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Dion–Jacobson (DJ) and alternating-cation-interlayer (ACI) phases are two emerging types of layered 2D halide perovskites with high potential in balanced charge-transport properties and chemical stability. By tailoring the molecular, thin-film, and device chemistries, high-performance solar cells have been demonstrated.

Abstract

Layered halide perovskites (LHPs) with crystallographically 2D structures have gained increasing interest for photovoltaic applications due to their superior chemical stability and intriguing anisotropic properties, which are in contrast to their conventional 3D perovskite counterparts. The most frequently studied LHPs are Ruddlesden–Popper (RP) phases, which suffer from a carrier-transport bottleneck due to the van der Waals gap associated with their intrinsic organic interlayer structures. To address this issue, Dion–Jacobson (DJ) and alternating-cation-interlayer (ACI) LHPs have rapidly emerged, which exhibit unique structural and (opto)electronic characteristics that may resemble those of the 3D counterparts owing to the eliminated or reduced van der Waals gap. Improved photophysical properties have been achieved in DJ and ACI LHPs, leading towards better photovoltaic performance. Here we provide a comprehensive discussion on the merits and promises of DJ and ACI LHPs from a chemistry perspective. Then, we review recent progress on the synthesis and tailoring of DJ and ACI LHP crystals and thin films, as well as their optoelectronic properties and photovoltaic performance. Finally, we discuss possible pathways to overcome critical challenges to realize the full potential of DJ and ACI LHPs for high-performance solar cells and beyond.

By introducing a dipole layer at the indium tin oxide/perovskite interface of the electron transport layer-free devices, with an efficient quantum tunneling effect, a quasi-ohmic contact of the front interface is realized. As a result, the device changes from a metal-semiconductor/PN cascade heterojunction solar cell to a single PN junction solar cell, and the corresponding ideal factor is reduced from 3.35 to 2.05.

Abstract

The pursuit of high power conversion efficiency (PCE) and cost-effective perovskite solar cells (PSCs) has spawned many innovative device structure designs. Compared with the traditional NIP type PSCs, electron transport layer (ETL) free PSCs have attracted growing attention due to their enormous potential in large area, low-cost flexible application. However, there is still a lack of in-depth understanding of the energy level arrangement indium tin oxide (ITO)/perovskite interface, resulting in poor device performance. Here, a metal/insulator/n-type perovskite/p-type spiro-MeOTAD (MINP) structure is proposed to elaborate on the influence of the apparent work function and contact barrier change of the metal–semiconductor (MS) and metal–insulator–semiconductor (MIS) junction on the carrier transfer and collection. Common and easily available 5-amino-valeric acid is inserted into the ITO/perovskite interface to form an insulating dipole layer and to ensure quasi-ohmic contact at the front interface. Consequently, the device changes from Schottky/PN cascade heterojunction type to a single PN heterojunction device with its ideal factor decreasing from 3.35 to 2.05. Accordingly, the champion device achieves 19.37% PCE with significantly increased V _oc and FF compared to the pristine device. This work provides a facile and effective method to improve the application potential of novel ETL-free PSCs.

2D Perovskites

In article number 2102236, Jong Hyeok Park, Nam-Gyu Park, Hyunjung Shin and co-workers extract photo-generated holes from 3D bulk perovskites of FAPbI₃ through cyclohexylamonium-based 2D perovskites. 2D/3D perovskite heterojunction structures are successfully fabricated and the efficient extraction of holes is expressed in this cover picture.

An electron-withdrawing PZ-T unit is employed to incorporate into the PM6 polymer backbone as the third component, and a series of high-performance D-A₁-D-A₂ type terpolymers are synthesized by random copolymerization strategy. Among them, the PMZ-10:Y6-based polymer solar cells (PSCs) achieved an outstanding power conversion efficiency of 18.23%, which is the highest reported performance among the terpolymer-based PSCs so far.

