Search

Mixed tin/lead (Sn/Pb) perovskites have the potential to achieve higher performances in single junction solar cells compared to Pb-based compounds. The best Sn/Pb based devices are fabricated in a p-i-n structure, and PEDOT:PSS is frequently utilized as the hole transport layer, even if there are many doubts on a possible detrimental role of this conductive polymer. Here, we propose the use of [2-(9H-carbazol-9-yl)ethyl]phosphonic acid (2PACz) and [2-(3, 6-dibromo-9H-carbazol-9-yl) ethyl] phosphonic acid (Br-2PACz) as substitutes for PEDOT:PSS. By using Cs(0.25)FA(0.75)Sn(0.5)Pb(0.5)I(3) as the active layer, we obtained record efficiencies as high as 19.51% on Br-2PACz, while 18.44% and 16.33% efficiencies were obtained using 2PACz and PEDOT:PSS, respectively. In addition, the implemented monolayers enhance both the shelf lifetime of the device as well as the operational stability. Finally, the Br-2PACz-based devices maintained 80% of their initial efficiency under continuous illumination for 230 h, and after being stored in a N-2 atmosphere for 4224 h (176 days).

Bromide-based perovskites have large bandgaps, making them attractive for tandem solar cells developed to overcome the Shockley–Queisser limit. A perovskite solar cell architecture employs transporting layers to improve charge extraction and transport. Due to the wide variety of materials and preparation methods, it is critical to devise fast screening methods to rank transporting layers. Herein, we evaluate perovskite fluorescence quenching followed by time- and energy-resolved photoluminescence (TER-PL) and analyse the intensity dependence as a potential method to qualify charge-transporting layers rapidly. The capability of the technique was evaluated with TiO2/FAPbBr3 and SnO2/FAPbBr3, the most commonly used electron transporting layers, which were prepared using standard protocols to make best-performing devices. The results revealed that TiO2 is the most effective quencher due to the higher density of states in the conduction band, consistent with Marcus-Gerischer's theory. However, record-performance devices use SnO2 as the electron transport layer. This shows that the relationship between photoluminescence quenching and device performance is not bidirectional. Therefore, additional measurements like conductivity are also needed to provide reliable feedback for device performance.

High band gap FAPbBr(3) perovskite solar cellshave attractedtremendous interest in recent years due to the high open circuit voltageand good stability. Commonly a two-step method is used to preparethe FAPbBr(3) perovskite film. Here a mixed solvent approachfor the second step is introduced. Formamidinium bromide (FABr) in2-propanol and methanol mixture was applied in the second step, whichresulted in favorable properties such as suitable solubility, high-qualitycrystallization, large grain size, improved charge extraction properties,and suppressed non-radiative recombination processes, and furtherenhance the power conversion efficiency (PCE) from 4.06 to 7.87%.As previously reported, methylammonium chloride (MACl) can help toimprove the morphology and crystallinity of perovskite. To furtherprove the versatility of such a mixed solvent strategy and enhancethe photovoltage performance, a small amount of MACl was added tothe FABr solution with mixed solvents, and a high PCE of 9.23% wasachieved under ambient conditions.

Lead halide perovskitesolar cells have reached power conversionefficiencies during the past few years that rival those of crystallinesilicon solar cells, and there is a concentrated effort to commercializethem. The use of gold electrodes, the current standard, is prohibitivelycostly for commercial application. Copper is a promising low-costelectrode material that has shown good stability in perovskite solarcells with selective contacts. Furthermore, it has the potential tobe self-passivating through the formation of CuI, a copper salt whichis also used as a hole selective material. Based on these opportunities,we investigated the interface reactions between lead halide perovskitesand copper in this work. Specifically, copper was deposited on theperovskite surface, and the reactions were followed in detail usingsynchrotron-based and in-house photoelectron spectroscopy. The resultsshow a rich interfacial chemistry with reactions starting upon depositionand, with the exposure to oxygen and moisture, progress over manyweeks, resulting in significant degradation of both the copper andthe perovskite. The degradation results not only in the formationof CuI, as expected, but also in the formation of two previously unreporteddegradation products. The hope is that a deeper understanding of theseprocesses will aid in the design of corrosion-resistant copper-basedelectrodes.

