Potassium Incorporation for Enhanced Performance and Stability of Fully Inorganic Cesium Lead Halide Perovskite Solar Cells.

Polymer-Passivated Inorganic Cesium Lead Halide Perovskites for High-Voltage and High-Efficiency Solar Cells

Vacuum-sublimed inorganic cesium lead halide perovskite thin films are prepared and integrated in all-vacuum-deposited solar cells. Special care is taken to determine the stoichiometric balance of the sublimation precursors, which has great influence on the device performance. The mixed halide devices exhibit exceptional stabilized power conversion efficiency (11.8%) and promising thermal and long-term stabilities.

Organic–inorganic lead halide perovskite solar cells are regarded as one of the most promising technologies for the next generation of photovoltaics due to their high power conversion efficiency (PCE) and simple solution manufacturing. Among the different compositions, the formamidinium lead iodide (FAPbI3) photoactive phase has a bandgap of 1.4 eV, which enables the corresponding higher PCEs according to the Shockley–Queisser limit. However, the photoactive crystal phase of FAPbI3 is not stable at room temperature. The most high‐performing compositions to date have reduced this problem by incorporating the methylammonium (MA) cation into the FAPbI3 composition, although MA has poor stability at high temperatures and in humid environments, which can limit the lifetime of FAxMA1−xPbI3 films. CsxFA1−xPbI3 perovskites are also explored, but despite better stability they still lag in performance. Herein, the additive engineering of MA‐free organic−inorganic lead halide perovskites using divalent cations Sr2+ and Ca2+to enhance the performances of CsxFA1−xPbI3 perovskite compositions is explored. It is revealed that the addition of up to 0.5% of Sr2+ and Ca2+ leads to improvements in morphology and reduction in microstrain. The structural improvements observed correlate with improved solar cell performances at low additive concentrations.

Inorganic lead halide perovskites have a reasonable energy bandgap, which makes them ideal for tandem devices. As a result, inorganic lead halide perovskite solar cells (PSCs) could be prospective next-generation solar materials, but the issue of instability under moisture remains unaddressed. Adding 4-fluoro-phenyl-ethylammonium iodide (F-PEAI) spacer cations to the perovskite precursor solution is an elementary addition method to improve the performance of PSCs. We study the impact of F-PEAI on the perovskite crystal phase and the effect of F-PEAI concentration on PSC performance. F-PEAI was used to passivate interfacial flaws and vacancies in inverted inorganic PSCs and improve moisture tolerance, resulting in a mixed 2D/3D heterostructure. A small number of F-PEAI-treated PSCs have changed interfacial characteristics, resulting in better charge extraction and less charge recombination. The power conversion efficiency (PCE) of the F-PEAI treated device is much higher than that of the control group, and the PCE is improved to more than 11%. To attain high efficiency, all-inorganic perovskites can be modified using a straightforward method.

In article number 1605290, Hao-Wu Lin and co-workers report efficient all-vacuum-deposited inorganic cesium lead halide perovskite solar cells of which the stoichiometric ratios of the precursors were carefully calibrated by ellipsometry. The incorporation of bromine was exploited to further enhance the device performance and stability. The results provide a paragon for the use of inorganic precursors en route to efficient vacuum-deposited perovskite devices.

Though the cesium‐based inorganic perovskite solar cells (IPSCs) have developed rapidly in recent two years, the power conversion efficiency (PCE) is still far away from the Shockley–Queisser limit due to the large open‐circuit voltage (Voc) deficit, which results from the large energy loss (Eloss). Large Eloss has been a major obstacle for further efficiency improvement of IPSCs. In this review, the authors, for the first time, focus on investigating the Eloss of IPSCs and start from discussing the essence and origin of the Eloss. Then, the reported efficient methods for reducing the band tails and energy disorder are systematically summarized and reviewed, including crystallization optimization, defect passivation, and interface engineering. Finally, the authors offer an overall perspective on managing Eloss in IPSCs and point out the possible ways to reduce the Eloss and promote the efficiency. This review provides a basic understanding of Eloss and may inspire new designs or more impactful methods for further minimizing the Eloss of IPSCs.

