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Understanding the kinetic competition between charge extraction and recombination, and how this is impacted by mobile ions, remains a key challenge in perovskite solar cells (PSCs). Here, this issue is addressed by combining operando photoluminescence (PL) measurements, which allow the measurement of real‐time PL spectra during current–voltage (J–V) scans under 1‐sun equivalent illumination, with the results of drift‐diffusion simulations. This operando PL analysis allows direct comparison between the internal performance (recombination currents and quasi‐Fermi‐level‐splitting (QFLS)) and the external performance (J–V) of a PSC during operation. Analyses of four PSCs with different electron transport materials (ETMs) quantify how a deeper ETM LUMO induces greater interfacial recombination, while a shallower LUMO impedes charge extraction. Furthermore, it is found that a low ETM mobility leads to charge accumulation in the perovskite under short‐circuit conditions. However, thisalone cannot explain the remarkably high short‐circuit QFLS of over 1 eV which is observed in all devices. Instead, drift‐diffusion simulations allow this effect to be assigned to the presence of mobile ions which screen the internal electric field at short‐circuit and lead to a reduction in the short‐circuit current density by over 2 mA cm−2 in the best device. [ABSTRACT FROM AUTHOR]

High temperature post‐deposition annealing of hybrid lead halide perovskite thin films—typically lasting at least 10 min—dramatically limits the maximum roll‐to‐roll coating speed, which determines solar module manufacturing costs. While several approaches for "annealing‐free" perovskite solar cells (PSCs) have been demonstrated, many are of limited feasibility for scalable fabrication. Here, this work has solvent‐engineered a high vapor pressure solvent mixture of 2‐methoxy ethanol and tetrahydrofuran to deposit highly crystalline perovskite thin‐films at room temperature using gas‐quenching to remove the volatile solvents. Using this approach, this work demonstrates p‐i‐n devices with an annealing‐free MAPbI3 perovskite layer achieving stabilized power conversion efficiencies (PCEs) of up to 18.0%, compared to 18.4% for devices containing an annealed perovskite layer. This work then explores the deposition of self‐assembled molecules as the hole‐transporting layer without annealing. This work finally combines the methods to create fully annealing‐free devices having stabilized PCEs of up to 17.1%. This represents the state‐of‐the‐art for annealing‐free fabrication of PSCs with a process fully compatible with roll‐to‐roll manufacture. [ABSTRACT FROM AUTHOR]

Mixed‐halide perovskites offer ideal bandgaps for tandem solar cells, but photoinduced halide segregation compromises photovoltaic device performance. This study explores the influence of a hole‐transport layer, necessary for a full device, by monitoring halide segregation through in situ, concurrent X‐ray diffraction and photoluminescence measurements to disentangle compositional and optoelectronic changes. This work demonstrates that top coating FA0.83Cs0.17Pb(Br0.4I0.6)3 perovskite films with a poly(triaryl)amine (PTAA) hole‐extraction layer surprisingly leads to suppression of halide segregation because photogenerated charge carriers are rapidly trapped at interfacial defects that do not drive halide segregation. However, the generation of iodide‐enriched regions near the perovskite/PTAA interface enhances hole back‐transfer from the PTAA layer through improved energy level offsets, increasing radiative recombination losses. It is further found that while passivation with a piperidinium salt slows halide segregation in perovskite films, the addition of a PTAA top‐coating accelerates such effects, elucidating the specific nature of trap types that are able to drive the halide segregation process. This work highlights the importance of selective passivation techniques for achieving efficient and stable wide‐bandgap perovskite photovoltaic devices. [ABSTRACT FROM AUTHOR]

Perovskite semiconductors differ from most inorganic and organic semiconductors due to the presence of mobile ions in the material. Although the phenomenon is intensively investigated, important questions such as the exact impact of the mobile ions on the steady‐state power conversion efficiency (PCE) and stability remain. Herein, a simple method is proposed to estimate the efficiency loss due to mobile ions via "fast‐hysteresis" measurements by preventing the perturbation of mobile ions out of their equilibrium position at fast scan speeds (≈1000 V s−1). The "ion‐free" PCE is between 1% and 3% higher than the steady‐state PCE, demonstrating the importance of ion‐induced losses, even in cells with low levels of hysteresis at typical scan speeds (≈100 mV s−1). The hysteresis over many orders of magnitude in scan speed provides important information on the effective ion diffusion constant from the peak hysteresis position. The fast‐hysteresis measurements are corroborated by transient charge extraction and capacitance measurements and numerical simulations, which confirm the experimental findings and provide important insights into the charge carrier dynamics. The proposed method to quantify PCE losses due to field screening induced by mobile ions clarifies several important experimental observations and opens up a large range of future experiments. [ABSTRACT FROM AUTHOR]