In this work, the photovoltaic performance and stability of perovskite solar cells (PSCs) based on a dopant-free hole transport layer (HTL) are efficiently improved by inserting a two-dimensional (2D) interfacial layer. The benzyl ammonium lead iodide (BA2PbI4) 2D perovskite is used as an interfacial layer between the 3D CH3NH3PbI3 perovskite and two moisture-resistant dopant-free HTLs including poly[[2,3-bis(3-octyloxyphenyl)-5,8-quinoxalinediyl]-2,5-thiophenediyl] (TQ1) and poly(3-hexylthiophene) (P3HT). TQ1 with a facile synthesis procedure has a higher moisture resistivity compared to P3HT which can improve the stability of PSCs. The 2D BA2PbI4 perovskite with a less-volatile bulkier organic cation efficiently passivates the defects at the perovskite/HTL interface, leading to 11.95% and 15.04% efficiency for the modified TQ1 and P3HT based cells, respectively. For a better understanding, the structural, optical, and electrical properties of PSCs comprising P3HT and TQ1 HTLs with and without interface modification are studied. The interface modified PSCs show slower open-circuit voltage decay and longer carrier lifetimes compared to unmodified cells. In addition, impedance spectroscopy reveals lower charge transport resistance and higher recombination resistance for the modified devices, which could be associated with the modification of the interface between the 3D CH3NH3PbI3 perovskite and HTL caused by the 2D interfacial layer. Also after aging under ambient conditions for about 800 hours, the modified PCSs retain more than 80% of their initial PCEs. These results give us the hope of achieving simpler, cheaper, and more stable PSCs with dopant-free HTLs through 2D interfacial layers, which have great potential for commercialization., Title in Web of Science: Enhancing the efficiency and stability of perovskite solar cells based on moisture-resistant dopant free hole transport materials by using a 2D-BA(2)PbI(4) interfacial layer

This roadmap on Nanotechnology for Catalysis and Solar Energy Conversion focuses on the application of nanotechnology in addressing the current challenges of energy conversion: 'high efficiency, stability, safety, and the potential for low-cost/scalable manufacturing' to quote from the contributed article by Nathan Lewis. This roadmap focuses on solar-to-fuel conversion, solar water splitting, solar photovoltaics and bio-catalysis. It includes dye-sensitized solar cells (DSSCs), perovskite solar cells, and organic photovoltaics. Smart engineering of colloidal quantum materials and nanostructured electrodes will improve solar-to-fuel conversion efficiency, as described in the articles by Waiskopf and Banin and Meyer. Semiconductor nanoparticles will also improve solar energy conversion efficiency, as discussed by Boschloo et al in their article on DSSCs. Perovskite solar cells have advanced rapidly in recent years, including new ideas on 2D and 3D hybrid halide perovskites, as described by Spanopoulos et al 'Next generation' solar cells using multiple exciton generation (MEG) from hot carriers, described in the article by Nozik and Beard, could lead to remarkable improvement in photovoltaic efficiency by using quantization effects in semiconductor nanostructures (quantum dots, wires or wells). These challenges will not be met without simultaneous improvement in nanoscale characterization methods. Terahertz spectroscopy, discussed in the article by Milot et al is one example of a method that is overcoming the difficulties associated with nanoscale materials characterization by avoiding electrical contacts to nanoparticles, allowing characterization during device operation, and enabling characterization of a single nanoparticle. Besides experimental advances, computational science is also meeting the challenges of nanomaterials synthesis. The article by Kohlstedt and Schatz discusses the computational frameworks being used to predict structure-property relationships in

