Chen Weijie

Publication date: 18 November 2020

Source: Joule, Volume 4, Issue 11

Author(s): Shaun Tan, Ilhan Yavuz, Marc H. Weber, Tianyi Huang, Chung-Hao Chen, Rui Wang, Hao-Cheng Wang, Jeong Hoon Ko, Selbi Nuryyeva, Jingjing Xue, Yepin Zhao, Kung-Hwa Wei, Jin-Wook Lee, Yang Yang

Recent advances in near‐infrared‐transparent perovskite and perovskite‐based tandem solar cells are reviewed. The factors limiting their performance, and strategies for further improvement are discussed. The challenges limiting their commercialization and outlook for technology advancements are presented.

Abstract

Metal halide perovskite solar cells (PSCs) have gained tremendous attention due to their high power conversion efficiencies (PCEs) and potential for low‐cost manufacturing. Their wide and tunable bandgap makes perovskites an ideal candidate for tandem solar cells (TSCs) with well‐established narrow bandgap photovoltaic technologies, such as crystalline silicon and Cu(In,Ga)Se₂, to boost the PCEs beyond the Shockley–Queisser limit at affordable additional cost. Although perovskite‐based TSCs have shown rapid progress over the past few years, they are far from reaching their practical efficiency limit. In addition, technology commercialization needs to overcome several challenges such as processing upscalability and long‐term operational stability of solar modules. In this review, a comprehensive overview of the recent progress of perovskite‐based TSCs is provided and the key challenges in the field are discussed. First, the structural and optoelectronic properties of metal halide perovskite materials and preparation methods of metal halide perovskite layers are introduced. Next, the important constituents of near‐infrared (NIR) transparent PSCs for achieving high efficiency along with high NIR transmittance are highlighted. Then the developments in perovskite‐based TSCs are reviewed, the limiting factors are outlined, and strategies to boost the efficiencies well beyond 30% are provided. Finally, the review is concluded by highlighting the bottlenecks for commercialization and providing an outlook for technology advancement.

A series of phenylhydroxylammonium halide salts is adopted to passivate the surface of the mixed perovskite film, resulting in enormously enhanced photoluminescence (PL) intensity and prolonged carrier lifetime. As a result, the best perovskite solar cell treated with phenylbutylammonium bromide realizes a power conversion efficiency (PCE) of 22.67% with a V _oc of 1.216 V, corresponding to a small V _oc deficit of ≈344 mV.

Abstract

Suppressing non‐radiative recombination via passivating surface defects of perovskite films has demonstrated an excellent strategy for high‐performance perovskite solar cells (PSCs). However, it is still hard to realize both high open‐circuit voltage (V _oc) of >1.2 V and high power conversion efficiency (PCE) of >22%, because the optimized bandgap of perovskite films is less than 1.60 eV for efficient light harvesting and V _oc deficit is generally unavoidable due to carriers recombination. Here, the surface of the perovskite film is treated with a series of phenylhydroxylammonium halide salts and it is found that all of them can remarkably prolong the carrier lifetime owing to their excellent capability of surface defects passivation. The best PSC with phenylbutylammonium bromide treatment realizes a PCE of 22.67% with a V _oc of 1.216 V, corresponding to a small V _oc deficit of ≈344 mV.

In this paper, the development and preparation methods of graphene materials are summarized, and the applications of graphene and its derivatives in perovskite solar cells are reviewed, including defect passivation, ion migration blocking, and charge transport optimization. The progress of graphene as electrode materials in semitransparent and flexible devices is also summarized.

Abstract

Perovskite solar cells (PSCs) have attracted much attention due to their high efficiency and low manufacturing cost. However, the defects in perovskite films and the instability issue caused by ion migration limit the further improvement of its efficiency and stability. Graphene and its derivatives are potential materials to solve these problems due to their rich functional groups, environmental stability and compactness, which triggered extensive researches in recent years. In this paper, the development and preparation methods of graphene materials are summarized and then their applications in PSCs are reviewed, with particular emphasis on their function of blocking ion migration.

A generally applicable sequential deposition (SD) strategy is developed to construct high‐performance organic solar cells (OSCs) without involving complicated procedures for morphological control. The SD‐processed OSCs via simple adjustment of the acceptor layer to impact the blend phase can afford higher efficiencies than their conventional OSC counterparts, providing an avenue toward promoting better photovoltaic performance and reducing production requirements.

