xiaodaibudai

An analytical solution of photoluminescence reabsorption (PLr) is used to determine the intrinsic radiative carrier recombination rate of metal-halide perovskite films. Simulation of its impact on the quasi-Fermi-level splitting (QFSL) reveals it is detrimental at high, but advantageous at low nonradiative recombination rates. Importantly, neglecting PLr results in overestimation of the effective nonradiative recombination rate in perovskite solar cells.

The precise quantification of the impact of photoluminescence reabsorption (PLr) in metal-halide perovskite solar cells (PSCs) remains challenging. Herein, the PLr effect is examined by combined time-resolved photoluminescence (TRPL) spectroscopy and time-resolved terahertz spectroscopy (TRTS) and a model is proposed that relates both, the PLr and nonradiative recombination rate (k _nr) to the quasi-Fermi-level splitting (QFLS). PLr is shown to be beneficial for QFLS when the nonradiative recombination rate (k _nr) is below a critical value of ≈7 × 10⁵ s⁻¹; at high k _nr PLr is detrimental to QFLS. By incorporating PLr into a two-diode model that allows extraction of the effective k _nr, the series resistance (r _s), and the shunt resistance (r _sh) in PSCs, it is found that neglecting PLr overestimates the effective k _nr, although it does not affect the value of r _s and r _sh. The findings herein provide insight into the impact of the PLr effect on metal-halide PSCs.

Dual passivation strategy for high efficiency inorganic CsPbI₂Br solar cells is demonstrated. A synergetic effect from the dual passivation of the trap defects in the CsPbI₂Br film by KBr and phenethylammonium chloride (PEACl) is demonstrated, which is beneficial to the better growth of the CsPbI₂Br film with reduced trap defects, enlarged grain size, and formation of an ultrathin low-dimensional perovskite surface layer.

Inorganic metal halide perovskite solar cells have achieved incredible progress in recent years. However, the power conversion efficiency of the inorganic perovskite solar cells is still low compared with their hybrid counterparts due to the inescapable nonradiative losses from the charge recombination. Herein, a strategy is demonstrated to minimize the nonradiative recombination loss in CsPbI₂Br solar cells by establishing a synergetic passivation from the mutual effect of alkali- and alkylammonium-salt. Accordingly, a sequential passivation process employing KBr and phenethylammonium chloride overcomes their limited passivation effect in one single step. This dual passivation is beneficial to an improved CsPbI₂Br film with reduced trap defects, enlarged grain size, as well as to form an ultrathin low-dimensional perovskite surface layer. As a result, a very high power conversion efficiency of 16.9% is obtained for inorganic CsPbI₂Br solar cells. The proposed dual passivation scheme provides a feasible route not only for the design of high-efficiency perovskite solar cells but also for other perovskite-related optoelectronic devices.

Gradient 1D/3D perovskite bilayer using 4-tert-butylpyridinium cation (TBP⁺) as a cation for 1D perovskite layer is introduced. The crystal structure and fundamental properties of 1D perovskite (TBPPbI₃) are investigated. Gradient 1D/3D perovskite-based devices show an improved power conversion efficiency from 18.3% to 19.3% due to the enhanced hole extraction process and suppressed carrier recombination.

To achieve both high efficiency and long-term stability of perovskite solar cells (PSCs), it is effective to use a perovskite layer in which a low-dimensional perovskite layer is stacked on a 3D perovskite layer. However, the guidelines for the effective structure of these perovskite layers remain unclear. Herein, the gradient structured 1D perovskite layer formed on top of a 3D perovskite layer using 4-tert-butylpyridinium iodide (TBPI) as a capping layer is introduced. It is demonstrated that the gradient structured 1D perovskite layer on the 3D perovskite improves the conversion efficiency of PSCs despite the lateral orientation of the (PbI₃ ⁻) _n linear chain of the 1D perovskite, which is responsible for electronic conduction. In addition, it is found that the hydrophobic organic unit of TBPI protects the 3D perovskite layer, which enhances its long-term stability.