Perovskite solar cells deliver high efficiencies, but are often made from high‐cost bespoke chemicals, such as the archetypical hole‐conductor, 2,2′,7,7′‐tetrakis(N,N‐di‐p‐methoxy‐phenylamine)‐9‐9′‐spirobifluorene (spiro‐OMeTAD). Herein, new charge‐transporting carbazole‐based enamine molecules are reported. The new hole conductors do not require chemical oxidation to reach high power conversion efficiencies (PCEs) when employed in n‐type‐intrinsic‐p‐type perovskite solar cells; thus, reducing the risk of moisture degrading the perovskite layer through the hydrophilicity of oxidizing additives that are typically used with conventional hole conductors. Devices made with these new undoped carbazole‐based enamines achieve comparable PCEs to those employing doped spiro‐OMeTAD, and greatly enhanced stability under 85 °C thermal aging; maintaining 83% of their peak efficiency after 1000 h, compared with spiro‐OMeTAD‐based devices that degrade to 26% of the peak PCE within 24 h. Furthermore, the carbazole‐based enamines can be synthesized without the use of organometallic catalysts and complicated purification techniques, lowering the material cost by one order of magnitude compared with spiro‐OMeTAD. As a result, we calculate that the overall manufacturing costs of future photovoltaic (PV) modules are reduced, making the levelized cost of electricity competitive with silicon PV modules. [ABSTRACT FROM AUTHOR]

Efficient mixed metal lead‐tin halide perovskites are essential for the development of all‐perovskite tandem solar cells, however they are currently limited by significant short‐circuit current losses despite their near optimal bandgap (≈1.25 eV). Herein, the origin of these losses is investigated, using a combination of voltage dependent photoluminescence (PL) timeseries and various charge extraction measurements. It is demonstrated that the Pb/Sn‐perovskite devices suffer from a reduction in the charge extraction efficiency within the first few seconds of operation, which leads to a loss in current and lower maximum power output. In addition, the emitted PL from the device rises on the exact same timescales due to the accumulation of electronic charges in the active layer. Using transient charge extraction measurements, it is shown that these observations cannot be explained by doping‐induced electronic charges but by the movement of mobile ions toward the perovskite/transport layer interfaces, which inhibits charge extraction due to band flattening. Finally, these findings are generalized to lead‐based perovskites, showing that the loss mechanism is universal. This elucidates the negative role mobile ions play in perovskite solar cells and paves a path toward understanding and mitigating a key loss mechanism. [ABSTRACT FROM AUTHOR]

This paper investigates the impact of microstructure on the degradation rate of methylammonium lead triiodide (MAPbI3) perovskite films upon exposure to light and oxygen. By comparing the oxygen induced degradation of perovskite films of different microstructure-fabricated using either a lead acetate trihydrate precursor or a solvent engineering technique-it is demonstrated that films with larger and more uniform grains and better electronic quality show a significantly reduced degradation compared to films with smaller, more irregular grains. The effect of degradation on the optical, compositional, and microstructural properties of the perovskite layers is characterized and it is demonstrated that oxygen induced degradation is initiated at the layer surface and grain boundaries. It is found that under illumination, irreversible degradation can occur at oxygen levels as low as 1%, suggesting that degradation can commence already during the device fabrication stage. Finally, this work establishes that improved thin-film microstructure, with large uniform grains and a low density of defects, is a prerequisite for enhanced stability necessary in order to make MAPbI3 a promising long lived and low cost alternative for future photovoltaic applications. [ABSTRACT FROM AUTHOR]

The remarkable optoelectronic properties of hybrid halide perovskite absorbers have, in the past years, made the perovskite solar cell one of the most promising emerging photovoltaic technologies. The charge collecting layers are essential parts of this type of solar cell. Carbon nanotubes have emerged as a potential candidate to take on this role. Equipped with a range of highly beneficial properties including excellent charge transport characteristics, chemical inertness, as well as mechanical robustness, carbon nanotubes are able to both efficiently extract photogenerated charges, and improve the resilience and stability of a perovskite solar cell. Here, a concise overview of the current state-of-the-art of perovskite solar cells, in which carbon nanotubes are incorporated as a charge conduction layer, is provided. [ABSTRACT FROM AUTHOR]

