Strain Engineering and Halogen Compensation of Buried Interface in Polycrystalline Halide Perovskites.

Inverted perovskite solar cells based on weakly polarized hole-transporting layers suffer from the problem of polarity mismatch with the perovskite precursor solution, resulting in a nonideal wetting surface. In addition to the bottom-up growth of the polycrystalline halide perovskite, this will inevitably worse the effects of residual strain and heterogeneity at the buried interface on the interfacial carrier transport and localized compositional deficiency. Here, we propose a multifunctional hybrid pre-embedding strategy to improve substrate wettability and address unfavorable strain and heterogeneities. By exposing the buried interface, it was found that the residual strain of the perovskite films was markedly reduced because of the presence of organic polyelectrolyte and imidazolium salt, which not only realized the halogen compensation and the coordination of Pb2+ but also the buried interface morphology and defect recombination that were well regulated. Benefitting from the above advantages, the power conversion efficiency of the targeted inverted devices with a bandgap of 1.62 eV was 21.93% and outstanding intrinsic stability. In addition, this coembedding strategy can be extended to devices with a bandgap of 1.55 eV, and the champion device achieved a power conversion efficiency of 23.74%. In addition, the optimized perovskite solar cells retained 91% of their initial efficiency (960 h) when exposed to an ambient relative humidity of 20%, with a T80 of 680 h under heating aging at 65 °C, exhibiting elevated durability.

Self-Healing Behavior of the Metal Halide Perovskites and Photovoltaics.

Perovskite solar cells have achieved rapid progress in the new-generation photovoltaic field, but the commercialization lags behind owing to the device stability issue under operational conditions. Ultimately, the instability issue is attributed to the soft lattice of ionic perovskite crystal. In brief, metal halide perovskite materials are susceptible to structural instability processes, including phase segregation, component loss, lattice distortion, and fatigue failure under harsh external stimuli such as high humidity, strong irradiation, wide thermal cycles, and large stress. Developing self-healing perovskites to further improve the unsatisfactory operational stability of their photoelectric devices under harsh stimuli has become a cutting-edge hotspot in this field. This self-healing behavior needs to be studied more comprehensively. Therefore, the self-healing behavior of the metal halide perovskites and photovoltaics is classified and summarized in this review. By discussing recent advances, underlying mechanisms, strategies, and existing challenges, this review provides perspectives on self-healing of perovskite solar cells in the future.

Poly(3-hexylthiophene)/perovskite Heterointerface by Spinodal Decomposition Enabling Efficient and Stable Perovskite Solar Cells.

The best research-cell efficiency of perovskite solar cells (PSCs) is comparable with that of mature silicon solar cells (SSCs); However, the industrial development of PSCs lags far behind SSCs. PSC is a multiphase and multicomponent system, whose consequent interfacial energy loss and carrier loss seriously affect the performance and stability of devices. Here, by using spinodal decomposition, a spontaneous solid phase segregation process, in situ introduces a poly(3-hexylthiophene)/perovskite (P3HT/PVK) heterointerface with interpenetrating structure in PSCs. The P3HT/PVK heterointerface tunes the energy alignment, thereby reducing the energy loss at the interface; The P3HT/PVK interpenetrating structure bridges a transport channel, thus decreasing the carrier loss at the interface. The simultaneous mitigation of energy and carrier losses by P3HT/PVK heterointerface enables n-i-p geometry device a power conversion efficiency of 24.53% (certified 23.94%) and excellent stability. These findings demonstrate an ingenious strategy to optimize the performance of PSCs by heterointerface via Spinodal decomposition.

Perovskite Solar Cells for Space Applications: Progress and Challenges.

Metal halide perovskites have aroused burgeoning interest in the field of photovoltaics owing to their versatile optoelectronic properties. The outstanding power conversion efficiency, high specific power (i.e., power to weight ratio), compatibility with flexible substrates, and excellent radiation resistance of perovskite solar cells (PSCs) enable them to be a promising candidate for next-generation space photovoltaic technology. Nevertheless, compared with other practical space photovoltaics, such as silicon and III-V multi-junction compound solar cells, the research on PSCs for space applications is just in the infancy stage. Therefore, there are considerable interests in further strengthening relevant research from the perspective of both mechanism and technology. Consequently, the approaches used for and the consequences of PSCs for space applications are reviewed. This review provides an overview of recent progress in PSCs for space applications in terms of performance evolution and mechanism exploration of perovskite films and devices under space extreme environments.

Buried Interfaces in Halide Perovskite Photovoltaics.

Understanding the fundamental properties of buried interfaces in perovskite photovoltaics is of paramount importance to the enhancement of device efficiency and stability. Nevertheless, accessing buried interfaces poses a sizeable challenge because of their non-exposed feature. Herein, the mystery of the buried interface in full device stacks is deciphered by combining advanced in situ spectroscopy techniques with a facile lift-off strategy. By establishing the microstructure-property relations, the basic losses at the contact interfaces are systematically presented, and it is found that the buried interface losses induced by both the sub-microscale extended imperfections and lead-halide inhomogeneities are major roadblocks toward improvement of device performance. The losses can be considerably mitigated by the use of a passivation-molecule-assisted microstructural reconstruction, which unlocks the full potential for improving device performance. The findings open a new avenue to understanding performance losses and thus the design of new passivation strategies to remove imperfections at the top surfaces and buried interfaces of perovskite photovoltaics, resulting in substantial enhancement in device performance.

