Triarylamine-based polymers with different functional groups were synthetized as hole-transport m... more Triarylamine-based polymers with different functional groups were synthetized as hole-transport materials (HTMs) for perovskite solar cells (PSCs). The novel materials enabled efficient PSCs without the use of chemical doping (or additives) to enhance charge transport. Devices employing poly(triarylamine) with methylphenylethenyl functional groups (V873) showed a power conversion efficiency of 12.3 %, whereas widely used additive-free poly[bis(4-phenyl)(2,4,6-trimethylphenyl)amine] (PTAA) demonstrated 10.8 %. Notably, devices with V873 enabled stable PSCs under 1 sun illumination at maximum power point tracking for approximately 40 h at room temperature, and in the dark under elevated temperature (85 °C) for more than 140 h. This is in stark contrast to additive-containing devices, which degrade significantly within the same time frame. The results present remarkable progress towards stable PSC under real working conditions and industrial stress tests.
Controlling the morphology and surface passivation in perovskite solar cells is paramount in obta... more Controlling the morphology and surface passivation in perovskite solar cells is paramount in obtaining optimal optoelectronic properties. This study incorporates N-doped graphene nanosheets in the perovskite layer which simultaneously induce an improved morphology and surface passivation at the perovskite/spiro interface, resulting in enhancement in all photovoltaic parameters.
ABSTRACT Antimony-doped tin oxide (ATO) aerogels have been prepared as conductive scaffolds for T... more ABSTRACT Antimony-doped tin oxide (ATO) aerogels have been prepared as conductive scaffolds for TiO2 in dye-sensitized solar cells (DSCs). The high surface area, porosity and particle interconnectivity inherent to aerogels, and the conductivity and transparency of ATO make these structures attractive as porous electron collectors. Aerogels were prepared by sol-gel processing and supercritical drying of ATO containing varying amounts of Sb. These were coated with varying TiO2 layer thicknesses by atomic layer deposition, sensitized with an organic dye (D149), and made into DSC devices using iodide/triiodide (I-/I3-) and ferrocene/ferrocenium (Fc/Fc+) electrolytes. Scanning electron microscopy was used to study the morphological characteristics of the aerogel materials. The effect of ALD cycles on the dye adsorption was measured. Current-voltage characteristics were used to study device performance. We found that ATO aerogels with 15% Sb have improved performance over TiO2 and undoped tin oxide aerogel devices. DSC electron kinetics were studied by transient decay measurements to better understand the role of electron transport and lifetime in the performance of the devices.
Atomic layer deposition (ALD) is unsurpassed in its ability to create thin conformal coatings ove... more Atomic layer deposition (ALD) is unsurpassed in its ability to create thin conformal coatings over very rough and/or porous materials. Yet although the coating thickness on flat surfaces can be measured by ellipsometry, characterization of these coatings on rough surfaces is difficult. Here, two techniques are demonstrated to provide such characterization of ALD-coated TiO2 over mesoporous SnO2 aerogel films on glass substrates, and insights are gained as to the ALD process. First, X-ray photoelectron spectroscopy (XPS) is used to determine the coating thickness over the aerogel, and the results (0.04 nm/cycle) agree well with ellipsometry on flat surfaces up to a coating thickness limit of about 6 nm. Second, quantitative analysis of SEM images of the aerogel cross section is used to determine porosity and roughness, from which coating thickness can be inferred. The analysis reveals increasing porosity from the aerogel/air interface to the aerogel/substrate interface, indicating a thicker ALD coating near the air side, which is consistent with tortuous diffusion through the pores limiting access of ALD precursors to deeper parts of the film. SEM-derived porosity is generally useful in a thin film because bulk methods like nitrogen physisorption or mercury porosimetry are impractical for use with thin-film samples. Therefore, in this study SEM was also used to characterize quantitatively the morphologogical changes in SnO2 aerogel thin films due to doping with Sb. This study can be used as a methodology to understand morphological changes in different types of porous and/or rough materials.
Perovskite solar cells (PSCs) have now achieved efficiencies in excess of 22%, but very little is... more Perovskite solar cells (PSCs) have now achieved efficiencies in excess of 22%, but very little is known about their long-term stability under thermal stress. So far, stability reports have hinted at the importance of substituting the organic components, but little attention has been given to the metal contact. We investigated the stability of state-of-the-art PSCs with efficiencies exceeding 20%. Remarkably, we found that exposing PSCs to a temperature of 70 °C is enough to induce gold migration through the hole-transporting layer (HTL), spiro-MeOTAD, and into the perovskite material, which in turn severely affects the device performance metrics under working conditions. Importantly, we found that the main cause of irreversible degradation is not due to decomposition of the organic and hybrid perovskite layers. By introducing a Cr metal interlayer between the HTL and gold electrode, high-temperature-induced irreversible long-term losses are avoided. This key finding is essential in ...