The full-scale mixed cation-doped FA _x Cs_1−x PbI₃ perovskites are synthesized and studied. The FA_0.6Cs_0.4PbI₃ perovskite solar cells exhibit more stable efficiency, the champion device reaches a power conversion efficiency of 20.40%. Meanwhile, the unencapsulated devices keep 90% of the initial efficiency when stored in air for 30 days.

FA _x Cs_1−x PbI₃ perovskites were considered promising candidates to accomplish the goals of high photoelectric conversion efficiency with great stability. Limited by the phase separation during fabrication through the conventional one-step method, the FA _x Cs_1−x PbI₃ perovskites with the x ratio lower than 0.7 were barely studied. Herein, the full-scale mixed cation-doped FA _x Cs_1−x PbI₃ perovskites are synthesized and studied. The bandgap of FA _x Cs_1−x PbI₃ perovskites gradually decreases from 1.69 to 1.58 eV with x increasing from 0.15 to 0.75, along with phase structure changes from tetragonal (β) to cubic (α). Under humidity or UV irradiation, the FA _x Cs_1−x PbI₃ perovskites phase separates to FA_0.92Cs_0.08PbI₃ perovskite and δ-CsPbI₃. The FA_0.60Cs_0.40PbI₃ perovskite solar cells exhibit more stable efficiency, the champion device reaches a power conversion efficiency of 20.40%. Meanwhile, the unencapsulated devices keep 90% of the initial efficiency when stored in air for 30 days, showing the potential for high stability photovoltaic devices.

The interface passivation and performance enhancements of perovskite solar cell (PSCs) devices are realized by introducing few-layer nonmetallic element sulfur-doped graphite carbon nitride nanosheets in the SnO₂-based electron transport layer (ETL) at the first time, which is attributed to the enhanced electron mobility and conductivity of CNS-modified ETL, reduced interfacial trap state density, and improved crystallinity of perovskite film.

High-quality electron transport layer (ETL) is beneficial to improve the charge extraction and transport, which determines the performance of perovskite solar cells (PSCs). However, the unbalanced charge extraction and interface problems commonly occur in the tin oxide (SnO₂) ETL. Herein, the sulfur-doped graphite carbon nitride (CNS) nanosheets are prepared and utilized for modifying the SnO₂ ETL to fabricate high-performance PSCs. The CNS-modified SnO₂ ETL exhibits enhanced electron mobility and conductivity, and matched energy level with perovskite, which promotes the extraction and transport of charge carriers at the interface, and balances charge extraction with the hole transport layer. In addition, interfacial carrier recombination is significantly reduced through effective interface passivation of sulfur atoms in CNS with the undercoordinated lead ions in perovskite films. Meanwhile, the introduction of an interfacial control material CNS also contributes to improve the crystalline quality of perovskite films with increasing grain size and light absorption intensity. As a consequence, an outstanding improvement in power conversion efficiency (PCE) from 18.98% to 20.33% is achieved after introducing CNS into the SnO₂ ETL, as well as an enhancement in stability against humidity, retaining near 90% of the initial PCE after aging in the ambient atmosphere for 30 days.

Mixing chlorobenzene (CB) and H₂O in the perovskite precursor is an effective method to improve the direct contact between poly-TPD and the perovskite active layer. Inverted (p–i–n) perovskite solar cells based on the modified perovskite display efficient hole-interface charge transfer and suppression of the bulk and interfacial nonradiative recombination, thereby achieving an excellent power conversion efficiency of 22.1%.