Superior Carrier Lifetimes Exceeding 6 µs in Polycrystalline Halide Perovskites.

Lead halide perovskite films have witnessed rapid progress in optoelectronic devices, whereas polycrystalline heterogeneities and serious native defects in films are still responsible for undesired recombination pathways, causing insufficient utilization of photon-generated charge carriers. Here, radiation-enhanced polycrystalline perovskite films with ultralong carrier lifetimes exceeding 6 µs and single-crystal-like electron-hole diffusion lengths of more than 5 µm are achieved. Prolongation of charge-carrier activities is attributed to the electronic structure regulation and the defect elimination at crystal boundaries in the perovskite with the introduction of phenylmethylammonium iodide. The introduced electron-rich anchor molecules around the host crystals prefer to fill the halide/organic vacancies at the boundaries, rather than form low-dimensional phases or be inserted into the original lattice. The weakening of the electron-phonon coupling and the excitonic features of the photogenerated carriers in the optimized films, which together contribute to the enhancement of carrier separation and transportation, are further confirmed. Finally the resultant perovskite films in fully operating solar cells with champion efficiency of 23.32% are validated and a minimum voltage deficit of 0.39 V is realized.

Green Solution-Bathing Process for Efficient Large-Area Planar Perovskite Solar Cells.

Perovskite solar cells (PSCs) toward practical application relies on high efficiency, long lifetime, low toxicity, and device up-scaling. To realize large-area PSCs, a green solution-bathing strategy is delivered to prepare high-performance PSCs. By utilizing 2-pentanol as a green solvent and formamidinium chloride (FACl) as a solute in the green solution-bathing process, perovskite films with enlarged grain sizes, improved crystallinity, and alleviated defect state density were obtained, resulting in the enhancement in the power conversion efficiency of PSCs. Coupled with 2-pentanol and FACl, both a champion efficiency of 21.03% for small cells (0.103 cm2) and an efficiency of over 18% for large size (1.00 cm2) were obtained based on the GSB process, which can outperform its counterpart made via the commonly used antisolvent-dropping method. In addition, a large perovskite film (5 cm × 5 cm) with obvious mirror effect was successfully prepared. Our innovative approach paves the way to promote device up-scaling of PSCs via an environmentally friendly technique.

Diindolotriazatruxene-Based Hole-Transporting Materials for High-Efficiency Planar Perovskite Solar Cells.

A novel set of hole-transporting materials (HTMs) based on π-extended diindolotriazatruxene (DIT) core structure with electron-rich methoxy-engineered functional groups were designed and synthesized via a facile two-step procedure. All compounds were afforded from inexpensive precursors without a complex purification process. Cyclic voltammograms indicate that the resulting HTMs exhibit suitable highest occupied molecular orbital (HOMO) energy levels, which facilitate efficient hole injection from the valence band of perovskites into the HOMO of DIT-based HTMs as confirmed by time-resolved photoluminescence. Notable power conversion efficiency of the planar perovskite solar cells with low-temperature device fabrication achieved 18.21% utilizing D2, which is competitive with the corresponding devices based on the common Spiro-OMeTAD-based HTMs. The results manifest that DIT-based compounds are promising HTMs for constructing high-efficiency planar perovskite solar cells with low-cost solution processing procedures.

Modification of TiO2 Nanoparticles with Organodiboron Molecules Inducing Stable Surface Ti3+ Complex.

As one of the most promising semiconductor oxide materials, titanium dioxide (TiO2) absorbs UV light but not visible light. To address this limitation, the introduction of Ti3+ defects represents a common strategy to render TiO2 visible-light responsive. Unfortunately, current hurdles in Ti3+ generation technologies impeded the widespread application of Ti3+ modified materials. Herein, we demonstrate a simple and mechanistically distinct approach to generating abundant surface-Ti3+ sites without leaving behind oxygen vacancy and sacrificing one-off electron donors. In particular, upon adsorption of organodiboron reagents onto TiO2 nanoparticles, spontaneous electron injection from the diboron-bound O2- site to adjacent Ti4+ site leads to an extremely stable blue surface Ti3+‒O-· complex. Notably, this defect generation protocol is also applicable to other semiconductor oxides including ZnO, SnO2, Nb2O5, and In2O3. Furthermore, the as-prepared photoelectronic device using this strategy affords 103-fold higher visible light response and the fabricated perovskite solar cell shows an enhanced performance.

Zn+-O- Dual-Spin Surface State Formation by Modification of ZnO Nanoparticles with Diboron Compounds.

