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An efficient photon downshifting layer is developed based on ultrasonic spray deposition of a platinum(II) complex, and considerable improvements in both the performance and stability of perovskite solar cells are observed. The photon downshifting layer is demonstrated to be applicable to various types of perovskite solar cells, achieving a maximum device performance of 22.0%.

Abstract

Despite a rapid increase in light harvesting efficiencies, organic–inorganic hybrid perovskite solar cells (PSCs) exhibit relatively inefficient photocurrent generation in the UV region and severe degradation when exposed to UV light and humidity. Herein, to enhance UV and humidity stability as well as photocurrent generating efficiency, a water‐repellent platinum(II) complex, Pt‐F, is developed as a luminescent photon downshifting layer (PDL) for PSCs. The Pt‐F PDL is fabricated on the glass substrate of a PSC using ultrasonic spray deposition, resulting in a considerably higher crystallinity and photoluminescence quantum yield (PLQY) than those fabricated by conventional spin‐coating processes (PLQYs of 77% and 19%, respectively). A maximum device performance of 22.0% is achieved through the addition of a PDL coating to a 21.4% efficient PSC owing to the long‐range photon downshifting effect of Pt‐F, as confirmed by the enhanced spectral response of the device in the UV region. Moreover, remarkable improvements in UV and humidity stability are observed in Pt‐F‐coated PSCs. The versatile effects of the Pt‐F‐based PDL, when fabricated by ultrasonic spray deposition, suggest wide ranging applicability that can improve the performance and stability of other optoelectronic devices.

Three homologous small molecule donors with hydrogen, fluorine, and chlorine substitution afford organic solar cells with efficiencies over 10% in combination with a common acceptor. The chlorinated derivative exhibits a more crystalline nanomorphology with relatively pure domains and provides more than 12% efficiency.

Abstract

Compared to conjugated polymers, small‐molecule organic semiconductors present negligible batch‐to‐batch variations, but presently provide comparatively low power conversion efficiencies (PCEs) in small‐molecular organic solar cells (SM‐OSCs), mainly due to suboptimal nanomorphology. Achieving precise control of the nanomorphology remains challenging. Here, two new small‐molecular donors H13 and H14, created by fluorine and chlorine substitution of the original donor molecule H11, are presented that exhibit a similar or higher degree of crystallinity/aggregation and improved open‐circuit voltage with IDIC‐4F as acceptor. Due to kinetic and thermodynamic reasons, H13‐based blend films possess relatively unfavorable molecular packing and morphology. In contrast, annealed H14‐based blends exhibit favorable characteristics, i.e., the highest degree of aggregation with the smallest paracrystalline π–π distortions and a nanomorphology with relatively pure domains, all of which enable generating and collecting charges more efficiently. As a result, blends with H13 give a similar PCE (10.3%) as those made with H11 (10.4%), while annealed H14‐based SM‐OSCs have a significantly higher PCE (12.1%). Presently this represents the highest efficiency for SM‐OSCs using IDIC‐4F as acceptor. The results demonstrate that precise control of phase separation can be achieved by fine‐tuning the molecular structure and film formation conditions, improving PCE and providing guidance for morphology design.

Water is added into the precursor solution to assist crystal growths of quasi‐2D perovskite films featuring ordered phase distribution and favored crystal orientation. A champion efficiency of 18.04% is realized in (BA)₂(MA_0.8FA_0.15Cs_0.05)₄Pb₅I₁₆‐based quasi‐2D perovskite solar cells.

Abstract

Organic–inorganic hybrid quasi‐2D perovskites have shown excellent stability for perovskite solar cells (PSCs), while the poor charge transport in quasi‐2D perovskites significantly undermines their power conversion efficiency (PCE). Here, studies on water‐controlled crystal growth of quasi‐2D perovskites are presented to achieve high‐efficiency solar cells. It is demonstrated that the (BA)₂MA₄Pb₅I₁₆‐based PSCs (n = 5) processed with water‐containing precursors display an increased short‐circuit current density (J _sc) of 19.01 mA cm⁻² and PCE over 15%. The enhanced performance is attributed to synergetic growths of the 3D and 2D phase components aided by the formed hydration (MAI∙H₂O), leading to modulations on the crystal orientation and phase distribution of various n‐value components, which facilitate interphase charge transfer and charge sweepout throughout the device. The water‐assisted crystallization is further applied to triple cation‐based (BA)₂(MA_0.8FA_0.15Cs_0.05)₄Pb₅I₁₆ quasi‐2D perovskites, which generate a remarkable PCE of 18.04%. Despite the presence of water in the precursors, the devices exhibit a satisfactory thermal stability with the PCE degradation <15% under continuous thermal aging at 60 °C for over 500 h.

Highly efficient temperature‐dependent‐aggregation polymer‐based organic solar cells are fabricated by hot slot‐die coating with hydrocarbon solvents. Power conversion efficiencies of 15.2%, 15.4%, and 15.6% are obtained when chlorobenzene, 1,2,4‐trimethylbenzene (TMB), and ortho‐xylene are used, respectively.

Abstract

Organic solar cells (OSCs) have made rapid progress in terms of their development as a sustainable energy source. However, record‐breaking devices have not shown compatibility with large‐scale production via solution processing in particular due to the use of halogenated environment‐threatening solvents. Here, slot‐die fabrication with processing involving hydrocarbon‐based solvents is used to realize highly efficient and environmentally friendly OSCs. Highly compatible slot‐die coating with roll‐to‐roll processing using halogenated (chlorobenzene (CB)) and hydrocarbon solvents (1,2,4‐trimethylbenzene (TMB) and ortho‐xylene (o‐XY)) is used to fabricate photoactive films. Controlled solution and substrate temperatures enable similar aggregation states in the solution and similar kinetics processes during film formation. The optimized blend film nanostructures for different solvents in the highly efficient PM6:Y6 blend is adopted to show a similar morphology, which results in device efficiencies of 15.2%, 15.4%, and 15.6% for CB, TMB, and o‐XY solvents. This approach is successfully extended to other donor–acceptor combinations to demonstrate the excellent universality of this method. The results combine a method to optimize the aggregation state and film formation kinetics with the fabrication of OSCs with environmentally friendly solvents by slot‐die coating, which is a critical finding for the future development of OSCs in terms of their scalable production and high‐performance.