Inverted perovskite solar cells (IPSCs) suffer from perishing interface contact due to the non-wetting hole-transport layer (HTL). Herein, the several classes of solvent to the perovskite precursor (the process is defined as solvent-additive engineering) for achieving an improvement in the interface contact between nonwetting HTL and active perovskite layer, suitably achieving improved hole-interface charge transfer, are mixed. Also, a high-quality perovskite layer with high crystallinity, large grain distribution, and flat surface morphology is obtained based on solvent-additive engineering, which affords a lower bulk and interface trap density. IPSCs with the modified perovskite layer show suppression of nonradiative recombination on the surface and in the bulk of the perovskite, thereby achieving an outstanding power conversion efficiency of 20.6%. In addition, IPSCs using a mixed-cation perovskite (FA_0.83Cs_0.07MA_0.13PbI_2.64Br_0.39) are also fabricated and a highest efficiency of 22.1%, visualizing the broad applicability of this method, is achieved. This simple, low-cost, and efficient solvent-additive strategy can solve interface contact problems and improve perovskite quality, thus potentially giving rise to other applications.

A low-dimensional perovskite layer is constructed between the perovskite absorber and carbon electrode in printable triple-mesoscopic perovskite solar cells by posttreatment. By forming graded type-II band alignment, the device performance is significantly enhanced, delivering a power conversion efficiency of 17.47% with an open-circuit voltage of 1.02 V.

Abstract

Printable hole-conductor-free perovskite solar cells (PSCs) have attracted intensive research attention due to their high stability and simple manufacturing process. However, the cells have suffered severe potential loss in the absence of the hole transporting layer. The dimensionality of the perovskite absorber in the mesoporous carbon electrodes by conducting post-treatments is reduced. The low-dimensional perovskites possess wide-bandgaps and form type-II band alignment, favoring directional charge transportation and thus enhancing the device performance. For the cells using MAPbI₃ (MA = methylammonium) as the light absorber, the open-circuit voltage (V _OC) is significantly enhanced from 0.92 to 0.98 V after posttreatment, delivering an overall efficiency of 16.24%. For the cells based on FAPbI₃ (FA = formamadinium), a high efficiency of 17.47% is achieved with V _OC of 1.02 V, which are both the highest reported values for printable hole-conductor-free PSCs. This strategy provides a facile method for tuning the energy level alignment for mesoscopic perovskite-based optoelectronics.

The work presents a detailed understanding of solution-processing-dependent quantum well growth and its impact on charge transport and photovoltaic performance for Dion–Jacobson perovskite. Faster solvent removal during film formation leads to a gradient distribution of the quantum wells and a preferential perpendicular orientation. The highest efficiency of 15.81% for aromatic spacer-based Dion–Jacobson perovskite solar cells is achieved.

Abstract

Dion–Jacobson (DJ) 2D hybrid perovskite semiconductors offer improved environmental stability and higher structural diversity in comparison with their 3D analogous. However, lacking of controlled perovskite crystallization makes it a challenge to achieve high charge transport for photovoltaic devices. Here, a detailed understanding of effects on film formation during different solution-casting processes for the DJ perovskite (PDMA)(MA) _{n −1}Pb _n I_{3 n +1} (<n> = 4, PDMA refers to 1,4-phenylenedimethanammonium) in the final film structure and photovoltaic outcomes is presented. Faster removal of solvent from solution via hot-casting or antisolvent dripping results in a more uniform thickness distribution of quantum wells. This eventually enhances carrier transport greatly along perpendicular direction and increases power conversion efficiencies. A high efficiency of 15.81% is achieved for the hot-casting devices, which is also the highest for aromatic spacer-based DJ perovskite solar cells. This work helps to better understand the control of film formation during solution-casting for high performance solar cells.

A mesoporous charge-transporting layer is embedded into quasi-interdigitated back-contact perovskite devices. The increased interfacial contact area significantly enhances the charge extraction behavior leading to a record high current density of 21.3 mA cm⁻² on a back-contact perovskite device.

