JIANG ZHI XUAN

Inorganic CsPbI3 perovskite is the most competitive candidate to hybrid perovskites. However, its poor phase stability, hydrophobicity and high‐density defects have limited the development of CsPbI3 perovskite solar cells (PSCs). To overcome these obstacles for achieving high‐performance CsPbI3 PSCs, additive engineering has been widely employed. Herein, the progress of additive engineering in CsPbI3 PSCs is systematically reviewed.

All‐inorganic perovskite solar cells (PSCs) have attracted a lot of attention in the past few years because of their preeminent thermal stability compared with organic–inorganic hybrid PSCs. Among all kinds of all‐inorganic perovskites, CsPbI₃ perovskite with a proper bandgap of ≈1.7 eV becomes the most competitive candidate. However, its poor phase stability, hydrophobicity, and high‐density defects have limited the development of CsPbI₃ PSCs. To overcome these obstacles for achieving high‐performance CsPbI₃ PSCs, additive engineering has been widely used, which has rapidly promoted the power conversion efficiency (PCE) to over 19%. Herein, the progress of additive engineering in CsPbI₃ PSCs is systematically reviewed. First, the roles of additives in CsPbI₃ PSCs are introduced, including improving phase stability, increasing moisture resistance, and passivating defects. Then, the additive engineering is categorized (additive engineering in perovskites and at perovskite/hole transport layer interfaces) and reviewed in detail. Finally, future research directions on additive engineering are suggested for further enhancing stability and improving PCE.

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.

The recent progress of CsPbI₃ perovskite for highly efficient and stable photovoltaics is summarized. Furthermore, those important phase stabilization strategies for black‐phase CsPbI₃ are also discussed. With the advancing of fundamental studies on CsPbI₃ perovskite material properties, the CsPbI₃ perovskite and other inorganic perovskites will become more and more promising for high‐efficiency and stable perovskite solar cells.

Abstract

Research on chemically stable inorganic perovskites has achieved rapid progress in terms of high efficiency exceeding 19% and high thermal stabilities, making it one of the most promising candidates for thermodynamically stable and high‐efficiency perovskite solar cells. Among those inorganic perovskites, CsPbI₃ with good chemical components stability possesses the suitable bandgap (≈1.7 eV) for single‐junction and tandem solar cells. Comparing to the anisotropic organic cations, the isotropic cesium cation without hydrogen bond and cation orientation renders CsPbI₃ exhibit unique optoelectronic properties. However, the unideal tolerance factor of CsPbI₃ induces the challenges of different crystal phase competition and room temperature phase stability. Herein, the latest important developments regarding understanding of the crystal structure and phase of CsPbI₃ perovskite are presented. The development of various solution chemistry approaches for depositing high‐quality phase‐pure CsPbI₃ perovskite is summarized. Furthermore, some important phase stabilization strategies for black phase CsPbI₃ are discussed. The latest experimental and theoretical studies on the fundamental physical properties of photoactive phase CsPbI₃ have deepened the understanding of inorganic perovskites. The future development and research directions toward achieving highly stable CsPbI₃ materials will further advance inorganic perovskite for highly stable and efficient photovoltaics.

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 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.

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.

An interfacial layer of triphenylamine–polystyrene blend is used between the perovskite layer and charge‐transporting layer to concurrently suppress energy loss and improve device stability. The energy loss is reduced from 0.49 to 0.35 eV, along with a large open‐circuit voltage of 1.18 V and a high power conversion efficiency of 22.1% in air‐stable perovskite solar cells.

Energy loss induced by nonradiative recombinations plays a critical role in determining power conversion efficiencies in perovskite solar cells, whereas device stability impacts their long‐time reliability in the ambient environment. It is an important challenge to suppress energy loss and improve device stability simultaneously. Herein, an interfacial layer of triphenylamine (TPA):polystyrene (PS) blend coated on the hybrid perovskite layer to concurrently suppress energy loss and improve device stability is reported. The energy loss is suppressed from 0.49 to 0.35 eV by passivating surface defects in hybrid perovskites via Lewis acid–base interactions with the combination of electron‐donating aromatic nucleus in PS and tertiary amine in TPA, leading to perovskite solar cells with a high open‐circuit voltage of 1.18 V, a fill factor of about 80%, and a power conversion efficiency of 22.1%. Meanwhile, the device stability in the ambient environment is improved significantly by the TPA:PS blend due to its superior hydrophobicity which is suggested by its high contact angle of 91.1° as compared to 64.0° for the pristine perovskite film. Herein, an efficient interfacial engineering approach with the TPA:PS blend to suppress energy loss and improve device stability simultaneously towards realistic applications is demonstrated.

