda en el capítol 5 s’ha sintetitzat també una porfirina però en aquest cas per estudiar la seva aplicabilitat en les cel·les solars orgàniques (OPV).El Crecimiento de la población I de nuevos países emergentes hace que el consume energético se dispare. Toda la población depende de este consume I como consecuencia se depende de las reservas de combustibles fósiles disponibles. Una de las Fuentes de energía no agotable y que suministra a la tierra de una gran cantidad de energía es el Sol. Esta energía ya está siendo explotada con la utilización de paneles solares basados en Silicio. Sin embargo, debido a su elevado coste de fabricación no pueden competir con fuentes de energía ya existentes. Por lo tanto, nuevas investigaciones en alternativas han estado estudiadas. Una de las alternativas que han sido más estudiadas son las Celdas sensitibizadas con colorante (DSSC) i las Celdas Orgánicas (OPV). Las bases y su funcionamiento se muestran en el capítulo 1. El principal estudio de esta tesis se centra en el diseño y la síntesis de nuevos colorantes para estos tipos de dispositivos. Estos colorantes tienen un papel muy importante en estos dispositivos y muchas veces su eficiencia deriva de la estructura del colorante debido a reacciones que se producen en el dispositivo. En el Capítulo 3 y 4 se presenta el diseño de dos tipos de colorantes para las celdas sensitibizadas con colorante. En el Capítulo 3 se muestran moléculas orgánicas con estructura D--A que han sido ampliamente estudiadas como alternativa a los complejos de rutenio. En el capítulo 4 una familia de porfirinas ha sido sintetizada debido a los prometedores resultados mostrados siendo en la actualidad las moléculas que dan más eficiencia. En el Capítulo 5 en cambio se ha sintetizado una porfirina, pero en este caso para estudiar su aplicabilidad en las celdas orgánicas (OPV)The population is growing and the consumption of energy is dramatically increasing. All the population depends on this energy and are using fossil fuels available. One of this renewable source that gives to the earth a huge amount of energy is the sun. This source is exploited nowadays with photovoltaic devices based in silicon. However due to their high cost of production is not an alternative comparing with the existent sources. For this reason scientists of the entire world are working hard in the development of alternative devices in order to reduce the cost, decrease the contamination and increase the efficiencies among others. Some of alternatives that have been widely studied during the last years have been the Dye Sensitized Solar Cells (DSSC) and Organic Solar Cells (OPV). Basic principles of these devices are showed in Chapter 1. Principally the study of this thesis was focused in the design and synthesis of new sensitizers for these devices. These sensitizers play an important role in these devices and many times their structure depends on the efficiency of the device. In Chapter 3 and 4 the design and synthesis of two kinds of sensitizers and their applicability in DSSC is showed. In chapter 3 the sensitizers are organic dyes with a structure of D-π-A widely studied as alternative to the ruthenium complexes. In chapter 4 another family of sensitizers have been synthesized and also their applicability in DSSC has been studied. In this chapter the molecules are a family of porphyrins that are the molecules that nowadays are showing the most efficiency. On the other hand in Chapter 5 a new porphyrin has been synthesized but in this case to study their applicability in Organic solar Cells (OPV

Diarylamino-substituted Tetraarylethene (TAE) as Efficient and Robust Hole Transport Material for 11% Methyl Ammonium Lead Iodide Perovskite Solar Cells.

We report the synthesis and characterisation of tetra{4-[N,N-(4,4′-dimethoxydiphenylamino)]phenyl}ethene (TAE-1) as an efficient and robust hole transport material for its application in methyl ammonium lead iodide (MAPI) perovskite solar cells. The solar cells show light-to-energy conversion efficiencies as high as 11.0% under standard measurement conditions without the need of additional dopants

Synthesis, optical and electrochemical properties of the A–π-D–π-A porphyrin and its application as an electron donor in efficient solution processed

A conjugated acceptor&ndash;donor&ndash;acceptor (A&ndash;&pi;-D&ndash;&pi;-A) with the Zn-porphyrin core and the di-cyanovinyl substituted thiophene (A) connected at meso positions denoted as VC62 was designed and synthesized. The optical and electrochemical properties of VC62 were investigated. This new porphyrin exhibits a broad and intense absorption in the visible and near infrared regions. Bulk-heterojunction (BHJ) solution processed organic solar cells based on this porphyrin, as electron donor material, and PC71BM ([6,6]- phenyl C71 butyric acid methyl ester), as electron acceptor material, were fabricated using THF and a pyridine&ndash; THF solvent exhibiting a power conversion efficiency of 3.65% and 5.24%, respectively. The difference in efficiencies is due to the enhancement of the short circuit current Jsc and FF of the solar cell, which is ascribed to a stronger and broader incident photon to current efficiency (IPCE) response and a better balanced charge transport in the device processed with the pyridine&ndash;THF solvent</div