Abstract

Recently, a random ternary copolymerization strategy has become a promising and efficient approach to develop high-performance polymer donors for polymer solar cells (PSCs). In this study, a low-cost electron-withdrawing unit, 2,5-bis(4-(2-ethylhexyl)thiophen-2-yl)pyrazine (PZ-T), is incorporated into the polymer backbone of PM6 as the third component, and three D-A₁-D-A₂ type terpolymers PMZ-10, PMZ-20, and PMZ-30 are synthesized by the random copolymerization strategy, with the PZ-T proportion of 10%, 20%, and 30%, respectively. The terpolymers exhibit downshifted highest occupied molecular orbital energy levels than PM6, which is beneficial for obtaining higher open-circuit voltage (V _oc) of the PSCs with the polymer as a donor. Importantly, the PSCs based on PMZ-10:Y6 demonstrate efficient exciton dissociation, higher and balanced electron/hole mobilities, desirable aggregation, and high power conversion efficiency of 18.23%, which is the highest efficiency among the terpolymer-based PSCs so far. The results indicate that the ternary copolymerization strategy with PZ-T as the second A-unit is an efficient approach to further improve the photovoltaic performance and reduce the synthetic cost of the D-A copolymer donors.

High-performance and ultra-stable self-powered photodetectors (PDs) based on perovskite nanowires (NWs) are achieved by using n-type conjugated polymer poly{2,5-bis(2-dodecylhexadecyl)-3,6-di(thiophen-2-yl)pyrrolo-[3,4-c]pyrrole-1,4(2H,5H)-dione-alt-(E)-1,2-bis(3-cyanothiophen-2-yl)ethene} as multi-functional interfacial layer. To the best of the authors’ knowledge, the performance and stability achieved herein represent the best results ever reported for perovskite PDs. More encouragingly, the application of NWs PDs for solution-processed reflective-mode pulse oximetry is also demonstrated.

Abstract

High-performance and long-term stable self-powered photodetectors (PDs) based on methylammonium lead iodide nanowires (NWs) are demonstrated by incorporating n-type conjugated polymer poly{2,5-bis(2-dodecylhexadecyl)-3,6-di(thiophen-2-yl)pyrrolo-[3,4-c]pyrrole-1,4(2H,5H)-dione-alt-(E)-1,2-bis(3-cyanothiophen-2-yl)ethene} (DPP-CNTVT) as multi-functional interfacial layer. Incorporating DPP-CNTVT with abundant Lewis base functional groups can effectively passivate under-coordinated Pb²⁺ defects, enabling perovskite NWs to exhibit remarkable stability and optoelectronic properties. Meanwhile, high electron mobility, together with the proper energy level of DPP-CNTVT, makes it ideal for use as an electron transport layer. Particularly, by taking advantage of the low bandgap of DPP-CNTVT, the utilization of low energy photons can be improved. The resulting PDs exhibit responsivity up to 0.50 A W⁻¹, specific detectivity approaching 10¹⁴ Jones, and a wide linear dynamic range of nearly 265 dB under zero bias operation, which represent the best results ever reported for self-powered perovskite PDs. More encouragingly, with the incorporation of an appropriate encapsulation layer, nearly 90% of the initial detectivity of PDs can be secured after 15 300 h of continuous operation in ambient conditions. The application of NWs PDs for solution-processed reflective-mode pulse oximetry is also demonstrated. This study provides valuable insights into developing efficient and ultra-stable self-powered perovskite PDs through interfacial engineering, which can accelerate the practical applications of this emerging technology.

An effective light-deflecting pattern is introduced to nonfullerene organic solar cells to improve energy conversion efficiency in the blue region. The normal incidence light is guided into a cavity-like chamber and mostly captured by the active layer, resulting in broadband absorption enhancement. The optimized device based on all A-D-A type nonfullerene acceptors achieves the highest reported efficiency of approaching 18%.