Abstract

As the performance of organic–inorganic halide perovskite solar cells approaches their practical limits, the use of back-contact architectures, which eliminate parasitic light absorption, provides an effective route toward higher device efficiencies. However, a poor understanding of the underlying device physics has limited further performance improvements. Here a mesoporous charge-transporting layer is introduced into quasi-interdigitated back-contact perovskite devices and the charge extraction behavior with an increased interfacial contact area is studied. The results show that the incorporation of a thin mesoporous titanium dioxide layer significantly shortens the charge-transfer lifetime and results in more efficient and balanced charge extraction dynamics. A high short-circuit current density of 21.3 mA cm^–2 is achieved using a polycrystalline perovskite layer on a mesoscopic quasi-interdigitated back-contact electrode, a record for this type of device architecture.

This review aims to discuss challenges and recent advances in all-inorganic perovskites for advanced photovoltaics. After discussing the structural and electronic properties of the materials, the focus of this review moves towards all-inorganic perovskite solar cells, reporting the most effective approaches to improve device performance. Finally, efforts and challenges toward the fabrication of all-inorganic perovskite solar modules are discussed.

Abstract

In the last ten years, organic–inorganic hybrid perovskites have been skyrocketing the field of innovative photovoltaics (PVs) and now represent one of the most promising solution for next-generation PVs. Within the family of halide perovskites, increasing attention has been focused on the so-called all-inorganic group, where the organic cation is replaced by cesium, as in the case of CsPbI₃. This subclass of halide perovskites features desirable optoelectronic properties such as easily tunable bandgap, strong defect tolerance, and improved thermal stability compared to the hybrid systems. When integrated in PV cells, they exhibit high power conversion efficiency (PCE) with record values of 19.03%. However, all-inorganic perovskite solar cells (PCSs) face several challenges such as i) instability of the CsPbI₃ photoactive phase in ambient conditions, ii) inhomogeneous film morphology, and iii) high surface defect density. This work focuses on the mentioned challenges with a special attention on discussing the Cs–Pb–X system (X = I, Br). Then, the most recent and effective approaches for increasing both the PCE and the stability of devices are reviewed, which include material doping, interface engineering, and device optimization. Finally, the first efforts toward the upscaling of Cs-based PSCs, and predicted methods for enabling large-scale production, are discussed.

This work presents a comprehensive review on the current understanding, and apparent contradictions, of experimental observation, interpretation, and theoretical hypotheses presented in the state-of-the-art mixed dimensional 2D-3D perovskite literature and identifies promising future research directions for enhancing the stability and performance of such devices.

Abstract

Perovskite solar cells are a potential game changer for the photovoltaics industry, courtesy of their facile fabrication and high efficiency. Despite this, commercialization is being held back by poor stability. To become economically feasible for commercial production, perovskite solar cells must meet or exceed industry standards for operational lifetime and reliability. In this regard, mixed dimensional 2D-3D perovskite solar cells, incorporating long carbon-chain organic spacer cations, have shown promising results, with enhancement in both device efficiency and stability. Dimensional engineering of perovskite films requires a delicate balance of 2D and 3D perovskite composition to take advantage of the specific properties of each material phase. This review summarizes and assesses the current understanding, and apparent contradictions in the state-of-the-art mixed dimensional perovskite solar cell literature regarding the origin of stability and performance enhancement. By combining and comparing results from experimental and theoretical studies it is focused on how the perovskite composition, film formation methods, additive and solvent engineering influence efficiency and stability, and identify future research directions to further improve both key performance metrics.

Light soaking (LS) is found to activate halide ion migration and significantly passivate the defects. By adding excessive PbI₂ in the precursor, the LS effect can be controlled and suppressed. An efficiency of 18.14% is achieved in all-inorganic CsPb(I_0.8Br_0.2)₃ perovskite solar cells with reduced LS time.