The majority of hole-transporting layers used in n-i-p perovskite solar cells contain 4- tert butylpyridine ( tBP). High power-conversion efficiencies and, in particular, good steady-state performance appears to be contingent on the inclusion of this additive. On the quest to improve the steady state efficiencies of the carbon nanotube-based hole-transporter system, this study has found that the presence of tBP results in an extraordinary improvement in the performance of these devices. By deconstructing a prototypical device and investigating the effect of tBP on each individual layer, the results of this study indicate that this performance enhancement must be due to a direct chemical interaction between tBP and the perovskite material. This study proposes that tBP serves to p-dope the perovskite layer and investigates this theory with poling and work function measurements. [ABSTRACT FROM AUTHOR]

Metal halide perovskites have emerged as one of the most promising materials for photovoltaics (PVs), with power conversion efficiency of over 22% already demonstrated. In order to compete with traditional crystalline silicon PV, cost and stability are equally important issues that need to be considered besides efficiency. Copper thiocyanate (CuSCN) is an interesting candidate to be used as an inexpensive, thermally stable p-type charge conducting material in perovskite solar cells. Here, we report 13% efficient perovskite solar cells employing CuSCN as the hole-transport material. We compare the stability of cells employing CuSCN with those employing the archetypical organic hole-transporter 2,2′,7,7′-Tetrakis (N,N-di-p-methoxyphenyl-amine) 9,9′-Spirobifluorene (Spiro-OMeTAD), under elevated temperature in ambient atmosphere. Surprisingly, we find that the devices employing CuSCN degrade faster under elevated temperatures than the devices employing Spiro-OMeTAD. We discover that an interfacial degradation mechanism occurs at the heterojunction between the perovskite absorber and the CuSCN, even in a dry nitrogen atmosphere, identifying the presence of a critical instability. Interestingly, with the additional coating of the completed cells with a thin film of insulating poly(methyl methacrylate) (PMMA), functioning as a rudimentary 'on-cell' encapsulation, we significantly alleviate this issue and deliver efficient perovskite solar cells which survive for more than 1000 hours at 85 °C in air with only 25% degradation in performance. Beyond identifying a critical area to address in order to enable CuSCN to be useful for long term operation in perovskite solar cells, our findings indicate that the role of the 'encapsulant' is to both keep the environment out, and keep degradation products within the cell. [ABSTRACT FROM AUTHOR]

Organic-inorganic lead halide perovskites are emerging materials for the next-generation photovoltaics. Lead halides are the most commonly used lead precursors for perovskite active layers. Recently, lead acetate (Pb(Ac)2) has shown its superiority as the potential replacement for traditional lead halides. Here, we demonstrate a strategy to improve the efficiency for the perovskite solar cell based on lead acetate precursor. We utilized methylammonium bromide as an additive in the Pb(Ac)2 and methylammonium iodide precursor solution, resulting in uniform, compact and pinhole-free perovskite films. We observed enhanced charge carrier extraction between the perovskite layer and charge collection layers and delivered a champion power conversion efficiency of 18.3% with a stabilized output efficiency of 17.6% at the maximum power point. The optimized devices also exhibited negligible current density-voltage ( J- V) hysteresis under the scanning conditions. [ABSTRACT FROM AUTHOR]

Block-copolymer templated chemical solution deposition is used to prepare mesoporous Nd-doped TiO2 electrodes for perovskite-based solar cells. X-ray diffraction and photothermal deflection spectroscopy show substitutional incorporation into the TiO2 crystal lattice for low Nd concentration, and increasing interstitial doping for higher concentrations. Substitutional Nd-doping leads to an increase in stability and performance of perovskite solar cells by eliminating defects and thus increasing electron transport and reducing charge recombination in the mesoporous TiO2. The optimized doping concentration of 0.3% Nd enables the preparation of perovskite solar cells with stabilized power conversion efficiency of >18%. [ABSTRACT FROM AUTHOR]

In recent years, there has been an unprecedented rise in the performance of metal halide perovskite solar cells. They are now in a position to compete on performance with traditional crystalline solar cells, and as such the most pressing questions concern the long term operational stability of this class of solar cell. Here, recent developments in understanding and overcoming stability concerns of metal halide perovskite solar cells are highlighted. An overview of possible instability issues due to electrical, atmospheric, heat, and light stresses is provided and the different implications to the most commonly used device architectures are discussed. [ABSTRACT FROM AUTHOR]