Abstract

Using narrow bandgap nonfullerene acceptors (NFAs) can broaden the absorption spectrum of organic solar cells (OSCs) to the near-infrared region. However, the simultaneously decreased extinction coefficient of the active layer at the blue region results in inevitable light escaping and energy loss. Herein, a blazed grating-based device configuration consisting of a patterned rear electrode is employed to compensate for the low absorption of nonfullerene OSCs. Experimental results reveal that the normal incidence light, especially blue light, that bounces off the patterned rear electrode is concentrated in a large tilted angle and subsequently trapped in waveguide mode. Along with the excitation of surface plasmon polariton, the structured nonfullerene OSCs using a new-designed PM6:M36 active layer obtain the broadband absorption enhancement with 1.5 times increase at the blue region. The optimized device achieves an 8.95% increase in photocurrent and a champion power conversion efficiency of approaching 18%, which is the highest reported value among all the devices based on A-D-A type NFAs.

In this work, the flexible monovalent spacer cations are introduced into the formamidinium-based low-dimensional perovskite, which effectively alleviates lattice distortion and reduce crystal defects. The resultant perovskite films possess desirable microscopic morphology, preferable crystal orientation, reduced defect states, and improved charge transport capability, which delivers highly efficient and thermostable perovskite solar cells.

Abstract

2D Dion–Jacobson (DJ) perovskite solar cells generally show mediocre device performances as they are restrained by their defective film quality. The rigid diammonium organic interlayer spacers are intolerant to lattice mismatches, which induces defects and distortions and ultimately deteriorates the optoelectronic properties. Herein, a secondary interlayer spacer is introduced into formamidinium (FA)-based low-dimensional perovskite, which substantially improves the film quality. The flexible monovalent spacer cations effectively alleviate lattice distortions and reduce crystal defects, providing perovskite films with desirable microscopic morphology, preferable crystal orientation, reduced defect states, and improved charge transport capability. As a result, the optimized perovskite solar cell based on the (PDA_0.9PA_0.2)(FA)₃Pb₄I₁₃ (PDA = propane-1,3-diammonium, PA = propylammonium) film exhibits the exceptional power conversion efficiency of 16.0%, the highest reported value in its class. In addition, the device demonstrates the enhanced thermal stability, retaining 90% of its initial efficiency after aging at 85 °C for 800 h.

Perovskite surface treatment by homologous bromide salts is investigated. It is found that bromides not only passivate surface defects but also penetrate into the perovskite providing bulk passivation. This leads to a large voltage of 1.24 V in a 1.63 eV bandgap device and an efficiency of 23.7% in a 1.56 eV bandgap device.

Abstract

The power conversion efficiency (PCE) of solution-processed organic–inorganic mixed halide perovskite solar cells has achieved rapid improvement. However, it is imperative to minimize the voltage deficit (W _oc = E _g/q − V _oc) for their PCE to approach the theoretical limit. Herein, the strategy of depositing homologous bromide salts on the perovskite surface to achieve a surface and bulk passivation for the fabrication of solar cells with high open-circuit voltage is reported. Distinct from the conclusions given by previous works, that homologous bromides such as FABr only react with PbI₂ to form a large-bandgap perovskite layer on top of the original perovskite, this work shows that the bromide also penetrates the perovskite film and passivates the perovskite in the bulk. This is confirmed by the small-bandgap enlargement observed by absorbance and photoluminescence, and the bromide element ratio increasing in the bulk by time-of-flight secondary-ion mass spectrometry and depth-resolved X-ray photoelectron spectroscopy. Furthermore, a clear suppression of non-radiative recombination is confirmed by a variety of characterization methods. This work provides a simple and universal way to reduce the W _oc of single-junction perovskite solar cells and it will also shed light on developing other high-performance optoelectronic devices, including perovskite-based tandems and light-emitting diodes.