Further improvement and stabilization of perovskite solar cell (PSC) performance are essential to achieve the commercial viability of next-generation photovoltaics. Considering the benefits of fluorination to conjugated materials for energy levels, hydrophobicity, and noncovalent interactions, two fluorinated isomeric analogs of the well-known hole-transporting material (HTM) Spiro-OMeTAD are developed and used as HTMs in PSCs. The structure–property relationship induced by constitutional isomerism is investigated through experimental, atomistic, and theoretical analyses, and the fabricated PSCs feature high efficiency up to 24.82% (certified at 24.64% with 0.3-volt voltage loss), along with long-term stability in wet conditions without encapsulation (87% efficiency retention after 500 hours). We also achieve an efficiency of 22.31% in the large-area cell.

Herein, a one‐step solution‐processing of [MA_0.9Cs_0.1Pb(I_0.6Br_0.4)₃] wide‐bandgap perovskite using phenylhydrazine iodide with amino groups to successfully passivate the trap density within grain boundaries and increase the perovskite grain size is demonstrated. The reinforced morphology and grain boundaries treatment considerably enhance the power conversion efficiency from 12.16% for pristine to 14.63% for the treated devices.

Due to the attraction of fabricating highly efficient tandem solar cells, wide‐bandgap perovskite solar cells (PSCs) have attracted substantial interest in recent years. However, polycrystalline perovskite thin‐films show the existence of trap states at grain boundaries which diminish the optoelectronic properties of the perovskite and thus remains a challenge. Here, a one‐step solution‐processing of [ MA0.9Cs0.1Pb(I0.6Br0.4)3] wide‐bandgap perovskite using phenylhydrazine iodide with amino groups is demonstrated to successfully passivate the trap density within grain boundaries and increase the perovskite grain size. The reinforced morphology and grain boundaries treatment considerably enhanced the power conversion efficiency (PCE) from 12.16% for pristine to 14.63% for the treated devices. This strategy can be easily adopted to other perovskites and help realize highly efficient perovskite solar cells.

The commercially available pyridinedicarboxylic acid (PDA) molecule with one pyridine and two carboxylic acid groups is used as a passivating agent to cure the defects at both the surfaces and grain boundaries of MAPbI₃ perovskites. A champion power conversion efficiency (PCE) approaching 19% with optimized long‐term stability and thermal stability is achieved in PDA‐passivated perovskite solar cells (PSCs).

Electronic defects and grain boundaries of perovskite films will significantly deteriorate both the efficiency and the stability of perovskite solar cells (PSCs), and various methods aimed to reduce these defects are proposed. Herein, an organic solid molecule of pyridinedicarboxylic acid (PDA) with one pyridine and two carboxylic acid groups is used as a passivating agent to cure the defects by regulating the perovskite microstructures in a multiple manner. The defects located at both the surfaces and grain boundaries of polycrystalline MAPbI₃ perovskites are simultaneously passivated through the multiple coordination effects between the used functional groups and uncoordinated Pb²⁺, regardless of the substitution sites of the carboxylic acid and pyridine. Impressively, the PDA‐passivated inverted PSCs achieve remarkably enhanced power conversion efficiencies (PCEs) from 16.43% to nearly 19% and maintain over 90% of its original PCE after 1300 h under an inert environment. These findings indicate that the commercially available PDA molecule emerges as an efficient passivating agent of perovskite defects capable of stimulating the combined effects of the multiple functional groups, which is highly promising for the practical applications of PSCs with both high efficiency and good stability.

An inorganic CsPbI₂Br perovskite solar cell employing organic ligands armored ZnO as the electron transport materials achieves a maximum power conversion efficiency of 16.84%, with superior photo‐ and thermal‐ stabilities.

Abstract

Inorganic perovskite solar cells (PSCs) have witnessed great progress in recent years due to their superior thermal stability. As a representative, CsPbI₂Br is attracting considerable attention as it can balance the high efficiency of CsPbI₃ and the stability of CsPbBr₃. However, most research employs doped charge transport materials or applies bilayer transport layers to obtain decent performance, which vastly complicates the fabrication process and scarcely satisfies the commercial production requirement. In this work, all‐layer‐doping‐free inorganic CsPbI₂Br PSCs using organic ligands armored ZnO as the electron transport materials achieve an encouraging performance of 16.84%, which is one of the highest efficiencies among published works. Meanwhile, both the ZnO‐based CsPbI₂Br film and device show superior photostability under continuous white light‐emitting diode illumination and improved thermal stability under 85 °C. The remarkable enhanced performance arises from the favorable organic ligands (acetate ions) residue in the ZnO film, which not only can conduce to maintain high crystallinity of perovskite, but also passivate traps at the interface through cesium/acetate interactions, thus suppressing the photo‐ and thermal‐ induced perovskite degradation.