Abstract

Bulk‐heterojunction (BHJ) organic solar cells (OSCs) are prepared by a common one‐step solution casting of donor‐acceptor blends often encounter dynamic morphological evolution which is hard to control to achieve optimal performance. To overcome this hurdle, a generally applicable, sequential processing approach has been developed to construct high‐performance OSCs without involving tedious processes. The morphology of photoactive layers comprising a polymer donor (PM6) and a nonfullerene acceptor (denoted as Y6‐BO) can be precisely manipulated by tuning Y6‐BO layer with a small amount of 1‐chloronaphthalene additive to induce the structural order of Y6‐BO molecules to impact the blend phase. The results of a comparative investigation elucidate that such two‐step procedure can afford more favorable BHJ microstructure than that achievable with the single blend‐casting route. This translates into improved carrier generation and transport, and suppressed charge recombination. Consequently, the devices based on sequential deposition (SD) deliver a remarkable efficiency up to 17.2% (the highest for SD OSCs to date), outperforming that from the conventional BHJ devices (16.4%). The general applicability of this approach has also been tested on several other nonfullerene acceptors which show similar improvements. These results highlight that SD is a promising processing alternative to promote better photovoltaic performance and reduce production requirements.

As a key factor affecting the performance and stability of perovskite solar cells, the application of the interface layer is crucial. This review summarizes that ultra‐dense and stable metal oxide layers can be prepared by atomic layer deposition for application in perovskite solar cells, and their commercial feasibility is prospected.

Abstract

In recent years, the development of perovskite solar cells (PSCs) is advancing along the way, and the efficiency is comparable to traditional silicon‐based solar cells. However, as crucial factors in the road to commercialization, stability and upscaling manufacture have not been fully investigated yet. To solve these problems, the exploration of charge transport layer (CTL) is clearly imminent, which is critical to the stability of PSCs. Among them, inorganic metal oxides have better stability than organic CTL. Particularly, the atomic layer deposition (ALD) process can fabricate dense and scalable metal oxides based on the self‐limiting surface reaction. This perspective focuses on the recent progress of ALD‐grown metal oxides in PSCs: both of electron and hole transport layer; connection layer in tandem architectures; application in semi‐transparent perovskite solar cells (ST‐PSCs); prospective of commercialization feasibility of the ALD‐grown metal oxides in ST‐PSCs.

The inorganic salt of potassium thiocyanate plays a triple passivation role at the interface between NiO _x hole transport layer and perovskite by strong covalent band and electrostatic force. It can reduce the interface defects and promote carrier extraction and transportation, which leads to high efficiency and good stability. This provides a promising multiple passivation strategy for improving perovskite solar cells performance.

Abstract

Inverted perovskite solar cells (PSCs) are still suffering low power conversion efficiency because of hole accumulation and trap‐assisted non‐radiative recombination at the interface originating from the large energy offset, interface defects, and rough contact. Here, a triple passivation of the two in‐between surfaces of the hole transport layer (HTL) and perovskite is proposed. The inorganic salt of potassium thiocyanate (KSCN) is introduced to simultaneously cross‐link NiO _x , HTL, and methylammonium lead iodide (MAPbI₃), which can significantly improve both device performances and stability. In addition to potassium passivation, the thiocyanate shows two good passivation effects on perovskite and NiO _x to achieve the triple passivation. The strong NiN bonding exhibits strong polar covalent bond properties to make the electron deviate from the Ni side. Meanwhile, the strong electrostatic force between S and Pb in MAPbI₃ makes the Pb atomic layer closer to perovskite to restrain the I atom. Meanwhile, the KSCN modification leads to better valence band alignment. Eventually, the KSCN meditated PSCs exhibit both high efficiency of 21.23% with open‐circuit voltage of 1.14 V and improved operational stability. The demonstration of triple interface passivation contributes to establishing promising multiple passivation strategies for improving the demanding PSC performances and stability.

Although high‐efficiency perovskite solar cells (PSCs) are typically fabricated in a glovebox, strategies to fabricate PSCs in ambient conditions hold many advantages and are often overlooked. Importantly, high‐efficiency ambient PSCs can only be achieved if specific adaptations to their processing conditions are made. This review provides important design rules to fabricate efficient PSCs in ambient conditions.