Publication date: January 2022

Source: Nano Energy, Volume 91

Author(s): Xin Song, Po Sun, Dawei Sun, Yongchuan Xu, Yu Liu, Weiguo Zhu

A quite thick c-Si bottom-cell has to be used to fully absorb near-infrared photons, which greatly improves the cost of the perovskite/c-Si tandem solar cells (TSCs). The bifacial two-terminal TSCs can not only improve the energy output, but also significantly reduce the Si thickness while maintaining high efficiency.

Many studies have confirmed that the perovskite/crystalline silicon (c-Si) tandem solar cells (TSCs) can achieve excellent photovoltaic performance far exceeding that of single-junction solar cells. However, the quite thick c-Si bottom-cells have to be used to fully absorb near-infrared photons, which greatly improves the cost of the TSCs. The bifacial two-terminal TSCs not only can improve the energy output by introducing rear incident light, but also significantly reduce the Si thickness while maintaining high efficiency. Herein, the photovoltaic performance of bifacial perovskite/c-Si TSCs under different Si thicknesses, pyramid heights, and albedos have been calculated. It is found that the thickness of the c-Si sub-cells can be reduced from the current 250 to 25 μm, and only the albedos need to be increased by 18.6% to cover the absorption loss in the near-infrared. It is recommended that 100-μm thick c-Si is a suitable candidate and optimized the size of the Si pyramids (1.0 μm) to obtain excellent light trapping performance. This work can serve as a guidance for experimental preparation of low-cost and high-efficiency bifacial perovskite/c-Si TSCs.

High-efficiency ternary organic solar cells are fabricated using two nonfullerene acceptors DO-2F, IDTT-OB and one polymer donor PBDB-T. The introduction of IDTT-OB into PBDB-T:DO-2F can effectively optimize blend film morphology, improve charge dissociation and extraction, and suppress bimolecular recombination and nonradiative energy loss. The PBDB-T:DO-2F:IDTT-OB ternary device can achieve significantly enhanced power conversion efficiency of 14.09%.

Ternary strategy has been demonstrated to be an effective way to improve power conversion efficiency (PCE) of single-junction organic solar cells (OSCs). Herein, high-efficiency ternary OSCs are fabricated based on the PBDB-T:DO-2F binary system and acceptor IDTT-OB with asymmetric side chains as the third component. The introduction of nonfullerene acceptors (NFAs) IDTT-OB as a third component can efficiently increase the compatibility of the ternary system, reduce the crystallinity of DO-2F, optimize the blend film morphology, improve the charge transport and collection, suppress the bimolecular recombination, and reduce the nonradiative energy loss (ΔE _nonrad). Finally, the PBDB-T:DO-2F:IDTT-OB-based ternary device exhibits a high PCE of 14.09% with V _oc of 0.87 V, J _sc of 21.47 mA cm⁻², and fill factor of 75.70%, which is about 30% higher than the corresponding PBDB-T:DO-2F- and PBDB-T:IDTT-OB-based binary devices. Meanwhile, the ternary device also achieves a very low ΔE _nonrad of 0.22 eV. This work indicates that the ternary strategy can effectively optimize morphology of active layer, reduce nonradiative energy loss, and further improve photovoltaic performance of OSCs.

Residual PbI₂ at the bottom of perovskites can damage the efficiency and stability of fully-textured perovskite/silicon tandem solar cells. Here, a thermal-evaporated CsBr layer is introduced between the perovskite and hole transport layers to interact with residual PbI₂ and construct a gradient perovskite absorber for optimized energy level alignment. Tandem device efficiency of 27.48% and stability in nitrogen over 10 000 h are obtained.

Abstract

The perovskite/silicon tandem solar cell (PK/c-Si TSC) is a reasonable choice that can break through the efficiency limitations of silicon cells. Here, the p-i-n perovskite solar cell is conformally grown by the evaporation–solution combination technique on fully-textured silicon heterojunction cells to realize two-terminal PK/c-Si TSCs. Due to the adverse effect of the residual PbI₂ at the bottom of the perovskite bulk on device performance, a thermal-evaporated CsBr thin layer is introduced between the perovskite layer and the hole transport layer to construct a gradient perovskite absorber for optimized energy level alignment, so as to improve the open-circuit voltage and fill factor of the device. Finally, the PK/c-Si tandem cell achieves an efficiency of 27.48% and is stable in nitrogen over 10 000 h.