Nature Nanotechnology, Published online: 21 September 2020; doi:10.1038/s41565-020-0765-7

Annealing‐free solution‐processable aqueous MoO _x are developed and applied in bulk‐heterojunction polymer solar cells based on non‐fullerene system PBDB‐T‐2F:Y6. The solar cells with aqueous MoO _x exhibit higher efficiencies and better stabilities without high‐temperature annealing compared to the solar cells with PEDOT:PSS.

Abstract

A charge transport layer based on transition metal‐oxides prepared by an anhydrous sol–gel method normally requires high‐temperature annealing to achieve the desired quality. Although annealing is not a difficult process in the laboratory, it is definitely not a simple process in mass production, such as roll‐to‐roll, because of the inevitable long cooling step that follows. Therefore, the development of an annealing‐free solution‐processable metal‐oxide is essential for the large‐scale commercialization. In this work, a room‐temperature processable annealing‐free “aqueous” MoO _x solution is developed and applied in non‐fullerene PBDB‐T‐2F:Y6 solar cells. By adjusting the concentration of water in the sol–gel route, an annealing‐free MoO _x with excellent electrical properties is successfully developed. The PBDB‐T‐2F:Y6 solar cell with the general MoO _x prepared by the anhydrous sol–gel method shows a low efficiency of 7.7% without annealing. If this anhydrous MoO _x is annealed at 200 °C, the efficiency is recovered to 17.1%, which is a normal value typically observed in conventional structure PBDB‐T‐2F:Y6 solar cells. However, without any annealing process, the solar cell with aqueous MoO _x exhibits comparable performance of 17.0%. In addition, the solar cell with annealing‐free aqueous MoO _x exhibits better performance and stability without high‐temperature annealing compared to the solar cells with PEDOT:PSS.

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.

Annealing‐free solution‐processable aqueous MoO _x are developed and applied in bulk‐heterojunction polymer solar cells based on non‐fullerene system PBDB‐T‐2F:Y6. The solar cells with aqueous MoO _x exhibit higher efficiencies and better stabilities without high‐temperature annealing compared to the solar cells with PEDOT:PSS.

Abstract

A charge transport layer based on transition metal‐oxides prepared by an anhydrous sol–gel method normally requires high‐temperature annealing to achieve the desired quality. Although annealing is not a difficult process in the laboratory, it is definitely not a simple process in mass production, such as roll‐to‐roll, because of the inevitable long cooling step that follows. Therefore, the development of an annealing‐free solution‐processable metal‐oxide is essential for the large‐scale commercialization. In this work, a room‐temperature processable annealing‐free “aqueous” MoO _x solution is developed and applied in non‐fullerene PBDB‐T‐2F:Y6 solar cells. By adjusting the concentration of water in the sol–gel route, an annealing‐free MoO _x with excellent electrical properties is successfully developed. The PBDB‐T‐2F:Y6 solar cell with the general MoO _x prepared by the anhydrous sol–gel method shows a low efficiency of 7.7% without annealing. If this anhydrous MoO _x is annealed at 200 °C, the efficiency is recovered to 17.1%, which is a normal value typically observed in conventional structure PBDB‐T‐2F:Y6 solar cells. However, without any annealing process, the solar cell with aqueous MoO _x exhibits comparable performance of 17.0%. In addition, the solar cell with annealing‐free aqueous MoO _x exhibits better performance and stability without high‐temperature annealing compared to the solar cells with PEDOT:PSS.

A series of copolymers via a random copolymerization approach are designed and synthesized. The well‐defined fibril interpenetrating morphology with appropriate phase separation in PT2‐based blends can efficiently suppress the unfavorable aggregation, resulting in excellent morphological stability and high efficiency. The work demonstrates the importance of optimization of fibril network morphology in realizing high‐efficiency and ambient‐stable polymer solar cells.

Abstract

Morphological stability is crucially important for the long‐term stability of polymer solar cells (PSCs). Many high‐efficiency PSCs suffer from metastable morphology, resulting in severe device degradation. Here, a series of copolymers is developed by manipulating the content of chlorinated benzodithiophene‐4,8‐dione (T1‐Cl) via a random copolymerization approach. It is found that all the copolymers can self‐assemble into a fibril nanostructure in films. By altering the T1‐Cl content, the polymer crystallinity and fibril width can be effectively controlled. When blended with several nonfullerene acceptors, such as TTPTT‐4F, O‐INIC3, EH‐INIC3, and Y6, the optimized fibril interpenetrating morphology can not only favor charge transport, but also inhibit the unfavorable molecular diffusion and aggregation in active layers, leading to excellent morphological stability. The work demonstrates the importance of optimization of fibril network morphology in realizing high‐efficiency and ambient‐stable PSCs, and also provides new insights into the effect of chemical structure on the fibril network morphology and photovoltaic performance of PSCs.