A single atom change “switches-on” the solar-to-energy conversion efficiency of Zn-porphyrin based dye sensitized solar cells to 10.5%

In this work we report how crucial is the correct design of the porphyrin sensitizers in Dye Sensitized Solar Cells (DSSCs). Only a single atom change switches-on the efficiency from 2&ndash;3% to over 10% under standard measurement conditions. We used the 2,1,3-benzothiadazole (BDT) group, as a p-conjugated linker, for the porphyrin LCVC01, a thiophene moiety for the porphyrin LCVC02 and also the furan group for the LCVC03 porphyrin, as molecular spacers between the BDT fragment and the molecule anchoring group, respectively. These three porphyrins were investigated for their application in DSSC devices. All the devices were characterized and found to achieve a record cell efficiency of 10.5% for LCVC02 but only 3.84% and 2.55% for LCVC01 and LCVC03 respectively. On one hand, the introduction of a thiophene, instead of a furan group, illustrates the importance of introducing a chemical group as a spacer, such as thiophene, between the BDT and the anchoring group. On the other hand, the selection of this group has to be correct because the change of a single atom increases the charge recombination rate and decreases the device performance. These changes can be rationalized by analyzing the dye dipoles and their interactions.</div

A single atom change “switches-on” the solar-to- energy conversion efficiency of Zn-porphyrin based dye sensitized solar cells to 10.5%

In this work we report how crucial is the correct design of the porphyrin sensitizers in Dye Sensitized Solar Cells (DSSCs). Only a single atom change switches-on the efficiency from 2–3% to over 10% under standard measurement conditions. We used the 2,1,3-benzothiadazole (BDT) group, as a p-conjugated linker, for the porphyrin LCVC01, a thiophene moiety for the porphyrin LCVC02 and also the furan group for the LCVC03 porphyrin, as molecular spacers between the BDT fragment and the molecule anchoring group, respectively. These three porphyrins were investigated for their application in DSSC devices. All the devices were characterized and found to achieve a record cell efficiency of 10.5% for LCVC02 but only 3.84% and 2.55% for LCVC01 and LCVC03 respectively. On one hand, the introduction of a thiophene, instead of a furan group, illustrates the importance of introducing a chemical group as a spacer, such as thiophene, between the BDT and the anchoring group. On the other hand, the selection of this group has to be correct because the change of a single atom increases the charge recombination rate and decreases the device performance. These changes can be rationalized by analyzing the dye dipoles and their interactions

Efficient bulk heterojunction solar cells based on solution processed small molecules based on the same benzo[1,2-b:4, 5-b’]thiophene unit as core don

We report the synthesis, characterization, and optical and electrochemical of properties of two novel molecules&nbsp;DRT3-BDT (1)&nbsp;and&nbsp;DTT3-BDT (2), comprising the same BDT central core (donor) and different end capped acceptor units,&nbsp;i.e.&nbsp;rhodanine with ethyl hexyl and thiazolidione with ethylhexyl, respectively, linked&nbsp;via&nbsp;an alkyl-substituted terthiophene (3 T) &pi;-conjugation bridge. The electrochemical properties of these small molecules indicate that their energy levels are compatible with energy levels of PC71BM for efficient exciton dissociation. These molecules have been used as electron donors along with PC71BM as an electron acceptor, for the fabrication of solution processed &ldquo;small molecule&rdquo; bulk heterojunction (BHJ) solar cells (smOPV). The device prepared from optimized&nbsp;1:PC71BM(1:1) processed cast from DIO (3%v)/CF solvent exhibited a power conversion efficiency of 6.76% with&nbsp;Jsc&nbsp;= 11.92 mA cm&minus;2,&nbsp;Voc&nbsp;= 0.90 and FF = 0.63. The device with&nbsp;2:PC71BM under the same conditions showed a lower PCE of 5.25% with&nbsp;Jsc&nbsp;= 10.52 mA cm&minus;2,&nbsp;Voc&nbsp;= 0.86 and FF = 0.56. The AFM, TEM and PL quenching measurements revealed that the high&nbsp;Jsc&nbsp;is a result of the appropriate morphology and exciton dissociation. The performances were compared for the devices based on two small molecules. The higher&nbsp;Jsc&nbsp;for device&nbsp;1&nbsp;was attributed to its better nanoscale phase separation, smooth surface and higher carrier mobility in the&nbsp;1:PC71BM blend film. Moreover, the higher value of FF for the&nbsp;1:PC71BM based device was ascribed to a good balance between the electron and hole mobilities. &nbsp; <img alt="Graphical abstract: Efficient bulk heterojunction solar cells based on solution processed small molecules based on the same benzo[1,2-b:4, 5-b′]thiophene unit as core donor and different terminal units" id="imgGALoader" src="http://pubs.rsc.org/services/images/RSCpubs.ePlatform.Service.FreeContent.ImageService.svc/ImageService/image/GA?id=C5NR01037C" style="border: 0px;" title="Gra