A high power conversion efficiency (PCE) of 15.2% is achieved by via a halogen-free, polymer donor in TPD-3:Y6-based organic solar cells, which is far higher than that of its fluorined counterpart, TPD-3F (11.4%). Comparative characterization including, transmission electron microscopy, grazing incidence wide-angle X-ray scattering, transient absorption, miscibility, measurements explain this result. Additionally, a PCE of 9.31% is achieved by TPD-3:Y6-based 20.4 cm² modules.

Abstract

Fluorination of the donor and/or acceptor blocks of photoactive semiconducting polymers is a leading strategy to enhance organic solar cell (OSC) performance. Here, the effects are investigated in OSCs using fluorine-free (TPD-3) and fluorinated (TPD-3F) donor polymers, paired with the nonfullerene acceptor Y6. Interestingly and unexpectedly, fluorination negatively affects performance, and fluorine-free TPD-3:Y6 OSCs exhibit a far higher power conversion efficiency (PCE = 14.5%) than in the fluorine-containing TPD-3F:Y6 blends (PCE = 11.5%). Transmission electron microscopy (TEM) analysis indicates that the TPD-3F:Y6 blends have larger phase domain sizes than TPD-3:Y6, which reduces exciton dissociation efficiency to 81% for TPD-3F:Y6 versus 93% for TPD-3:Y6. Additionally, grazing incidence wide-angle X-ray scattering (GIWAXS) reveals that the TPD-3F:Y6 blends are less textured than those of TPD-3:Y6, while space-charge limited currents reveal lower and unbalanced hole/electron mobility in TPD-3F:Y6 versus TPD-3:Y6 blends. Charge recombination dynamic, transient absorption, and donor–acceptor miscibility assays additionally support this picture. Furthermore, conventional architecture TPD-3:Y6 OSCs deliver a PCE of 15.2%, among the highest to date for halogen-free polymer donor OSCs. Finally, a large-area (20.4 cm²) TPD-3:Y6 blend module exhibits an outstanding PCE of 9.31%, one of the highest to date for modules of area >20 cm².

A vacuum deposited NdCl₃ interface layer (NdCl₃-IL) is used at the rear interface to suppress iodide ion migration. Compared to the control device, the NdCl₃-IL-based perovskite solar cells (PvSCs) show improved efficiency and negligible hysteresis, along with enhanced device stability. Combined with designed surface passivation, a PCE over 22% (certified value of 21.68%) can be achieved on large-area (1 cm²) PvSCs.

Abstract

Accurate interface engineering can effectively inhibit iodide ion migration, thereby improving the stability and photovoltaic performance of perovskite solar cells (PvSCs). The time-of-flight secondary-ion mass spectrometry reveals that in an aged n–i–p-type PvSC, the iodide ions will move toward the rear side and enter the FTO cathode. In this regard, the authors describe a simple thermal evaporation strategy for introducing an NdCl₃ interface layer (NdCl₃-IL) at the rear interface of perovskites to interdict the iodine ion migration pathway, leading to reduced trap densities throughout the whole perovskite region. As a result, a boosted open-circuit voltage (V _OC) is achieved, resulting in power conversion efficiency (PCE) up to 22.16% with negligible hysteresis. The NdCl₃-IL also enhances the device stability, maintaining 83% of initial PCE after the maximum-power-point tracking test for 100 h. More encouragingly, a certified PCE of 21.68% is demonstrated on a large-area (1 cm²) device with combined 2D/3D passivation strategies.