Organic-inorganic metal halide perovskite solar cells have emerged in the past few years to promise highly efficient photovoltaic devices at low costs. Here, temperature-sensitive core-shell Ag@TiO2 nanoparticles are successfully incorporated into perovskite solar cells through a low-temperature processing route, boosting the measured device efficiencies up to 16.3%. Experimental evidence is shown and a theoretical model is developed which predicts that the presence of highly polarizable nanoparticles enhances the radiative decay of excitons and increases the reabsorption of emitted radiation, representing a novel photon recycling scheme. The work elucidates the complicated subtle interactions between light and matter in plasmonic photovoltaic composites. Photonic and plasmonic schemes such as this may help to move highly efficient perovskite solar cells closer to the theoretical limiting efficiencies. [ABSTRACT FROM AUTHOR]

Reversible photo-induced performance deterioration is observed in mesoporous TiO2-containing devices in an inert environment. This phenomenon is correlated with the activation of deep trap sites due to astoichiometry of the metal oxide. Interestingly, in air, these defects can be passivated by oxygen adsorption. These results show that the doping of TiO2 with aluminium has a striking impact upon the density of sub-gap states and enhances the conductivity by orders of magnitude. Dye-sensitized and perovskite solar cells employing Al-doped TiO2 have increased device efficiencies and significantly enhanced operational device stability in inert atmospheres. This performance and stability enhancement is attributed to the substitutional incorporation of Al in the anatase lattice, 'permanently' passivating electronic trap sites in the bulk and at the surface of the TiO2. [ABSTRACT FROM AUTHOR]

Solution‐deposited‐converted perovskite solar cells are studied by converting PbI2 planar films into the phase pure, mixed‐halide perovskite (H3CNH3)PbI3‐xClx. These solar cells exhibit very high photovoltaic performance and close to unity internal incident photon‐to‐electron conversion. [ABSTRACT FROM AUTHOR]

In article number 1700977, Yana Vaynzof and co‐workers investigate how the MAPbI3 perovskite layer microstructure is affecting its stability upon exposure to oxygen and light. The authors show that the degradation process is initiated at the grain boundaries, demonstrating that devices whose active layer consists of larger, more uniform grains exhibit enhanced photovoltaic stability. [ABSTRACT FROM AUTHOR]

Methylammonium bromide is used as an additive in the lead acetate‐based precursor solution for perovskite solar cells by T. P. Russell, R. Zhu, and co‐workers on page 3508. This is found to significantly improved perovskite film quality and optoelectronic properties. The optimized device delivers a power conversion efficiency of 18.3%, holding promise for highly efficient perovskite solar cells. [ABSTRACT FROM AUTHOR]

Air stable electron transport organic semiconductor was employed in inverted perovskite solar cells as a possible alternative to derivatives of fullerene. • Diketopyrrolopyrrole derivative employed as n-channel semiconductor in OFET. • TDPP-CN 4 exhibited higher electron mobility and ambient stability than PCBM. • Air stable DPP based acceptor was further employed in inverted perovskite devices. • The devices could not display competitive performance as PCBM owing to deep LUMO level. One of the possible causes of degradation of perovskite solar cells is the instability of the electron transporting layer. In this regard, design of air stable electron transport organic semiconductors, compatible with perovskite energy levels presents challenges due to inherent vulnerability to traps, presumably originating due to water and/or oxygen. In this work, we demonstrate air stability of diketopyrrolopyrrole-based molecule (TDPP-CN 4) at ambient conditions and its application as electron transporting layer (ETL) in perovskite solar cells. We investigated electron mobility and air stability of TDPP-CN 4 by fabricating top-gate bottom-contact (TG-BC) thin film transistors and compared with PCBM at ambient conditions. Both TDPP-CN 4 and PCBM exhibit electron transport properties with mobility of 0.13 cm2 V−1 s−1 and 0.03 cm2 V−1 s−1 respectively. However, we found remarkable air stability of the TDPP-CN 4 in the OFET measurements under ambient conditions. These excellent properties of TDPP-CN 4 render them as potential ETL layer in inverted planar heterojunction perovskite solar cells. Our preliminary device studies show remarkable short-circuit current (J sc) ∼ 17.4 mA/cm2 with moderate open-circuit voltage (V oc) of 0.50 V. These results suggest that the electron mobility and air-stability of diketopyrrolopyrrole-based molecule hold a promise as ETL in perovskite solar cells at ambient conditions. [ABSTRACT FROM AUTHOR]