ZnO semiconductor oxides are versatile functional materials that are used in photoelectronics, catalysis, sensing, etc. The Zn+-O- surface electronic states of semiconductor oxides were formed on the ZnO surface by Zn 4s and O 2p orbital coupling with the diboron compound's B 2p orbitals. The formation of spin-coupled surface states was based on the spin-orbit interaction on the interface, which has not been reported before. This shows that the semiconductor oxide's spin surface states can be modulated by regulating surface orbital energy. The Zn+-O- surface electronic states were confirmed by electron spin resonance results, which may help in expanding the fundamental research on spintronics modulation and quantum transport.

Diboron-Assisted Interfacial Defect Control Strategy for Highly Efficient Planar Perovskite Solar Cells.

Metal halide perovskite films are endowed with the nature of ions and polycrystallinity. Formamidinium iodide (FAI)-based perovskite films, which include large cations (FA) incorporated into the crystal lattice, are most likely to induce local defects due to the presence of the unreacted FAI species. Here, a diboron-assisted strategy is demonstrated to control the defects induced by the unreacted FAI both inside the grain boundaries and at the surface regions. The diboron compound (C12 H10 B2 O4 ) can selectively react with unreacted FAI, leading to reduced defect densities. Nonradiative recombination between a perovskite film and a hole-extraction layer is mitigated considerably after the introduction of the proposed approach and charge-carrier extraction is improved as well. A champion power conversion efficiency of 21.11% is therefore obtained with a stabilized power output of 20.83% at the maximum power point for planar perovskite solar cells. The optimized device also delivers negligible hysteresis effect under various scanning conditions. This approach paves a new way for mitigating defects and improving device performance.

Enhanced photovoltage for inverted planar heterojunction perovskite solar cells.

The highest power conversion efficiencies (PCEs) reported for perovskite solar cells (PSCs) with inverted planar structures are still inferior to those of PSCs with regular structures, mainly because of lower open-circuit voltages (Voc). Here we report a strategy to reduce nonradiative recombination for the inverted devices, based on a simple solution-processed secondary growth technique. This approach produces a wider bandgap top layer and a more n-type perovskite film, which mitigates nonradiative recombination, leading to an increase in Voc by up to 100 millivolts. We achieved a high Voc of 1.21 volts without sacrificing photocurrent, corresponding to a voltage deficit of 0.41 volts at a bandgap of 1.62 electron volts. This improvement led to a stabilized power output approaching 21% at the maximum power point.

Improved performance of a CoTe//AC asymmetric supercapacitor using a redox additive aqueous electrolyte.

Cobalt telluride (CoTe) nanosheets as supercapacitor electrode materials are grown on carbon fiber paper (CFP) by a facile hydrothermal process. The CoTe electrode exhibits significant pseudo-capacitive properties with a highest C m of 622.8 F g-1 at 1 A g-1 and remarkable cycle stability. A new asymmetric supercapacitor (ASC) is assembled based on CoTe (positive electrode) and activated carbon (negative electrode), which can expand the operating voltage to as high as 1.6 V, and has a specific capacitance of 67.3 F g-1 with an energy density of 23.5 W h kg-1 at 1 A g-1. The performance of the ASC can be improved by introducing redox additive K4Fe(CN)6 into alkaline electrolyte (KOH). The results indicate that the ASC with K4Fe(CN)6 exhibits an ultrahigh specific capacitance of 192.1 F g-1 and an energy density of 67.0 W h kg-1, which is nearly a threefold increase over the ASC with pristine electrolyte.

Modulated CH3NH3PbI3-xBrx film for efficient perovskite solar cells exceeding 18.

The organic-inorganic lead halide perovskite layer is a crucial factor for the high performance perovskite solar cell (PSC). We introduce CH3NH3Br in the precursor solution to prepare CH3NH3PbI3-xBrx hybrid perovskite, and an uniform perovskite layer with improved crystallinity and apparent grain contour is obtained, resulting in the significant improvement of photovoltaic performance of PSCs. The effects of CH3NH3Br on the perovskite morphology, crystallinity, absorption property, charge carrier dynamics and device characteristics are discussed, and the improvement of open circuit voltage of the device depended on Br doping is confirmed. Based on above, the device based on CH3NH3PbI2.86Br0.14 exhibits a champion power conversion efficiency (PCE) of 18.02%. This study represents an efficient method for high-performance perovskite solar cell by modulating CH3NH3PbI3-xBrx film.

TiO2 quantum dots as superb compact block layers for high-performance CH3NH3PbI3 perovskite solar cells with an efficiency of 16.97.

A compact TiO(2) layer is crucial to achieve high-efficiency perovskite solar cells. In this study, we developed a facile, low-cost and efficient method to fabricate a pinhole-free and ultrathin blocking layer based on highly crystallized TiO(2) quantum dots (QDs) with an average diameter of 3.6 nm. The surface morphology of the blocking layer and the photoelectric performance of the perovskite solar cells were investigated by spin-coating with three different materials: colloidal TiO(2) QDs, titanium precursor solution, and aqueous TiCl(4). Among these three treatments, the perovskite solar cell based on the TiO(2) QD compact layer offered the highest power conversion efficiency (PCE) of 16.97% with a photocurrent density of 22.48 mA cm(-2), a photovoltage of 1.063 V and a fill factor of 0.71. The enhancement of PCE mainly stems from the small series resistance and the large shunt resistance of the TiO(2) QD layer.