Lead halide perovskite quantum dots (PQDs), also called perovskite nanocrystals, are considered as one of the most promising classes of photovoltaic materials for solar cells due to their prominent optoelectronic properties and simple preparation techniques. Remarkable achievements in PQD solar cells (PQDSCs) have been made. In particular, the power conversion efficiency of PQDSCs has been largely pushed from 10.77% to 17.39% (certified 16.6%) by finely controlling the surface chemistry of PQDs and the device physics of PQDSCs. In this review, we summarize the latest advances of emerging PQDSCs and discuss various strategies applied to improve the device performance of PQDSCs, including the synthesis methods, compositional engineering and surface chemistry of PQDs. Moreover, the device operation of PQDSCs is discussed to highlight the effect of device architecture on the photovoltaic performance of PQDSCs. Facing the practical applications of the PQDSCs under ambient conditions, device stability is also highlighted. Finally, conclusions and perspectives are presented along with the possible challenges and opportunities to promote development steps of PQDSCs with higher photovoltaic performance and robust stability.

Surface modification of perovskite films using a combination of 1-dodecanethiol (DT) and MoS2 nanosheets is investigated for perovskite solar cells. This surface modification is studied for two different types of perovskites, one with triple cations (CsFAMA) and one with double cations (FAMA), resulting in solar cell devices with power conversion efficiency (PCE) values of 18-19 and >20%, respectively. In both cases, stability enhancement is observed with DT and MoS2 surface modification using three different stability tracking protocols. The results reveal that by including DT and MoS2, the device retains 92% of its highest efficiency after 2200 h in dark (in air), while the standard device retained only 72%. Moreover, after light cycling, the device with DT and MoS2 retained 80%, and the standard device retained 55% of its maximum PCE. Moreover, these surface modifications gave rise to 58% decrease in the number of short-circuited devices and more reproducible results. Different characterizations revealed that the stability and efficiency enhancement is mainly due to reduced interface trap densities, improved charge transfer, and longer charge carrier lifetime. Moreover, the DT and MoS2 modifications induce hydrophobicity with an average contact angle over 80 degrees.

We present the synthesis and characterization of an efficient and low cost solar-driven electrolyzer consisting of Earth-abundant materials. The trimetallic NiFeMo electrocatalyst takes the shape of nanometer-sized flakes anchored to a fully carbon-based current collector comprising a nitrogen-doped carbon nanotube network, which in turn is grown on a carbon fiber paper support. This catalyst electrode contains solely Earth-abundant materials, and the carbon fiber support renders it effective despite a low metal content. Notably, a bifunctional catalyst-electrode pair exhibits a low total overpotential of 450 mV to drive a full water-splitting reaction at a current density of 10 mA cm(-2) and a measured hydrogen Faradaic efficiency of similar to 100%. We combine the catalyst-electrode pair with solution-processed perovskite solar cells to form a lightweight solar-driven water-splitting device with a high peak solar-to-fuel conversion efficiency of 13.8%.

Lead bromide perovskite with high bandgap and good stability has aroused broad interest for utilization in perovskite solar cells (PSCs) with high photovoltage, especially as a candidate for the front cell of tandem solar cells. However, the efficiency of lead bromide PSCs is still much lower than the standard lead iodide PSCs, and the defects in the perovskite are one of the main limiting factors hindering device performance. The construction of a 2D/3D perovskite interface is an effective way to passivate the interfacial defects and achieve efficient and stable PSCs. Herein, a facile and effective phenethylammonium bromide (PEABr) treatment method was applied to build a 2D/3D perovskite interface in FAPbBr(3) solar cells. An ultrathin layer of 2D PEA(2)PbBr(4) perovskite was successfully fabricated on the surface of 3D FAPbBr(3) perovskite by depositing the PEABr solution on the 3D perovskite films. The 2D perovskite layer significantly passivated the interfacial defects, leading to enhancement of power conversion efficiency from 7.7% to 9.4% and fill factor from 67.6% to 77.6%. Moreover, the hydrophobic alkyl chain in the PEA cation improved the moisture tolerance of the perovskite and significantly increases the solar cell stability. Additionally, the PEABr treatment strategy was successfully utilized for preparing semitransparent 2D/3D FAPbBr(3) perovskite solar cells.