Abstract

Organic–inorganic hybrid perovskite solar cells (PSCs) have attracted significant attention in recent years due to their high‐power conversion efficiency, simple fabrication, and low material cost. However, due to their high sensitivity to moisture and oxygen, high efficiency PSCs are mainly constructed in an inert environment. This has led to significant concerns associated with the long‐term stability and manufacturing costs, which are some of the major limitations for the commercialization of this cutting‐edge technology. Over the past few years, excellent progress in fabricating PSCs in ambient conditions has been made. These advancements have drawn considerable research interest in the photovoltaic community and shown great promise for the successful commercialization of efficient and stable PSCs. In this review, after providing an overview to the influence of an ambient fabrication environment on perovskite films, recent advances in fabricating efficient and stable PSCs in ambient conditions are discussed. Along with discussing the underlying challenges and limitations, the most appropriate strategies to fabricate efficient PSCs under ambient conditions are summarized along with multiple roadmaps to assist in the future development of this technology.

In this contribution, the photovoltaic performance of methylammonium‐free perovskite solar cells is enhanced by constructing interfacial capping layers with a pair of alkylammonium halides. The structure and composition of the interfacial layers are comprehensively investigated and their correlation with the device performance is described in terms of defect passivation efficacy, energy level alignment, and hydrophobicity for moisture resistance.

Abstract

The methylammonium (MA)‐free perovskite solar cells (PSCs) have drawn broad attention due to their excellent thermostability. However, the efficiency of these devices is inferior to most state‐of‐the‐art PSCs. Herein, the photovoltaic performance of the MA‐free PSCs is enhanced by constructing interfacial capping layers with a pair of alkylammonium halides, n‐propylammonium (PA) iodide and propane‐1,3‐diammonium (PDA) iodide. The structure and composition of the interfacial layers are comprehensively investigated and their correlation with the device performance is presented in terms of defect passivation efficacy, energy level alignment, and hydrophobicity for moisture resistance. The PSC devices based on the PAI and PDAI₂ treated MA‐free perovskite films demonstrate better power conversion efficiencies (PCEs) and stabilities than the reference devices without the interfacial layers. Although the PAI‐treated devices exhibit the highest PCE of 21.1%, the PDAI₂‐treated PSCs demonstrate the exceptional thermal and humidity stabilities.

A naphthalene diimide based double‐cable conjugated polymer provided a record efficiency of 8.4 % in single‐component organic solar cells. It simultaneously facilitates exciton separation and charge transport via miscibility control.

Abstract

A record power conversion efficiency of 8.40 % was obtained in single‐component organic solar cells (SCOSCs) based on double‐cable conjugated polymers. This is realized based on exciton separation playing the same role as charge transport in SCOSCs. Two double‐cable conjugated polymers were designed with almost identical conjugated backbones and electron‐withdrawing side units, but extra Cl atoms had different positions on the conjugated backbones. When Cl atoms were positioned at the main chains, the polymer formed the twist backbones, enabling better miscibility with the naphthalene diimide side units. This improves the interface contact between conjugated backbones and side units, resulting in efficient conversion of excitons into free charges. These findings reveal the importance of charge generation process in SCOSCs and suggest a strategy to improve this process: controlling miscibility between conjugated backbones and aromatic side units in double‐cable conjugated polymers.

Antisolvent engineering is employed to tune the crystal nucleation and grain growth of perovskite for achieving efficient perovskite solar cells. The engineering of perovskites treated with the green antisolvent MABr‐Eth, suppressing defects‐induced nonradiative recombination in perovskite solar cells, is developed. As expected, the device delivers over 21% power conversion efficiency and a better storage and light‐soaking stability.