Inorganic lead halide perovskites are attracting increasing attention due to their much better thermal stability than the organic–inorganic hybrid perovskite materials. Thus, the low power conversion efficiency (PCE) is a key issue for the inorganic lead halide perovskite solar cells (PSCs). This is mainly due to their wider bandgap and larger energy loss (Eloss) in the devices. Herein, for solving this issue, a dye molecule‐assisted engineering using the dye of 5,15‐bis(2,6‐dioctoxyphenyl)‐10‐(bis(4‐hexylphenyl)‐amino‐20‐4‐carboxyphenylethynyl)porphyrinato]zinc(II) (YD2‐o‐C8) is demonstrated. Results indicate that this molecule has a bifunctional effect, not only as a co‐sensitization layer for CsPbIBr2 with broader absorption spectrum but also reduces the Eloss by interface passivation. Specifically, the light absorption range of the photoactive layer is broadened from 600 to nearly 680 nm. At the same time, the interfacial charge recombination is highly reduced. After optimizing, the champion PCE is enhanced from 7.02% to 10.13%, and record‐high open‐circuit voltage (VOC) of 1.37 V and short‐circuit currents (JSC) of 12.05 mA cm−2 are achieved. This study opens a simple and efficient way to improve the efficiency of inorganic PSCs.

Inorganic lead-based halide perovskites: From fundamental properties to photovoltaic applications

The solution-processed organic–inorganic lead halide perovskite solar cells have recently emerged as promising candidates for the conversion of solar power into electricity.

In this paper we address the JV hysteresis behavior of planar organic–inorganic lead halide perovskite solar cells fabricated using PC60BM as the cathode. At room temperature, these devices exhibit apparently hysteresis free JV scans. We observe that cooling the temperature to 175 K results in the appearance of substantial JV hysteresis. Employing chronoamperometric measurements, we demonstrate that the half-time for the relaxation process underlying this hysteresis slows from 0.6 s at 298 K to 15.5 s at 175 K, yielding an activation energy of 0.12 eV. We further demonstrate that by cooling a cell to 77 K while held under positive bias, we are able to “freeze” the cell into the most favorable condition for efficient photovoltaic performance. We thus conclude that changes to device architecture that appear to remove room temperature JV hysteresis may not remove the underlying process(es), but rather shift them to time scales not readily observable in typical room temperature JV scans.

New photovoltaic materials have been extensively searched for in the last decade for clean and renewable solar energy conversion. Among them, the organic–inorganic hybrid lead halide perovskite solar cell is of current interest to the solar cell community because of its low processing cost, ease of fabrication and high power conversion efficiency. These perovskites show great potential to be photovoltaic absorbers with excellent optoelectronic properties, for example, high absorption coefficient, long charge carrier diffusion length, moderate ambipolar mobilities, tunable bandgap, etc. The unique physical and chemical properties of these materials are based on the crystal structure of the perovskites, named after the mineral form of CaTiO3. Most inorganic materials with a perovskite crystal structure typically show ferroelectric properties. Ferroelectricity in methylammonium lead tri-iodide (MAPbI3), an absorbing material in perovskite solar cells with a perovskite crystal structure, is now a topic of debate. Some theoretical and experimental investigations have shown the presence of a ferroelectric domain in these perovskites, although a lot of controversial results and conclusions also exist in the literature. In this review, notable signs of progress in the theoretical and experimental studies regarding ferroelectricity in organic-inorganic hybrid perovskites are summarized. In addition, future improvements of ferroelectric perovskites are proposed, paving the way towards prospective high-performance flexible and wearable ferroelectric solar cells and optoelectronic devices.