Lead-free double perovskites, A2M+M′3+X6, are considered as promising alternatives to lead-halide perovskites, in optoelectronics applications. Although iodide (I) and bromide (Br) mixing is a versatile tool for bandgap tuning in lead perovskites, similar mixed I/Br double perovskite films have not been reported in double perovskites, which may be due to the large activation energy for ion migration. In this work, mixed Br/I double perovskites were realized utilizing an anion exchange method starting from Cs2AgBiBr6 solid thin-films with large grain-size. The optical and structural properties were studied experimentally and theoretically. Importantly, the halide exchange mechanism was investigated. Hydroiodic acid was the key factor to facilitate the halide exchange reaction, through a dissolution–recrystallization process. In addition, the common organic iodide salts could successfully perform halide-exchange while retaining high mixed-halide phase stability and strong light absorption capability.

In this work, four-terminal (4T) tandem solar cells were fabricated by using a methylammonium lead iodide (MAPbI3) perovskite solar cell (PSC) as the front-cell and a lead sulfide (PbS) colloidal quantum dot solar cell (CQDSC) as the back-cell. Different modifications of the tandem interlayer, at the interface between the sub-cells, were tested in order to improve the infrared transparency of the perovskite sub-cell and consequently increase the utilization of infrared (IR) light by the tandem system. This included the incorporation of a semi-transparent thin gold electrode (Au) on the MAPbI3 solar cell, followed by adding a molybdenum(VI) oxide (MoO3) layer or a surlyn layer. These interlayer modifications resulted in an increase of the IR transmittance to the back cell and improved the optical stability, compared to that in the reference devices. This investigation shows the importance of the interlayer, connecting the PSC with a strong absorption in the visible region and the CQDSC with a strong infrared absorption to obtain efficient next-generation tandem photovoltaics (PVs).

The p-type semiconducting colloidal quantum dot (CQD), working as a hole conductor in CQD solar cells (CQDSCs), is critical for charge carrier extraction and therefore, to large extent, determines the device's photovoltaic performance. However, during the preparation of a p-type CQD solid film on the top of an n-type CQD solid film, forming a p-n heterojunction within the CQDSCs, the optoelectronic properties of the underlayered n-type CQD solid film are significantly affected by conventional 1,2-ethanedithiol (EDT) ligands due to its high reactivity. Herein, a series of thiol ligands are comprehensively studied for p-type CQDs, which suggests that, by finely controlling the interaction between the CQDs and thiol ligands during the preparation of p-type CQD solid films, the n-type CQD solid films can be well protected and avoid destruction induced by thiol ligands. The p-type CQD solid film with 4-aminobenzenethiol (ABT) passivating the CQD surface exhibits better optoelectronic properties than the conventional p-type EDT-based CQD solid films, resulting in an improved photovoltaic performance in CQDSCs.