Abstract

Organic–inorganic hybrid perovskites have attracted considerable attention due to their superior optoelectronic properties. Traditional one‐step solution‐processed perovskites often suffer from defects‐induced nonradiative recombination, which significantly hinders the improvement of device performance. Herein, treatment with green antisolvents for achieving high‐quality perovskite films is reported. Compared to defects‐filled ones, perovskite films by antisolvent treatment using methylamine bromide (MABr) in ethanol (MABr‐Eth) not only enhances the resultant perovskite crystallinity with large grain size, but also passivates the surface defects. In this case, the engineering of MABr‐Eth‐treated perovskites suppressing defects‐induced nonradiative recombination in perovskite solar cells (PSCs) is demonstrated. As a result, the fabricated inverted planar heterojunction device of ITO/PTAA/Cs_0.15FA_0.85PbI₃/PC₆₁BM/Phen‐NADPO/Ag exhibits the best power conversion efficiency of 21.53%. Furthermore, the corresponding PSCs possess a better storage and light‐soaking stability.

In tandem organic photovoltaics, most ultraviolet–visible photons are absorbed by the front sub‐cell, so in the rear sub‐cell, excitons generated on large‐bandgap donors will be reduced significantly. This reduces the conductivity and limits the hole‐transporting property of the rear sub‐cell. An infrared‐absorbing polymer donor is introduced, which provides a second hole‐generation/transporting mechanism to minimize the aforementioned detrimental effects.

Abstract

In tandem organic photovoltaics, the front subcell is based on large‐bandgap materials, whereas the case of the rear subcell is more complicated. The rear subcell is generally composed of a narrow‐bandgap acceptor for infrared absorption but a large‐bandgap donor to realize a high open‐circuit voltage. Unfortunately, most of the ultraviolet–visible part of the photons are absorbed by the front subcell; as a result, in the rear subcell, the number of excitons generated on large‐bandgap donors will be reduced significantly. This reduces the (photo) conductivity and finally limits the hole‐transporting property of the rear subcell. In this work, a simple and effective way is proposed to resolve this critical issue. To ensure sufficient photogenerated holes in the rear subcell, a small amount of an infrared‐absorbing polymer donor as a third component is introduced, which provides a second hole‐generation and transporting mechanism to minimize the aforementioned detrimental effects. Finally, the short‐circuit current density of the two‐terminal tandem organic photovoltaic is significantly enhanced from 10.3 to 11.7 mA cm⁻² (while retaining the open‐circuit voltage and fill factor) to result in an enhanced power conversion efficiency of 15.1%.

A narrow‐bandgap polymer acceptor L14 with an acceptor–acceptor (A–A) backbone is synthesized, showing lower‐lying frontier molecular orbitals, higher electron mobility, and larger absorption coefficient without sacrificing photovoltage compared to its donor–acceptor (D–A) analog polymer, L11. When applied in all‐polymer solar cells, L14 yields an outstanding efficiency of 14.3%.

Abstract

Narrow‐bandgap polymer semiconductors are essential for advancing the development of organic solar cells. Here, a new narrow‐bandgap polymer acceptor L14, featuring an acceptor–acceptor (A–A) type backbone, is synthesized by copolymerizing a dibrominated fused‐ring electron acceptor (FREA) with distannylated bithiophene imide. Combining the advantages of both the FREA and the A–A polymer, L14 not only shows a narrow bandgap and high absorption coefficient, but also low‐lying frontier molecular orbital (FMO) levels. Such FMO levels yield improved electron transfer character, but unexpectedly, without sacrificing open‐circuit voltage (V _oc), which is attributed to a small nonradiative recombination loss (E _loss,nr) of 0.22 eV. Benefiting from the improved photocurrent along with the high fill factor and V _oc, an excellent efficiency of 14.3% is achieved, which is among the highest values for all‐polymer solar cells (all‐PSCs). The results demonstrate the superiority of narrow‐bandgap A–A type polymers for improving all‐PSC performance and pave a way toward developing high‐performance polymer acceptors for all‐PSCs.

High‐performance quasi‐2D perovskite solar cells (PVSCs) are demonstrated via heat–light co‐treatment. The optimized quasi‐2D PVSC presents a maximum PCE of 18.24% with excellent stability. The underlying mechanism of the light and heat co‐treatment in improving the device performance lies in its synergistic effect in reducing the trap states and improving the charge transport.