An ultrathin Al 2 O 3 film deposited on methylammonium lead triiodide (CH 3 NH 3 PbI 3 ) perovskite has the capability to suppress the carrier recombination process and improve the perovskite solar cells efficiency and stability. However, annealing at temperatures higher than 85 °C degrades the CH 3 NH 3 PbI 3 perovskite film. The X-ray photoelectron spectroscopy study performed in this work indicates that it is possible to grow Al 2 O 3 by atomic layer deposition on the perovskite at room temperature, however, besides pure Al 2 O 3 some OH groups are found and the creation of lead and iodine oxides at the Al 2 O 3 /CH 3 NH 3 PbI 3 interface takes place. [ABSTRACT FROM AUTHOR]

Perovskite solar cells represent an emerging and highly promising renewable energy technology. However, the most efficient perovskite solar cells critically depend on the use of lead. This represents a possible environmental concern potentially limiting the technologies' commercialization. Here, we demonstrate a facile recycling process for PbI 2 , the most common lead-based precursor in perovskite absorber material. The process uses only hot water to effectively extract lead from synthetic precursor mixes, plastic- and glass-based perovskites (92.6 – 100% efficiency after two extractions). When the hot extractant is cooled, crystalline PbI 2 in high purity (> 95.9%) precipitated with a high yield: from glass-based perovskites, the first cycle of extraction / precipitation was sufficient to recover 94.4 ± 5.6% of Pb, whereas a second cycle yielded another 10.0 ± 5.2% Pb, making the recovery quantitative. The solid extraction residue remaining is consequently deprived of metals and may thus be disposed as non-hazardous waste. Therefore, exploiting the highly temperature-dependent solubility of PbI 2 in water provides a straightforward, easy to implement way to efficiently extract lead from PSC at the end-of-life and deposit the extraction residues in a cost-effective manner, mitigating the potential risk of lead leaching at the perovskites' end-of-life. [Display omitted] • Water solubility of PbI 2 is highly temperature dependent, which was exploited for Pb recycling from perovskites. • Pb was fully extracted from different perovskites and PbI 2 recovered in pure form was made into a new perovskite layer. • The extracted perovskite residues were sufficiently depleted in metals to not qualify as hazardous materials. [ABSTRACT FROM AUTHOR]

Block-copolymer templated chemical solution deposition is used to prepare mesoporous Nd-doped TiO2 electrodes for perovskite-based solar cells. X-ray diffraction and photothermal deflection spectroscopy show substitutional incorporation into the TiO2 crystal lattice for low Nd concentration, and increasing interstitial doping for higher concentrations. Substitutional Nd-doping leads to an increase in stability and performance of perovskite solar cells by eliminating defects and thus increasing electron transport and reducing charge recombination in the mesoporous TiO2. The optimized doping concentration of 0.3% Nd enables the preparation of perovskite solar cells with stabilized power conversion efficiency of >18%. [ABSTRACT FROM AUTHOR]

The performance of perovskite solar cells has been progressing over the past few years and efficiency is likely to continue to increase. However, a negative aspect for the integration of perovskite solar cells in the built environment is that the color gamut available in these materials is very limited and does not cover the green-to-blue region of the visible spectrum, which has been a big selling point for organic photovoltaics. Here, we integrate a porous photonic crystal (PC) scaffold within the photoactive layer of an opaque perovskite solar cell following a bottom-up approach employing inexpensive and scalable liquid processing techniques. The photovoltaic devices presented herein show high efficiency with tunable color across the visible spectrum. This now imbues the perovskite solar cells with highly desirable properties for cladding in the built environment and encourages design of sustainable colorful buildings and iridescent electric vehicles as future power generation sources. [ABSTRACT FROM AUTHOR]

Reversible photo-induced performance deterioration is observed in mesoporous TiO2-containing devices in an inert environment. This phenomenon is correlated with the activation of deep trap sites due to astoichiometry of the metal oxide. Interestingly, in air, these defects can be passivated by oxygen adsorption. These results show that the doping of TiO2 with aluminium has a striking impact upon the density of sub-gap states and enhances the conductivity by orders of magnitude. Dye-sensitized and perovskite solar cells employing Al-doped TiO2 have increased device efficiencies and significantly enhanced operational device stability in inert atmospheres. This performance and stability enhancement is attributed to the substitutional incorporation of Al in the anatase lattice, 'permanently' passivating electronic trap sites in the bulk and at the surface of the TiO2. [ABSTRACT FROM AUTHOR]