Organic–inorganic lead halide perovskites solar cells (PSCs) show great potential in the photovoltaic system, reaching overall power conversion efficiencies (PCE) up to 25.2%. The rapid increase of PCE in PSCs has made them the rising star of the photovoltaics world, with great interest to the academic community. Long‐term stability under working environments remains a significant challenge for the commercialization of PSCs, particularly those using inorganic–organic halide lead perovskite absorbers. In this regard, only the devices that can maintain long‐term stability under conditions of temperature, humidity, and UV irradiation can be called stable solar cells. This Review highlights the sources for the chemical instability problems in conventional CH3NH3PbI3‐based perovskite solar cells from humidity instability, phase instability, thermal instability, and ion migration. In pursuit of highly stable PSCs, this article also discusses the strategies to stabilize PSCs through both external and internal aspects without sacrificing the PCE, specifically including additive engineering with surface passivation and composition engineering.

Organic-inorganic lead halide perovskite solar cells (PSCs) are highly efficient, flexible, lightweight, and even tolerant to radiation, such as protons, electron beams (EB), and γ-rays, all of which makes them plausible candidates for use in space satellites and spacecrafts. However, the mechanisms of radiation damage of each component of PSC [an organic hole transport material (HTM), a perovskite layer, and an electron transport material (ETM)] are not yet fully understood. Herein, we investigated the EB irradiation effect (100 keV, up to 2.5 × 1015 cm-2) on binary-mixed A site cations and halide perovskite (MA0.13FA0.87PbI2.61Br0.39, MA:methylammonium cation and FA:formaminidium cation), a molecular HTM of doped SpiroOMeTAD, and an inorganic ETM of mesoporous TiO2. Despite the decreased power conversion efficiency of PSCs upon EB exposure, the photoconductivities of the perovskite, HTM, and ETM layers remained intact. In contrast, significant dedoping of HTM was observed, as confirmed by steady-state conductivity, photoabsorption, and X-ray photoelectron spectroscopy measurements. Notably, this damage could be healed by exposure to short-wavelength light, leading to a partial recovery of the PSC efficiency. Our work exemplifies the robustness of perovskite against EB and the degradation mechanism of the overall PSC performance.

Under the groundswell of calls for the industrialization of perovskite solar cells (PSCs), wide‐bandgap (>1.7 eV) mixed halide perovskites are equally or more appealing in comparison with typical bandgap perovskites when the former's various potential applications are taken into account. In this review, the progress of wide‐bandgap organic–inorganic hybrid PSCs—concentrating on the compositional space, optimization strategies, and device performance—are summarized and the issues of phase segregation and voltage loss are assessed. Then, the diverse applications of wide‐bandgap PSCs in semitransparent devices, indoor photovoltaics, and various multijunction tandem devices are discussed and their challenges and perspectives are evaluated. Finally, the authors conclude with an outlook for the future development of wide‐bandgap PSCs.

The power conversion efficiency (PCE) of organic–inorganic lead halide perovskite solar cells (PSCs) has exceeded 25%, approaching the best record of their silicon counterpart. However, lifetime issues still stand between PSCs and the goal of mass commercialization. For instance, most photoactive perovskites are hydrophilic, and moisture can quickly turn some of their constituents to compounds yielding trap states. Some perovskites are not thermally stable in the temperature window of solar cell operation and will transform into photo-inactive non-perovskites. If a perovskite is of an inadequate quality, e.g., vacancies, surface area, or grain boundaries per unit volume are high, there exist more defect sites, acting as migration pathways for perovskite ions under photo-bias, and the migration changes the perovskite's composition. An unstable perovskite/charge transport material (CTM) interface allows cross-contamination between molecules from both sides of the interface. Even without external stress, perovskite ions in an operating PSC undergo redox processes, which create defect states or initiate chemical chain reactions to accelerate PSC degradation. This mini-review discussed recent progress in solving issues, including the above, to stabilize PSCs with competitive PCE beyond 20%. The remarkable longevity of 15 PSCs under accelerated aging tests was probed in depth from three viewpoints: (1) perovskite compositions and dopants, (2) perovskite additives, and (3) CTMs. This mini-review, within which crucial perovskite-stabilizing methods were systematically analyzed, can be used as a quick-start guide when dealing with PSCs' stability in the future.