Abstract

Light soaking (LS) has been reported to positively influence the device performance of perovskite solar cells (PSCs), which, however, could be potentially harmful to the loaded devices due to the unstable output. There are very few reports on controls over the LS effect, especially in all-inorganic PSCs. In this study, a remarkable LS induced performance enhancement of CsPb(I_{1− x} Br _x )₃ based PSCs is presented. In situ grazing-incidence wide-angle X-ray scattering measurements quantize the temperature increase under illumination and reveal a radiative heating-induced lattice expansion. The device curing time is shortened with the increased Br/I ratio, evidently correlated with their distinct mobility and activation energy. It is suggested that LS could promote the migration of halide ions, giving rise to notable defect passivation and thus device improvements. Based on these understandings, an effective means is proposed to suppress the LS effect, which is to incorporate slightly over-stochiometric PbI₂ in precursor, and a champion PCE of 18.14% in all-inorganic PSCs with significantly reduced device curing time is obtained.

A novel strategy is developed for preparing high-efficient perovskite solar cells (PSCs) with ferroelectricity by incorporating 1D ferroelectric perovskite with 3D organic–inorganic hybrid perovskite (OIHP). The 1D/3D mixed OIHP films exhibit evident ferroelectricity, and the 1D perovskite is randomly distributed. The poling of the 1D/3D mixed PSCs increase V _oc, and the ferroelectric-polarization is retained for a long time.

Abstract

With the capability to manipulate the built-in field in solar cells, ferroelectricity is found to be a promising attribute for harvesting solar energy in solar cell devices by influencing associated device parameters. Researchers have devoted themselves to the exploration of ferroelectric materials that simultaneously possess strong light absorption and good electric transport properties for a long time. Here, it is presented a novel and facile approach of combining state-of-art light absorption and electric transport properties with ferroelectricity by the incorporation of room temperature 1D ferroelectric perovskite with 3D organic–inorganic hybrid perovskite (OIHP). The 1D/3D mixed OIHP films are found to exhibit evident ferroelectric properties. It is notable that the poling of the 1D/3D mixed ferroelectric OIHP solar cell can increase the average V _oc can be increased from 1.13 to 1.16 V, the average PCE from 20.7% to 21.5%. A maximum power conversion efficiency of 22.7%, along with an enhanced fill factor of over 80% and open-circuit voltage of 1.19 V, can be achieved in the champion device. The enhancement is by virtue of reduced surface recombination by ferroelectricity-induced modification of the built-in field. The maximum power point tracking measurement substantiates the retention of ferroelectric-polarization during the continued operation.

A ligand molecule containing carbonyls (carboxyl and amide) and a long hydrophobic alkyl chain is incorporated into a perovskite precursor to achieving improved crystallinity, reduced trap state density, and inhibited ion migration. This strategy enables an impressive power conversion efficiency exceeding 23% with inhibited hysteresis.

Abstract

The nonradiative recombination losses resulting from the trap states at the surface and grain boundaries directly hinder the further enhancement of power conversion efficiency (PCE) and stability of perovskite solar cells. Consequently, it is highly desirable to suppress nonradiative recombination through modulating perovskite crystallization and passivating the defects of perovskite films. Here, a simple and effective multifunctional additive engineering strategy is reported where 11 Maleimidoundecanoic acid (11MA) units with carbonyls (carboxyl and amide) and long hydrophobic alkyl chain are incorporated into a perovskite precursor solution. It is revealed that improved crystallinity, reduced trap state density, and inhibited ion migration are achieved, which is ascribed to the strong coordination interaction between the carbonyl groups at both sides of 11MA molecules and Pb²⁺. As a result, improved efficiency and stability are achieved simultaneously after introducing 11MA additive. The device with 11MA additive delivers a champion PCE of 23.34% with negligible hysteresis, which is significantly higher than the 18.24% of the control device. The modified device maintains around 91% of its initial PCE after aging under ambient conditions for 3000 h. This work provides a guide for developing multifunctional additive molecules for the purpose of simultaneous improvement of efficiency and stability.