Perovskite solar cells are one of the most promising photovoltaic technologies with their extraor... more Perovskite solar cells are one of the most promising photovoltaic technologies with their extraordinary progress in efficiency and the simple processes required to produce them. However, the frequent presence of a pronounced hysteresis in the current voltage characteristic of these devices arises concerns on the intrinsic stability of organo-metal halides, challenging the reliability of technology itself. Here, we show that n-doping of mesoporous TiO2 is accomplished by facile post treatment of the films with lithium salts. We demonstrate that the Li-doped TiO2 electrodes exhibit superior electronic properties, by reducing electronic trap states enabling faster electron transport. Perovskite solar cells prepared using the Li-doped films as scaffold to host the CH3NH3PbI3 light harvester produce substantially higher performances compared with undoped electrodes, improving the power conversion efficiency from 17 to over 19% with negligible hysteretic behaviour (lower than 0.3%).
Journal of the American Chemical Society, Jan 20, 2016
Lead halide perovskites have over the last few years attracted considerable interest as photo abs... more Lead halide perovskites have over the last few years attracted considerable interest as photo absorbers in PV-applications with record efficiencies now reaching 22 %. It has recently been found that not only the composition but also the precise stoichiometry is important for the device performance. Recent reports have, for example, demonstrated small amount of PbI2 in the perovskite films to be beneficial for the overall performance of both the standard perovskite, CH3NH3PbI3, as well as for the mixed perovskites (CH3NH3)x(CH(NH2)2)(1-x)PbBryI(3-y). In this work a broad range of characterization techniques including: X-ray diffraction (XRD), scanning electron microscopy (SEM), transmission electron microscopy (TEM), photo electron spectroscopy (PES), transient absorption spectroscopy (TAS), UV-VIS, electroluminescence (EL), photoluminescence (PL), and confocal PL-mapping have been used to further understand the importance of remnant PbI2 in perovskite solar cells. Our best devices w...
Advanced materials (Deerfield Beach, Fla.), Jan 28, 2016
Hybrid organic-inorganic perovskite materials have risen up as leading components for light harve... more Hybrid organic-inorganic perovskite materials have risen up as leading components for light harvesting applications. However, to date many questions are still open concerning the operation of perovskite solar cells (PSCs). A systematic analysis of the interplay among structural features, optoelectronic performance, and ionic movement behavior for FA0.83 MA0.17 Pb(I0.83 Br0.17 )3 PSCs is presented, which yield high power conversion efficiencies up to 20.8%.
Triarylamine-based polymers with different functional groups were synthetized as hole-transport m... more Triarylamine-based polymers with different functional groups were synthetized as hole-transport materials (HTMs) for perovskite solar cells (PSCs). The novel materials enabled efficient PSCs without the use of chemical doping (or additives) to enhance charge transport. Devices employing poly(triarylamine) with methylphenylethenyl functional groups (V873) showed a power conversion efficiency of 12.3 %, whereas widely used additive-free poly[bis(4-phenyl)(2,4,6-trimethylphenyl)amine] (PTAA) demonstrated 10.8 %. Notably, devices with V873 enabled stable PSCs under 1 sun illumination at maximum power point tracking for approximately 40 h at room temperature, and in the dark under elevated temperature (85 °C) for more than 140 h. This is in stark contrast to additive-containing devices, which degrade significantly within the same time frame. The results present remarkable progress towards stable PSC under real working conditions and industrial stress tests.
Controlling the morphology and surface passivation in perovskite solar cells is paramount in obta... more Controlling the morphology and surface passivation in perovskite solar cells is paramount in obtaining optimal optoelectronic properties. This study incorporates N-doped graphene nanosheets in the perovskite layer which simultaneously induce an improved morphology and surface passivation at the perovskite/spiro interface, resulting in enhancement in all photovoltaic parameters.
ABSTRACT Antimony-doped tin oxide (ATO) aerogels have been prepared as conductive scaffolds for T... more ABSTRACT Antimony-doped tin oxide (ATO) aerogels have been prepared as conductive scaffolds for TiO2 in dye-sensitized solar cells (DSCs). The high surface area, porosity and particle interconnectivity inherent to aerogels, and the conductivity and transparency of ATO make these structures attractive as porous electron collectors. Aerogels were prepared by sol-gel processing and supercritical drying of ATO containing varying amounts of Sb. These were coated with varying TiO2 layer thicknesses by atomic layer deposition, sensitized with an organic dye (D149), and made into DSC devices using iodide/triiodide (I-/I3-) and ferrocene/ferrocenium (Fc/Fc+) electrolytes. Scanning electron microscopy was used to study the morphological characteristics of the aerogel materials. The effect of ALD cycles on the dye adsorption was measured. Current-voltage characteristics were used to study device performance. We found that ATO aerogels with 15% Sb have improved performance over TiO2 and undoped tin oxide aerogel devices. DSC electron kinetics were studied by transient decay measurements to better understand the role of electron transport and lifetime in the performance of the devices.