Solution processed organic solar cells based on A– D–D0–D–A small molecule with benzo[1,2-b:4,5-b0] dithiophene donor (D0) unit, cyclopentadithiophene

Solution processed small molecule A&ndash;D&ndash;D0&ndash;D&ndash;A, denoted as BDT(CDTRH)2, consists of 2-ethylhexoxy substituted BDT (donor D&#39; unit) as the central building block and 3-ethylrhodanine (RH) as the end capped terminal (acceptor group) unit, with a p-linkage of cyclopentadithiophene (CDT) (donor D). We have designed and synthesized it, and we have investigated its optical and electrochemical properties, finding that its energy levels are compatible with the energy levels of fullerene derivatives for efficient exciton dissociation. This small molecule has been used as an electron donor along with PC71BM as the electron acceptor for the fabrication of solution processed small molecule bulk heterojunction (BHJ) solar cells. The BHJ solar cell processed with BDT(CDTRH)2 : PC71BM (1 : 1 wt ratio) showed a power conversion efficiency (PCE) of 4.58% with Jsc &frac14; 8.66 mA cm_x0002_2, Voc &frac14; 0.98 V and FF &frac14; 0.54. The high Voc value of the device has been attributed to the deeper HOMO energy level of BDT(CDTRH)2. The overall PCE of the device has been increased up to 6.02% (Jsc &frac14; 10.42 mA cm_x0002_2, Voc &frac14; 0.94 V FF &frac14; 0.62) when the blend was processed with 3% v/v CN/CF solvent. This increase is mainly due to an increase in Jsc and FF, which was linked to the increase in crystallinity and favorable nanomorphology of the active layer improving exciton dissociation and achieving a more balanced charge transport in the device.</div

Selective Organic Contacts for Methyl Ammonium Lead Iodide (MAPI) Perovskite Solar Cells: Influence of Layer Thickness on Carriers Extraction and Carriers Lifetime

We have fabricated MAPI solar cells using as selective contacts PEDOT:PSS polymer for holes and PCBM-C70 fullerene derivative for electrons. The thickness of MAPI, PCBM-C70, and PEDOT:PSS layers has been varied in order to evaluate the contribution of each layer to the final device performance. We have measured the devices capacitance under illumination and the charge carrier’s lifetime using photoinduced time-resolved techniques. The results show that in this kind of devices the limiting layer is the PCBM-C70 due to its relative reduced mobility compared to PEDOT:PSS that makes the control of the fullerene thickness crucial for device optimization. Moreover, capacitive measurements show differences for the devices having different PCBM-C70 layer thicknesses in contrast with the measurements on the different PEDOT:PSS thickness. These give indications about holes and electrons storage and their distribution

A–p–D–p–A based porphyrin for solution processed small molecule bulk heterojunction solar cells

In this article, we have designed and synthesized a porphyrin with the following molecular architecture A&ndash; p&ndash;D&ndash;p&ndash;A in which ethyl rhodanine end capping groups were linked to the core porphyrin donor via an octyl thiophene-ethynylene p bridge denoted as VC117 and used it as an electron donor along with ([6,6]-phenyl C71 butyric acid methyl ester) (PC71BM) as an electron acceptor for the fabrication of solution processed organic solar cells. The solution processed BHJ organic solar cell with an optimized weight ratio of 1 : 1 VC117 : PC71BM in THF (tetrahydrofuran) showed an overall power conversion efficiency (PCE) of 2.95% with short circuit current Jsc &frac14; 8.34 mA cm_x0002_2, open circuit voltage Voc &frac14; 0.82 V and fill factor FF &frac14; 0.43. Nonetheless, when the active layer of the solar cell was processed from a mixture of 4% v/v of pyridine in THF solvent, it achieved a PCE value of 4.46% and further improved up to 5.50% after thermal annealing. This is ascribed to the enhancement of both the Jsc and FF values. The higher value of Jsc is explained by the increased absorption profile of the blend, the higher incident photon to current efficiency (IPCE) response and the better crystallinity of the active layer when processed with solvent additives and thermal annealing while the enhancement of FF is due to the better charge transport capability and the charge collection efficiency of the latter device.</div