Abstract

2D perovskite solar cells (2D PVSCs) show good stability for commercialization. However, their power conversion efficiency (PCE) is relatively low. In this work, a post‐treatment strategy by simultaneously applying light and heat to quasi‐2D PVSCs, obtaining a record PCE of 18.24% is developed. It is found that heat‐treating PVSCs in the dark slightly increases the device performance over time at temperatures below 75 °C, whereas the performance deteriorates rapidly at temperatures above 100 °C. Upon illumination, the device efficiency is significantly improved, particularly when the thermal‐treatment temperature is increased to 100 °C. A comprehensive carrier dynamic study reveals that the enhanced performance can be attributed to the reduced quasi‐2D perovskite defect states and improved charge collection. In addition, this strategy enables better stability, and an unencapsulated device can retain 90% of its original PCE after 1340 h of direct exposure to air with a humidity of 50 ± 5%. Thus, the strategy paves the way for the commercialization of quasi‐2D PVSCs.

Three benzo[1,2‐b:4,5‐b']dithiophene‐thienothiophene π‐bridged N‐octylthieno[3,4‐c]pyrrole‐4,6‐dione‐based polymer donors named as PBDT‐X (X=H, F, Cl) are developed. While a planar accepting unit helps improve the crystallinity, all three photovoltaic parameters are simultaneously increased with the introduction of halogen atoms. PBDT‐Cl:Y6‐based devices yield an efficiency of 15.63%, attributed to the enhanced crystallinity, hole mobility, and domain purity.

Abstract

In this work, a new series of polymer donors consisting of thienothiophene π‐bridged N‐octylthieno[3,4‐c]pyrrole‐4,6‐dione (8ttTPD) and benzo[1,2‐b:4,5‐b']dithiophene (BDT) units for producing highly efficient organic solar cells (OSCs) paired with a Y6 acceptor is developed. The incorporation of the highly planar 8ttTPD unit enhances crystalline properties as well as hole mobilities of the BDT‐based polymers that typically have amorphous features. Further, the 2D side chains with halogen atoms (fluorine and chlorine) are designed as another handle to control the crystallinity and energy levels of the BDT‐based polymer donors: PBDT‐X (X = H, F, or Cl). Synergistic effects of incorporated 8ttTPD unit and the halogenated 2D side chain generate significantly enhanced charge transport and recombination properties of the OSCs, which is mainly attributed to optimized crystallinity and hole mobility of the polymer donors. Therefore, the PBDT‐Cl:Y6‐based OSCs exhibit the highest power conversion efficiency (PCE) of 15.63% with simultaneous improvements of open‐circuit voltage, short‐circuit current density, and fill factor, which outperforms the PCEs of PBDT‐H:Y6 (11.84%) and PBDT‐F:Y6 (14.86%).

Three new dithieno[2,3‐d;2ʹ,3ʹ‐dʹ]benzo[1,2‐b;4,5‐bʹ]dithiophene based small‐molecule donors with different branching points for alkyl side chains are designed and synthesized for all small molecular organic solar cells. Modifying the branching points tunes the properties in the aggregation state, and an optimal nanofiber‐based hierarchical morphology for efficient charge separation and transport is successfully demonstrated.

Abstract

The optimization of bulk heterojunction morphology is one of the most challenging topics in all‐small‐molecule organic solar cells. Herein, three small molecular donors based on dithieno[2,3‐d;2′,3′‐d′]benzo[1,2‐b;4,5‐b′]dithiophene (DTBDT) unit by systematically moving the branching point of the alkyl chain have been designed, synthesized, and applied in organic solar cells. Modifying the branching points enables the properties of the aggregation state to be tuned, and an efficient nanofiber‐based hierarchical morphology is successfully demonstrated by combining with different nonfullerene acceptors. The molecules with far branching points can form nanofibers in active layers, and theses nanofibers help the charge separation and charge transport in a large donor‐rich or acceptor‐rich domain of approximately 100 nm. Using nonfullerrene Y6 as an acceptor, the highest power conversion efficiency of 14.78% is obtained, which is one of the highest efficiencies in all‐small‐molecule organic solar cells. The strategy of modification of alkyl side chain branching points can be a practical way to actualize crystallinity control and active layer morphology for improving the performance of all‐small‐molecule organic solar cells.

N‐functionalized conjugation engineering is explored for the design of 2D asymmetric nonfullerene acceptors (NFAs). Endowed with high charge transport and good nanofibrous phase separation with PBDB‐T, the best‐performing NFA contributes a champion power conversion efficiency of 14.02% in solar cells. Excellent thermal aging and light soaking stability are observed for the corresponding solar cells.