The recent progress of CsPbI₃ perovskite for highly efficient and stable photovoltaics is summarized. Furthermore, those important phase stabilization strategies for black‐phase CsPbI₃ are also discussed. With the advancing of fundamental studies on CsPbI₃ perovskite material properties, the CsPbI₃ perovskite and other inorganic perovskites will become more and more promising for high‐efficiency and stable perovskite solar cells.

Abstract

Research on chemically stable inorganic perovskites has achieved rapid progress in terms of high efficiency exceeding 19% and high thermal stabilities, making it one of the most promising candidates for thermodynamically stable and high‐efficiency perovskite solar cells. Among those inorganic perovskites, CsPbI₃ with good chemical components stability possesses the suitable bandgap (≈1.7 eV) for single‐junction and tandem solar cells. Comparing to the anisotropic organic cations, the isotropic cesium cation without hydrogen bond and cation orientation renders CsPbI₃ exhibit unique optoelectronic properties. However, the unideal tolerance factor of CsPbI₃ induces the challenges of different crystal phase competition and room temperature phase stability. Herein, the latest important developments regarding understanding of the crystal structure and phase of CsPbI₃ perovskite are presented. The development of various solution chemistry approaches for depositing high‐quality phase‐pure CsPbI₃ perovskite is summarized. Furthermore, some important phase stabilization strategies for black phase CsPbI₃ are discussed. The latest experimental and theoretical studies on the fundamental physical properties of photoactive phase CsPbI₃ have deepened the understanding of inorganic perovskites. The future development and research directions toward achieving highly stable CsPbI₃ materials will further advance inorganic perovskite for highly stable and efficient photovoltaics.

The T2‐CNORH organic passivation layer (OPL) is used to obtain low energy loss organic photovoltaics. The T2‐CNORH‐deposited PM6:Y6 device exhibits a power conversion efficiency (PCE) of 15.5% with low non‐radiative energy loss (0.203 eV). Furthermore, the OPL improves various photoactive layer systems with a best PCE of 16.4% for the PM6:Y7 system.

Abstract

Despite the tremendous development of various high‐performing photoactive layers in organic photovoltaic (OPVs) cells, improving their performance remains the most important challenge in the field. Here, an effective and compatible strategy (i.e., the concept of vacuum deposition of an organic passivation layer (OPL) on the photoactive layer) is presented to enhance the efficiency of the state‐of‐the‐art photoactive systems, where easy‐deposition processable T2‐ORH and T2‐CNORH OPLs are used. After the deposition process, T2‐ORH forms 2D‐like edge‐on crystalline structure, and the 3D‐like face‐on crystalline growth is induced in T2‐CNORH. Resulting from its relatively higher crystalline features and increased wettability with the cathode interfacial material, the performance of T2‐CNORH‐deposited OPVs with both small and the scaled‐up areas surpass devices without OPL and with T2‐ORH. Experimental studies are conducted linking conductivity, electroluminescence quantum efficiency, carrier transport, and recombination dynamics to find the reasons for the performance difference. Furthermore, by applying the T2‐CNORH to other photoactive platforms, the efficiencies are enhanced by 4.4–9.0% relative to those of the corresponding control devices; an optimal 16.4% efficiency is achieved, which validates its great applicability for photoactive layers that will be developed in the near future.

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.

Annealing‐free solution‐processable aqueous MoO _x are developed and applied in bulk‐heterojunction polymer solar cells based on non‐fullerene system PBDB‐T‐2F:Y6. The solar cells with aqueous MoO _x exhibit higher efficiencies and better stabilities without high‐temperature annealing compared to the solar cells with PEDOT:PSS.

Abstract

A charge transport layer based on transition metal‐oxides prepared by an anhydrous sol–gel method normally requires high‐temperature annealing to achieve the desired quality. Although annealing is not a difficult process in the laboratory, it is definitely not a simple process in mass production, such as roll‐to‐roll, because of the inevitable long cooling step that follows. Therefore, the development of an annealing‐free solution‐processable metal‐oxide is essential for the large‐scale commercialization. In this work, a room‐temperature processable annealing‐free “aqueous” MoO _x solution is developed and applied in non‐fullerene PBDB‐T‐2F:Y6 solar cells. By adjusting the concentration of water in the sol–gel route, an annealing‐free MoO _x with excellent electrical properties is successfully developed. The PBDB‐T‐2F:Y6 solar cell with the general MoO _x prepared by the anhydrous sol–gel method shows a low efficiency of 7.7% without annealing. If this anhydrous MoO _x is annealed at 200 °C, the efficiency is recovered to 17.1%, which is a normal value typically observed in conventional structure PBDB‐T‐2F:Y6 solar cells. However, without any annealing process, the solar cell with aqueous MoO _x exhibits comparable performance of 17.0%. In addition, the solar cell with annealing‐free aqueous MoO _x exhibits better performance and stability without high‐temperature annealing compared to the solar cells with PEDOT:PSS.