A dynamic strategy is proposed to fabricate high-quality perovskite films through resonance modulation, leading to a V _oc of 1.16 V and high power conversion efficiencies approaching 22.0% and 19.5% for small-area (0.09 cm²) and large-area (1.02 cm²) inverted perovskite solar cells (PSCs), respectively. More importantly, the unencapsulated PSCs exhibit excellent long-term stability under various environmental conditions (moisture, light, and heat).

Abstract

Manipulating perovskite crystallization to prepare high-quality perovskite films is the key to achieving highly efficient and stable perovskite solar cells (PSCs). Here, a dynamic strategy is proposed to modulate perovskite crystallization using a resonance hole-transporting material (HTM) capable of fast self-adaptive tautomerization between multiple electronic states with neutral and charged resonance forms for mediating perovskite crystal growth and defect passivation in situ. This approach, based on resonance variation with self-adaptive molecular interactions between the HTM and the perovskite, produces high-quality perovskite films with smooth surface, oriented crystallization, and low charge recombination, leading to high-performance inverted PSCs with power conversion efficiencies approaching 22% for small-area devices (0.09 cm²) and up to 19.5% for large-area devices (1.02 cm²). Also, remarkably high stability of the PSCs is observed, retaining over 90%, 88%, or 83% of the initial efficiencies in air with relative humidity of 40–50%, under continuous one-sun illumination, or at 75 °C annealing for 1000 h without encapsulation.

Doped p−n junctions represent the prototype of solar cells in text books, while p−i−n junctions support charge carrier collection for low-quality absorbers. For halide-perovskite cells the design via doping is challenging and substantial permittivity variations occur. The concept of the dielectric junction is introduced and designs electrostatics, recombination, and performance of solar cells by selecting materials with certain permittivities.

Conventional solar cells typically use doping of the involved semiconducting layers and work function differences between highly conductive contacts for the electrostatic design and the charge selectivity of the junction. In some halide perovskite solar cells, however, substantial variations in the permittivity of different organic and inorganic semiconducting layers strongly affect the electrostatic potential and thereby indirectly also the carrier concentrations, recombination rates, and eventually efficiencies of the device. Here, numerical simulations are used to study the implications of electrostatics on device performance for classical p−n junctions and p−i−n junctions, and for device geometries as observed in perovskite photovoltaics, where high-permittivity absorber layers are surrounded by low-permittivity and often also low-conductivity charge transport layers. The key principle of device design in materials with sufficiently high mobilities that are still dominated by defect-assisted recombination is the minimization of volume with similar densities of electrons and holes. In classical solar cells this is achieved by doping. For perovskites, the concept of a dielectric junction is proposed by the selection of charge transport layers with adapted permittivity if doping is not sufficient.

The hydrophobic Er@C₈₂ is a bifunctional additive to the 2,2′,7,7′-tetrakis-(N,N-di-p-methoxyphenylamino)-9,9′-spirobifluorene (Spiro-OMeTAD) hole transport layer that can enhance the photovoltaic performance and the stability of perovskite solar cells (PSCs) simultaneously.

Perovskite solar cells (PSCs) based on 2,2′,7,7′-tetrakis-(N,N-di-p-methoxyphenylamino)-9,9′-spirobifluorene Spiro-OMeTAD hole transport layer (HTL) have achieved a huge success in power conversion efficiency (PCE), but the required lithium bis(trifluoromethanesulfonyl)imide (Li-TFSI) dopant in Spiro-OMeTAD HTL is hygroscopic, not only impairing the charge transport but also inducing the instability of PSCs. Herein, Er@C₈₂, which consists of a hydrophobic fullerene cage encapsulating an Er³⁺ ion, is first introduced as a novel additive to modify the Li-TFSI-based Spiro-OMeTAD HTL. By adding a tiny amount of Er@C₈₂ (0.09 mg mL⁻¹) in the Spiro-OMeTAD HTL, the PSC exhibits an efficiency promotion from 17.53% to 19.22%. The PCE enhancement is mainly attributed to the improved film quality of HTL after adding Er@C₈₂, which promotes the oxidation of Spiro-OMeTAD, resulting in faster hole transport and less charge recombination. Simultaneously, the hydrophobic Er@C₈₂ and the improved film quality of HTL lead to a dramatically enhanced stability of PSCs. Accordingly, the Er@C₈₂-modified devices can maintain over 70% and 80% of the initial efficiencies after exposure in air for 400 h and in an Ar atmosphere for 2000 h, respectively. Therefore, this bifunctional Er@C₈₂ additive provides a promising pathway for fabricating highly efficient and stable PSCs.