An electrospray printing technique is developed to continuously print the TiO₂ electron transport layer, perovskite layer, and carbon layer, enabling a cost‐effective device. The electrospray technique is capable of printing uniform, compact, and high adhesion layers with controllable dimensions and patterns. This work demonstrates a fully printed low‐cost solar cell and provides a feasible process for perovskite solar cells to initial industrialization.

Abstract

With the power conversion efficiencies of perovskite solar cells (PSCs) exceeding 25%, the PSCs are a step closer to initial industrialization. Prior to transferring from laboratory fabrication to industrial manufacturing, issues such as scalability, material cost, and production line compatibility that significantly impact the manufacturing remain to be addressed. Here, breakthroughs on all these fronts are reported. Carbon‐based PSCs with architecture fluorine doped tin oxide (FTO)/electron transport layer/perovskite/carbon, that eliminate the need for the hole transport layer and noble metal electrode, provide ultralow‐cost configuration. This PSC architecture is manufactured using a scalable and industrially compatible electrospray (ES) technique, which enables continuous printing of all the cell layers. The ES deposited electron transport layer and perovskite layer exhibit properties comparable to that of the laboratory‐scale spin coating method. The ES deposited carbon electrode layer exhibits superior conductivity and interfacial microstructure in comparison to films synthesized using the conventional doctor blading technique. As a result, the fully ES printed carbon‐based PSCs show a record 14.41% power conversion efficiency, rivaling the state‐of‐the‐art hole transporter‐free PSCs. These results will immediately have an impact on the scalable production of PSCs.

Aided by theoretical calculation, a multifunctional 2,2‐difluoropropanediamide (DFPDA) molecule that bears carbonyl, amino, and fluorine groups is first introduced into the perovskite precursor, serving as a crystal growth mitigator, grain boundaries passivator, and surface protection material. With the help of the combined effects of multifunctional groups in DFPDA, the perovskite cells deliver an efficiency of 22.21% and improved stability.

Abstract

With a certified efficiency as high as 25.2%, perovskite has taken the crown as the highest efficiency thin film solar cell material. Unfortunately, serious instability issues must be resolved before perovskite solar cells (PSCs) are commercialized. Aided by theoretical calculation, an appropriate multifunctional molecule, 2,2‐difluoropropanediamide (DFPDA), is selected to ameliorate all the instability issues. Specifically, the carbonyl groups in DFPDA form chemical bonds with Pb²⁺ and passivate under‐coordinated Pb²⁺ defects. Consequently, the perovskite crystallization rate is reduced and high‐quality films are produced with fewer defects. The amino groups not only bind with iodide to suppress ion migration but also increase the electron density on the carbonyl groups to further enhance their passivation effect. Furthermore, the fluorine groups in DFPDA form both an effective barrier on the perovskite to improve its moisture stability and a bridge between the perovskite and HTL for effective charge transport. In addition, they show an effective doping effect in the HTL to improve its carrier mobility. With the help of the combined effects of these groups in DFPDA, the PSCs with DFPDA additive achieve a champion efficiency of 22.21% and a substantially improved stability against moisture, heat, and light.

An in‐situ formed polymeric interlayer enables enhanced photovoltaic performance of the methylammonium‐, cesium‐, and bromide‐free perovskite solar cells with superior photo‐ and thermal‐stability. The polymeric interlayer promotes growth of perovskite crystals with reduced defect density and improves the contact between the perovskite and hole transporting layers to assists in photo‐excited charge extraction.

Abstract

The vast majority of high‐performance perovskite solar cells (PSCs) are based on multi‐cation mixed‐anion compositions incorporating methylammonium (MA) and bromide (Br). Nevertheless, the thermal instability of MA and the tendency of mixed halide compositions to phase segregate limit the long‐term stability of PSCs. However, reports of MA‐free and/or Br‐free compositions are rare in the community since their performance is generally inferior. Here, a strategy is presented to achieve highly efficient and stable PSCs that are altogether cesium (Cs)‐free, MA‐free and Br‐free. An antisolvent quenching process is used to in‐situ deposit a polymeric interlayer to promote the growth of phase‐pure formamidinium lead tri‐iodide perovskite crystals with reduced defect density and to assist in photo‐excited charge extraction. The PSCs developed are among the best‐performing reported for such compositions. Moreover, the PSCs show superior stability under continuous exposure to both illumination and 85 °C heat.