High-end organic–inorganic lead halide perovskite semitransparent p–i–n solar cells for tandem applications use a phenyl-C61-butyric acid methyl ester (PCBM)/atomic layer deposition (ALD)-SnOx electron transport layer stack. Omitting the PCBM would be preferred for manufacturing, but has in previous studies on (FA,MA)Pb(Br,I)3 and (Cs,FA)Pb(Br,I)3 and in this study on Cs0.05FA0.79MA0.16PbBr0.51I2.49 (perovskite) led to poor solar cell performance because of a bias-dependent light-generated current. A direct ALD-SnOx exposure was therefore suggested to form a nonideal perovskite/SnOx interface that acts as a transport barrier for the light-generated current. To further investigate the interface formation during the initial ALD SnOx growth on the perovskite, the mass dynamics of monitor crystals coated by partial p–i–n solar cell stacks were recorded in situ prior to and during the ALD using a quartz crystal microbalance. Two major finds were made. A mass loss was observed prior to ALD for growth temperatures above 60 °C, suggesting the decomposition of the perovskite. In addition, a mostly irreversible mass gain was observed during the first exposure to the Sn precursor tetrakis(dimethylamino)tin(IV) that is independent of growth temperature and that disrupts the mass gain of the following 20–50 ALD cycles. The chemical environments of the buried interface were analyzed by soft and hard X-ray photoelectron spectroscopy for a sample with 50 ALD cycles of SnOx on the perovskite. Although measurements on the perovskite bulk below and the SnOx film above did not show chemical changes, additional chemical states for Pb, Br, and N as well as a decrease in the amount of I were observed in the interfacial region. From the analysis, these states and not the heating of the perovskite were concluded to be the cause of the barrier. This strongly suggests that the detrimental effects can be avoided by controlling the interfacial design.

Energy efficient synthesis providing high quality crystalline thin films are highly desired in many applications. Here we devise a non-toxic solvent approach for production of highly crystalline MAPbI3 perovskite by exploiting diffusion aggregation processes. Isopropanol solution based methylammonium lead triiodide (MAPbI3) is used in this context, where the crystal growth initiation starts in an unstable suspension far from equilibrium and the subsequent crystallization is driven by the solubility parameters. The crystal formation is monitored by scanning transmission electron microscope (STEM), observing small crystallization centers growing as time evolves to large grains with high crystal purity. Energy dispersive X-ray spectroscopy (EDS) in STEM mode revealed a Pb rich core-shell structure in newly formed grains. Nano-beam Electron Diffraction (NBED) scan defined PbI2 crystallites in the Pb rich shell with a single crystal MAPbI3 core in newly formed grains. After a week stirring, the same aggregated suspension exhibited grains with only single crystal MAPbI3 structure. The NBED analysis shows a kinetically slow transition from a core shell structure to a single crystal grain. This research presents an impactful insight on the factors that may cause sub-stoichiometric grain boundary effects which can influence the solar cell performance. In addition, the structure, morphology and optical properties of the perovskite grains have been presented. A powder of highly crystalline particles was subsequently prepared by evaporation of the solvent in a low-vacuum oven. Thin film MAPbI3 solar cells were fabricated by dissolving the powder and applying it in a classical fabrication route. The MAPbI3 solar cells gave a champion efficiency of 20% (19.9%) and an average efficiency at approximately 17% with low hysteresis effects. Here a strategy to manufacture the material structure without toxic solvents is highlighted. The single-crystal growth devised here opens both for

This paper focuses on the development of 2-terminal CIGS-perovskite tandem solar cells by exploring a range of stack sequences and synthetic procedures for depositing the associated layers. In the end, we converged at a stack sequence composed of SLG/Mo/CIGS/CdS/i-ZnO/ZnO:Al/NiO/PTAA/Perovskite/LiF/PCBM/SnO2/ITO. With this architecture, we reached performances only about 1% lower than the corresponding 4-terminal tandem cells, thus demonstrating functional interconnects between the two sub-cells while grown monolithically on top of each other. We go through the stack, layer-by-layer, discussing their deposition and the results, from which we can conclude what works, what does not work, and what potentially could work after additional modifications. The challenges for a successful 2-terminal tandem device include: how to deal with, or decrease, the surface roughness of the CIGS-stack, how to obtain uniform coverage of the layers between the CIGS and the perovskite while also obtaining a benign interface chemistry, and how to tune the band gaps of both the CIGS and the perovskite to obtain good optical matching. The investigation was based on CIGS with a power conversion efficiency around 14%, and perovskites with an efficiency around 12%, resulting in 2-terminal tandem cells with efficiencies of 15–16%. The results indicate that by using higher performing CIGS and perovskite sub-cells, it should be possible to manufacture highly efficient 2-terminal CIGS-perovskite tandem devices by using the protocols, principles, and procedures developed and discussed in this paper.