Abstract

The charge transport and morphology of active layers are key considerations for device performance and stability in organic solar cells (OSCs). Such properties can be fine‐tuned via elaborate molecular design of fused‐ring electron acceptors (FREAs), especially conjugation extension and side chain engineering. In this work, N‐functionalized conjugation is explored in the design of high‐efficient asymmetric FREAs. The twisting of N‐conjugated side chains from backbone endows three FREAs with similar energy levels and light absorptions (≈850 nm edge). Their blends with PBDB‐T exhibit high charge carrier mobility and ordered phase separation. Excitingly, IPT2F‐TT based OSCs yield a champion power conversion efficiency (PCE) of 14.02% with a fill factor (FF) of 75.06%, outperforming PBDB‐T devices with IPT2F‐Th (12.52%, 71.20%), IPT2F‐Ph (13.13%, 72.11%), and octylated IPT‐2F (13.70%, 71.50%). The PCE over 14% and FF over 75% are among the highest values for 2D FREAs OSCs reported to date. More importantly, outstanding thermal stability and light soaking stability are observed with PCE over 12% maintained after thermal or light aging for 100 h. This work demonstrates N‐conjugated FREAs design as an effective strategy to simultaneously improve the photovoltaic performance and device stability for the OSCs.

A coherent interface of PMA₂PbI₄ and FAPbI₃ induces epitaxial growth of α‐FAPbI₃. Facilitated formation of α‐FAPbI₃ at low temperature results in minimal structural disorder and enhanced charge‐carrier transport properties. A perovskite solar cell based on PMA₂PbI₄ and Cs_0.02FA_0.98PbI₃ exhibits an efficiency of 21.25% and stabilized efficiency of 19.95%.

Abstract

Low dimensional (LD) perovskite materials generally exhibit superior chemical stability against ambient moisture and thermal stress than that of 3D perovskites. Recently, LD perovskite has been used as a passivation layer on the surface of 3D perovskite grains. Although various LD perovskites have been developed focusing on their hydrophobicity, the impact of crystal structure of LD perovskite on the photovoltaic performance of perovskite solar cell (PSC) is still uncertain. In this work, the effects of the structural characteristics of LD perovskites on the crystal formation of formamidinium lead triiodide (α‐FAPbI₃) and on the optoelectrical properties of PSCs are elucidated. The phase‐transformation kinetics of FAPbI₃ mixed with LD perovskites is studied using the Johnson–Mehl–Avrami–Kolmogorov model. It is found that the arrangement of PbI₆ octahedra in the LD perovskite changes the rate of α‐FAPbI₃ formation. Facilitated nucleation of α‐FAPbI₃ at the LD/FAPbI₃ interface results in minimal structural disorder and prolonged charge‐carrier lifetimes. As a result, the PSC with the optimized LD perovskite structure exhibits a power conversion efficiency of 21.25% from a reverse current–voltage scan, and stabilized efficiency of 19.95% with excellent ambient stability without being encapsulated.

This work introduces a morphology engineering method to prepare low‐temperature processed TiO₂ layer for perovskite devices. The morphology of TiO₂ layer can be controlled using a spray coating strategy, which can manipulate the growth of perovskite layer. Combining the spray coating technique and a metal ion doping strategy, a perovskite photovoltaic with efficiency over 21% can be obtained.

Abstract

Perovskite solar cells (PSCs) have become one of the most promising renewable energy converting devices. However, in order to reach a sufficiently high power conversion efficiency (PCE), the PSCs typically require a high‐temperature sintering process to prepare mesostructured TiO₂ as an efficient electron transport layer (ETL), which prohibits the PSCs from commercialization in the future. This work investigates a low‐temperature synthesis of TiO₂ nanocrystals and introduces a two‐fluid spray coating process to produce a nanostructured ETL for the following deposition of perovskite layer. The temperature during the whole deposition process can be maintained under 150 °C. Compared to the typical planar TiO₂ layer, the perovskite layer fabricated on a nanostructured TiO₂ layer shows uniform compactness, preferred orientation, and high crystallinity, leading to reproducible and promising device performance. The detail mechanisms are revealed by the contact angle test, morphology characterization, grazing incident wide angle X‐Ray scattering measurement, and space charge limited currents analysis. Finally, optimized device performance can be achieved through adequate Zn doping in the TiO₂ layer, demonstrating an average PCE of 19.87% with champion PCE of 21.36%. The efficiency can maintain over 80% of its original value after 3000 h storage in ambient atmosphere. This study suggests a promising approach to offer high‐efficiency PSCs using the low‐temperature process.