Herein, novel Ruddlesden–Popper Cs₂PbI₂Cl₂ nanosheets are synthesized and creatively employed as a multifunctional interface optimization material to improve the performance of CsPbI₂Br solar cells. Based on the heterostructured NSs/CsPbI₂Br/NSs inorganic film, an efficiency of 16.65% is obtained, which is one of the best reported for CsPbI₂Br solar cells, along with much‐enhanced UV, air, and thermal stabilities.

Abstract

Inorganic CsPbI₂Br perovskite solar cells (PSCs) have gained enormous research interest due to their excellent thermal and light stabilities. However, their unsatisfactory power‐conversion efficiency and poor intrinsic phase stability remain roadblocks to their further development. Herein, Cs₂PbI₂Cl₂ nanosheets (NSs) with the Ruddlesden–Popper (RP) structure are synthesized, and an NSs/CsPbI₂Br/NSs heterostructure is employed to enhance both the stability and efficiency of CsPbI₂Br solar cells. The novel Cs₂PbI₂Cl₂ NSs can not only passivate the top and bottom surfaces of the perovskite film and top surface of the TiO₂ film but also enhance the stability of the perovskite film. Based on the heterostructured NSs/CsPbI₂Br/NSs inorganic perovskite film, the efficiency of the CsPbI₂Br PSCs is improved from 15.02% to 16.65%. Moreover, the unencapsulated CsPbI₂Br devices with the NSs/CsPbI₂Br/NSs heterostructure sustain over 90% of their original efficiencies after being exposed to ambient conditions (≈25 °C and ≈35% RH) for 648 h. Both the UV‐light‐soaking stability (100 mW cm⁻¹ 365 nm UV light) and thermal stability (T = 85 °C) of the optimized devices are dramatically improved in comparison with their counterparts with only a 3D active layer. Therefore, this work promotes the application of RP inorganic perovskite nanocrystals in a range of perovskite optoelectronic devices.

Novel interface polarization induced field‐effect passivation based on amorphous transition metal oxide is developed for efficient and ambient‐air‐stable perovskite solar cells. Comprehensive insights into the interaction between the field‐effect passivation, interface polarities, and the performance of the device have been elucidated in detail.

Abstract

Organolead halide hybrid perovskite solar cells (PSCs) have become a shining star in the renewable devices field due to the sharp growth of power conversion efficiency; however, interfacial recombination and carrier‐extraction losses at heterointerfaces between the perovskite active layer and the carrier transport layers remain the two main obstacles to further improve the power conversion efficiency. Here, novel field‐effect passivation has been successfully induced to effectively suppress the interfacial recombination and improve interfacial charge transfer by incorporating interfacial polarization via inserting a high work function interlayer between perovskite and holes transport layer. The charge dynamics within the device and the mechanism of the field‐effect passivation are elucidated in detail. The unique interfacial dipoles reinforce the built‐in field and prevent the photogenerated charges from recombining, resulting in power conversion efficiency up to 21.7% with negligible hysteresis. Furthermore, the hydrophobic interlayer also suppresses the perovskite decomposition by preventing the moisture penetration, thereby improving the humidity stability of the PSCs (>91% of the initial power conversion efficiency (PCE) after 30 d in 65 ± 5% humidity). Finally, several promising research perspectives based on field‐effect passivation are also suggested for further conversion efficiency improvements and photovoltaic applications.