Interface modification in perovskite solar cells is a key factor for achieving high power conversion efficiency by suppressing electron-hole recombination and accelerating charge carrier extraction. Here, we use a series of phenyl ammonium derivatives, phenyl ammonium iodide (PAI), benzyl ammonium iodide (BAI), and phenyl ethyl ammonium iodide (PEAI), to modify the interface between methylammonium lead triiodide (MAPbI3) perovskite and Spiro-OMeTAD as a hole transport layer in solar cell devices. The structural and optical properties of the perovskite films are studied and the results reveal the formation of two-dimensional perovskite interfacial layers on the surface of the MAPbI3 film modified with PEAI and BAI whereas the MAPbI3 layer modified with PAI gives an interface layer with slightly different properties compared to the two-dimensional perovskite. Impedance spectroscopy shows that the charge transport resistance of the interface engineered solar cells decreases when compared to pristine MAPbI3. In addition, slower open-circuit voltage decay and longer carrier lifetime are also observed for the modified cells which in total lead to the improvement of the photovoltaic performance. The investigation therefore gives insight in the effect of interface modifications, and especially how different sizes of the molecular interface modifier results in different interface formation and characteristics.

Silver bismuth iodide (Ag–Bi–I) light absorbers are interesting candidates as lead-free and low-toxic metal-halide materials for solar cell applications. In this work, the partial exchange of bismuth, Bi, with antimony, Sb, is investigated in samples prepared from a solution targeting stoichiometry AgBi2I7. Samples with a gradually increased exchange of Bi by Sb are prepared and light absorption measurements show that the absorption edge is gradually blue-shifted with increasing the amount of Sb. This trend in the shift in combination with the X-ray diffraction and X-ray photoelectron spectroscopy measurements, suggest that new materials with a mixture of Sb and Bi are formed. The density functional theory based electronic structure calculations reproduce the trend observed in the experiments when including spin–orbit coupling, which indicates the importance of relativistic effects in these materials. X-ray photoelectron spectroscopy is used to characterize the materials, and confirms the exchange of Bi to Sb in the samples. When Sb is included in the material, the grain size changes between 50 and 200 nm and the solar cell performance also changes. An optimal power conversion efficiency with excellent reproducibility and stability is obtained for a solar cell with the ratio of Sb/Bi equal to 3.

Lead halide perovskite solar cells have significantly increased in both efficiency and stability over the last decade. An important aspect of their longterm stability is the reaction between the perovskite and other materials in the solar cell. This includes the contact materials and their degradation if they can potentially come into contact through, e.g., pinholes or material diffusion and migration. Here, we explore the interactions of silver contacts with lead halide perovskites of different compositions by using a model system where thermally evaporated silver was deposited directly on the surface of the perovskites. Using X-ray photoelectron spectroscopy with support from scanning electron microscopy, X-ray diffraction, and UV-visible absorption spectroscopy, we studied the film formation and degradation of silver on perovskites with different compositions. The deposited silver does not form a continuous silver film but instead tends to form particles on a bare perovskite surface. These particles are initially metallic in character but degrade into AgI and AgBr over time. The degradation and migration appear unaffected by the replacement of methylammonium with cesium but are significantly slowed down by the complete replacement of iodide with bromide. The direct contact between silver and the perovskite also significantly accelerates the degradation of the perovskite, with a significant loss of organic cations and the possible formation of PbO, and, at the same time, changed the surface morphology of the iodide-rich perovskite interface. Our results further indicate that an important degradation pathway occurred through gas-phase perovskite degradation products. This highlights the importance of control over the interface materials and the use of completely hermetical barrier layers for the long-term stability and therefore the commercial viability of silver electrodes., QC 20200310