A multifunctional interface layer is formed on perovskite film through establishing perovskite as the ligand on PbS quantum dots (QDs). The multifunctions are strong interactions of PbS QDs with perovskites particularly at the grain boundaries, an inhibition of iodide ions mobilization, and the reduction of the dangling bonds of Pb²⁺. Finally, the perovskite device efficiency and stability are highly improved.

Abstract

While organic–inorganic halide perovskite solar cells (PSCs) show great potential for realizing low‐cost and easily fabricated photovoltaics, the unexpected defects and long‐term stability against moisture are the main issues hindering their practical applications. Herein, a strategy is demonstrated to address the main issues by introducing lead sulfide quantum dots (QDs) on the perovskite surface as the multifunctional interface layer on perovskite film through establishing perovskite as the ligand on PbS QDs. Meanwhile, the multifunctions are featured in three aspects including the strong interactions of PbS QDs with perovskites particularly at the grain boundaries favoring good QDs coverage on perovskites for ultimate smooth morphology; an inhibition of iodide ions mobilization by the strong interaction between iodide and the incorporated QDs; and the reduction of the dangling bonds of Pb²⁺ by the sulfur atoms of PbS QDs. Finally, the device performances are highly improved due to the reduced defects and non‐radiative recombination. The results show that both open‐circuit voltage and fill factor are significantly improved to the high values of 1.13 V and 80%, respectively in CH₃NH₃PbI₃‐based PSCs, offering a high efficiency of 20.64%. The QDs incorporation also enhances PSCs’ stability benefitting from the induced hydrophobic surface and suppressed iodide mobilization.

The roles of small alkali metals on the stability of Sn perovskites are investigated by theoretical calculations and controlled experiments. K⁺ incorporation can enhance the Sn‐based perovskites by reducing structural instability and unintentional hole doping.

Sn‐based halide perovskites are the most promising alternatives for developing Pb‐free perovskite solar cell materials. However, the stability of Sn halide perovskites is the biggest concern for future developments. The phase stability and the doping‐level control should be resolved for Sn perovskites to compete with Pb‐based analogs. Herein, interstitial engineering is used to enhance the stability of Sn‐based halide perovskites using alkali metals through ab initio calculations and controlled experiments. This study reveals that alkali metal interstitials can promote the performance of Sn perovskites by controlling their phase stability, suppressing free carrier density, and locking lattice vibration. K⁺ shows the most promising behavior among alkali–metal cations in terms of phase stabilization and defect formation energy.

Quartz‐based perovskite solar cells maintain 19% power conversion efficiency after irradiation with high doses of 1 MeV electrons. Time‐resolved microwave conductivity measurements reveal only a marginal reduction in charge carrier diffusion length after high doses of high energy electron irradiation.

Metal halide perovskite solar cells (PSCs) are of interest for high altitude and space applications due to their lightweight and versatile form factor. However, their resilience toward the particle spectrum encountered in space is still of concern. For space cells, the effect of these particles is condensed into an equivalent 1 MeV electron fluence. The effect of high doses of 1 MeV e‐beam radiation up to an accumulated fluence to 10¹⁶ e⁻ cm⁻² on methylammonium lead iodide perovskite thin films and solar cells is probed. By using substrate and encapsulation materials that are stable under the high energy e‐beam radiation, its net effect on the perovskite film and solar cells can be studied. The quartz substrate‐based PSCs are stable under the high doses of 1 MeV e‐beam irradiation. Time‐resolved microwave conductivity analysis on pristine and irradiated films indicates that there is a small reduction in the charge carrier diffusion length upon irradiation. Nevertheless, this diffusion length remains larger than the perovskite film thickness used in the solar cells, even for the highest accumulated fluence of 10¹⁶ e⁻ cm⁻². This demonstrates that PSCs are promising candidates for space applications.