An anion/cation synergy strategy is proposed by the incorporation of ZnI₂ in CsPbI₃ quantum dots (QDs) to improve the stability and photoelectric properties. The obtained Zn:CsPbI₃ QDs show lower defect state density and enhanced structural stability. Perovskite quantum dot solar cells fabricated with Zn:CsPbI₃ QDs exhibit a champion power conversion efficiency over 16%.

Abstract

All‐inorganic CsPbI₃ quantum dots (QDs) have shown great potential in photovoltaic applications. However, their performance has been limited by defects and phase stability. Herein, an anion/cation synergy strategy to improve the structural stability of CsPbI₃ QDs and reduce the pivotal iodine vacancy (V _I) defect states is proposed. The Zn‐doped CsPbI₃ (Zn:CsPbI₃) QDs have been successfully synthesized employing ZnI₂ as the dopant to provide Zn²⁺ and extra I⁻. Theoretical calculations and experimental results demonstrate that the Zn:CsPbI₃ QDs show better thermodynamic stability and higher photoluminescence quantum yield (PLQY) compared to the pristine CsPbI₃ QDs. The doping of Zn in CsPbI₃ QDs increases the formation energy and Goldschmidt tolerance factor, thereby improving the thermodynamic stability. The additional I⁻ helps to reduce the V _I defects during the synthesis of CsPbI₃ QDs, resulting in the higher PLQY. More importantly, the synergistic effect of Zn²⁺ and I⁻ in CsPbI₃ QDs can prevent the iodine loss during the fabrication of CsPbI₃ QD film, inhibiting the formation of new V _I defect states in the construction of solar cells. Consequently, the anion/cation synergy strategy affords the CsPbI₃ quantum dot solar cells (QDSC) a power conversion efficiency over 16%, which is among the best efficiencies for perovskite QDSCs.

A biological polymer is employed to regulate the arrangement of SnO₂ nanocrystals on a substrate and induce vertical crystal growth of a perovskite layer on top. The enhanced interface contact between the electron‐transport layer and the perovskite layer significantly contributes to the improvement of efficiency and stability of derived planar perovskite solar cells.

Abstract

Perovskite solar cells (PSCs) have rapidly developed and achieved power conversion efficiencies of over 20% with diverse technical routes. Particularly, planar‐structured PSCs can be fabricated with low‐temperature (≤150 °C) solution‐based processes, which is energy efficient and compatible with flexible substrates. Here, the efficiency and stability of planar PSCs are enhanced by improving the interface contact between the SnO₂ electron‐transport layer (ETL) and the perovskite layer. A biological polymer (heparin potassium, HP) is introduced to regulate the arrangement of SnO₂ nanocrystals, and induce vertically aligned crystal growth of perovskites on top. Correspondingly, SnO₂–HP‐based devices can demonstrate an average efficiency of 23.03% on rigid substrates with enhanced open‐circuit voltage (V _OC) of 1.162 V and high reproducibility. Attributed to the strengthened interface binding, the devices obtain high operational stability, retaining 97% of their initial performance (power conversion efficiency, PCE > 22%) after 1000 h operation at their maximum power point under 1 sun illumination. Besides, the HP‐modified SnO₂ ETL exhibits promising potential for application in flexible and large‐area devices.

High-efficiency lead halide perovskite solar cells (PSCs) have been fabricated with α-phase formamidinium lead iodide (FAPbI₃) stabilized with multiple cations. The alloyed cations greatly affect the bandgap, carrier dynamics, and stability, as well as lattice strain that creates unwanted carrier trap sites. We substituted cesium (Cs) and methylenediammonium (MDA) cations in FA sites of FAPbI₃ and found that 0.03 mol fraction of both MDA and Cs cations lowered lattice strain, which increased carrier lifetime and reduced Urbach energy and defect concentration. The best-performing PSC exhibited power conversion efficiency >25% under 100 milliwatt per square centimeter AM 1.5G illumination (24.4% certified efficiency). Unencapsulated devices maintained >80% of their initial efficiency after 1300 hours in the dark at 85°C.