Atomic layer deposition (ALD) is unsurpassed in its ability to create thin conformal coatings ove... more Atomic layer deposition (ALD) is unsurpassed in its ability to create thin conformal coatings over very rough and/or porous materials. Yet although the coating thickness on flat surfaces can be measured by ellipsometry, characterization of these coatings on rough surfaces is difficult. Here, two techniques are demonstrated to provide such characterization of ALD-coated TiO2 over mesoporous SnO2 aerogel films on glass substrates, and insights are gained as to the ALD process. First, X-ray photoelectron spectroscopy (XPS) is used to determine the coating thickness over the aerogel, and the results (0.04 nm/cycle) agree well with ellipsometry on flat surfaces up to a coating thickness limit of about 6 nm. Second, quantitative analysis of SEM images of the aerogel cross section is used to determine porosity and roughness, from which coating thickness can be inferred. The analysis reveals increasing porosity from the aerogel/air interface to the aerogel/substrate interface, indicating a thicker ALD coating near the air side, which is consistent with tortuous diffusion through the pores limiting access of ALD precursors to deeper parts of the film. SEM-derived porosity is generally useful in a thin film because bulk methods like nitrogen physisorption or mercury porosimetry are impractical for use with thin-film samples. Therefore, in this study SEM was also used to characterize quantitatively the morphologogical changes in SnO2 aerogel thin films due to doping with Sb. This study can be used as a methodology to understand morphological changes in different types of porous and/or rough materials.
Perovskite solar cells (PSCs) have now achieved efficiencies in excess of 22%, but very little is... more Perovskite solar cells (PSCs) have now achieved efficiencies in excess of 22%, but very little is known about their long-term stability under thermal stress. So far, stability reports have hinted at the importance of substituting the organic components, but little attention has been given to the metal contact. We investigated the stability of state-of-the-art PSCs with efficiencies exceeding 20%. Remarkably, we found that exposing PSCs to a temperature of 70 °C is enough to induce gold migration through the hole-transporting layer (HTL), spiro-MeOTAD, and into the perovskite material, which in turn severely affects the device performance metrics under working conditions. Importantly, we found that the main cause of irreversible degradation is not due to decomposition of the organic and hybrid perovskite layers. By introducing a Cr metal interlayer between the HTL and gold electrode, high-temperature-induced irreversible long-term losses are avoided. This key finding is essential in ...
Perovskite solar cells are one of the most promising photovoltaic technologies with their extraor... more Perovskite solar cells are one of the most promising photovoltaic technologies with their extraordinary progress in efficiency and the simple processes required to produce them. However, the frequent presence of a pronounced hysteresis in the current voltage characteristic of these devices arises concerns on the intrinsic stability of organo-metal halides, challenging the reliability of technology itself. Here, we show that n-doping of mesoporous TiO2 is accomplished by facile post treatment of the films with lithium salts. We demonstrate that the Li-doped TiO2 electrodes exhibit superior electronic properties, by reducing electronic trap states enabling faster electron transport. Perovskite solar cells prepared using the Li-doped films as scaffold to host the CH3NH3PbI3 light harvester produce substantially higher performances compared with undoped electrodes, improving the power conversion efficiency from 17 to over 19% with negligible hysteretic behaviour (lower than 0.3%).
Journal of the American Chemical Society, Jan 20, 2016
Lead halide perovskites have over the last few years attracted considerable interest as photo abs... more Lead halide perovskites have over the last few years attracted considerable interest as photo absorbers in PV-applications with record efficiencies now reaching 22 %. It has recently been found that not only the composition but also the precise stoichiometry is important for the device performance. Recent reports have, for example, demonstrated small amount of PbI2 in the perovskite films to be beneficial for the overall performance of both the standard perovskite, CH3NH3PbI3, as well as for the mixed perovskites (CH3NH3)x(CH(NH2)2)(1-x)PbBryI(3-y). In this work a broad range of characterization techniques including: X-ray diffraction (XRD), scanning electron microscopy (SEM), transmission electron microscopy (TEM), photo electron spectroscopy (PES), transient absorption spectroscopy (TAS), UV-VIS, electroluminescence (EL), photoluminescence (PL), and confocal PL-mapping have been used to further understand the importance of remnant PbI2 in perovskite solar cells. Our best devices w...
Advanced materials (Deerfield Beach, Fla.), Jan 28, 2016
Hybrid organic-inorganic perovskite materials have risen up as leading components for light harve... more Hybrid organic-inorganic perovskite materials have risen up as leading components for light harvesting applications. However, to date many questions are still open concerning the operation of perovskite solar cells (PSCs). A systematic analysis of the interplay among structural features, optoelectronic performance, and ionic movement behavior for FA0.83 MA0.17 Pb(I0.83 Br0.17 )3 PSCs is presented, which yield high power conversion efficiencies up to 20.8%.
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Papers by Juan-Pablo Correa-Baena