An efficient strategy is proposed to accurately adjust the Sn content and Sn-related defects by tuning the selenization pressure from 0.4 to 1.3 atm. A champion device fabricated at the optimal selenization pressure (0.7 atm) exhibits a power conversion efficiency of 11.32% with a V _OC of 0.496 V.

In spite of the merits such as Earth abundance and high performance, Cu₂ZnSn(S,Se)₄ (CZTSSe) solar cells suffer from unfavorable Sn_Zn antisite defects and complexes, which act as nonradiative recombination centers and deteriorate the open-circuit voltage (V _OC). Therefore, the management of Sn composition is the prerequisite for achieving high-efficiency CZTSSe photovoltaic devices. At present, the Sn-related composition and defect modifications at different selenization pressures remain unclear, which restrain the development of efficient kesterite solar cells. Herein, a facile yet effective strategy to accurately adjust the Sn content in CZTSSe films by simply optimizing the selenization pressure is demonstrated. Compared with the widely used atmospheric pressure, it is unveiled that the appropriate negative pressure (0.7 atm) can tailor the optimal Sn content in the absorber layer, influencing both the Sn-related defects and the microstructures. In contrast, a lower (0.4 atm) and a higher (1.3 atm) selenization pressure results in undesirable deep Cu_Sn defects and a Sn(S,Se)₂ secondary phase, respectively. A champion device fabricated at this optimal selenization pressure (0.7 atm) exhibits a power conversion efficiency of 11.32% with a V _OC of 0.496 V. This study paves the path toward highly efficient kesterite solar cells by tailoring the composition-dependent defects.

Perovskite Solar Cells

In article number 2100401, Iván Mora-Seró, Rajan Jose, and co-workers present a roadmap for the perovskite solar cells via a 5S (Stability, Safety, Scalability, Sustainability, and Storage) analysis. Application driven, instead of performance driven, developments are shown to favor their commercialization.

Perovskite quantum dots (QDs) display the quantum confinement effect yet maintain the characteristics of bulk materials. In this Review the advantages and disadvantages of perovskite QDs and significant strategies (exchange chemistry, passivation engineering, and structure engineering) for the advancement of perovskite solar cells with perovskite QDs as an absorber are discussed.

Abstract

Perovskite quantum dots (QDs) preserve the attractive properties of perovskite bulk materials and present additional advantages, owing to their quantum confinement effect, leading to their suitability as an absorber in perovskite solar cells. In this Review, the issues and advantages of perovskite QDs are analyzed in the context of purification, device fabrication with perovskite QDs, light absorption, charge transport, and stability. In addition, promising strategies to enhance perovskite QDs and QD-based solar cells are elucidated based on exchange chemistry (ion and ligand exchange), passivation engineering (ion and ligand passivation), and structure engineering (conventional/inverted, planar/mesoscopic and dimensionally graded structures). These discussions will give a clue to the further development of perovskite QDs and thus the advancement of QD-based solar cells.

Photovoltaics

In article number 2102246 Felix Lang, Giles E. Eperon, Samuel D. Stranks and co-workers investigate efficient all perovskite-based tandem photovoltaics. This class of photovoltaics combine high specific power with good tolerance to the harsh radiation environment in space, thereby promising a next-generation of lightweight and cost-efficient solutions to power private space exploration, low-cost missions as well as future habitats on the Moon and Mars.