Publication date: Available online 12 August 2020

Source: Nano Energy

Author(s): George Syrrokostas, Alexandros Dokouzis, Spyros N. Yannopoulos, George Leftheriotis

Publication date: December 2020

Source: Nano Energy, Volume 78

Author(s): Qing Ma, Zhenrong Jia, Lei Meng, Jinyuan Zhang, Huotian Zhang, Wenchao Huang, Jun Yuan, Feng Gao, Yan Wan, Zhanjun Zhang, Yongfang Li

2D perovskites are of great importance to increase both the efficiency and stability of perovskite interfaces. Motivated by the stronger halogen bond interaction, (5FBzAI)₂PbI₄ used as a capping layer in 3D/2D systems self‐organizes with an in‐plane crystal orientation, inducing a reproducible increase of ≈60 mV in the V _oc, and remarkable operational stability.

Abstract

Despite organic/inorganic lead halide perovskite solar cells becoming one of the most promising next‐generation photovoltaic materials, instability under heat and light soaking remains unsolved. In this work, a highly hydrophobic cation, perfluorobenzylammonium iodide (5FBzAI), is designed and a 2D perovskite with reinforced intermolecular interactions is engineered, providing improved passivation at the interface that reduces charge recombination and enhances cell stability compared with benchmark 2D systems. Motivated by the strong halogen bond interaction, (5FBzAI)₂PbI₄ used as a capping layer aligns in in‐plane crystal orientation, inducing a reproducible increase of ≈60 mV in the V _oc, a twofold improvement compared with its analogous monofluorinated phenylethylammonium iodide (PEAI) recently reported. This endows the system with high power conversion efficiency of 21.65% and extended operational stability after 1100 h of continuous illumination, outlining directions for future work.

This Minireview describes developments in all‐polymer solar cells containing a new type of n‐type conjugated polymer, polymerized small‐molecule acceptors (PSMAs). PSMAs combine the merits of small‐molecule acceptors (narrow band gap, strong absorption, and suitable electronic energy levels) with the good film formation, higher morphology and light‐irradiation stability of polymers.

Abstract

All‐polymer solar cells (all‐PSCs) have drawn tremendous research interest in recent years, due to their inherent advantages of good film formation, stable morphology, and mechanical flexibility. The most representative and most widely used n‐CP acceptor was the naphthalene diimide based D‐A copolymer N2200 before 2017, and the power conversion efficiency (PCE) of the all‐PSCs based on N2200 reached over 8% in 2016. However, the low absorption coefficient of N2200 in the near‐infrared (NIR) region limits the further increase of its PCE. In 2017, we proposed a strategy of polymerizing small‐molecule acceptors (SMAs) to construct new‐generation polymer acceptors. The polymerized SMAs (PSMAs) possess low band gap and strong absorption in the NIR region, which attracted great attention and drove the PCE of the all‐PSCs to over 15% recently. In this Minireview we explain the design strategies of the molecular structure of PSMAs and describe recent research progress. Finally, current challenges and future prospects of the PSMAs are analyzed and discussed.

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.

CsSn_0.6Ge_0.4I₃ nanocrystals have been synthesized for the first time by a B‐site co‐alloying strategy. The introduction of Ge effectively decreases the high density of intrinsic Sn defects, resulting in an extended excitonic lifetime and enhanced solar cell performance. The stability of the new nanocrystals also improves owing to the effective protection of Sn²⁺ against oxidation.

Abstract

Colloidal lead‐free perovskite nanocrystals have recently received extensive attention because of their facile synthesis, the outstanding size‐tunable optoelectronic properties, and less or no toxicity in their commercial applications. Tin (Sn) has so far led to the most efficient lead‐free solar cells, yet showing highly unstable characteristics in ambient conditions. Here, we propose the synthesis of all‐inorganic mixture Sn‐Ge perovskite nanocrystals, demonstrating the role of Ge²⁺ in stabilizing Sn²⁺ cation while enhancing the optical and photophysical properties. The partial replacement of Sn atoms by Ge atoms in the nanostructures effectively fills the high density of Sn vacancies, reducing the surface traps and leading to a longer excitonic lifetime and increased photoluminescence quantum yield. The resultant Sn‐Ge nanocrystals‐based devices show the highest efficiency of 4.9 %, enhanced by nearly 60 % compared to that of pure Sn nanocrystals‐based devices.

A large‐grained CsPbBr₃ perovskite film with improved energy‐level alignment and hole mobility is fabricated by compositional engineering of Cl ion doping, which suppresses charge recombination thus affording a champion power conversion efficiency (PCE) as high as 9.73% for carbon‐based all‐inorganic CsPbBr_2.98Cl_0.02 PSC free of encapsulation with excellent operational stability.

Carbon‐based CsPbBr₃ perovskite solar cells (PSCs) without hole‐transporting layers (HTLs) have aroused extensive attention due to their low manufacturing cost and prominent ambient stability. However, the defects of perovskite film and the poor charge extraction within PSCs result in severe charge recombination, which restricts the further enhancement of device efficiency. In view of this critical point, a compositional engineering of CsPbBr₃ perovskite via doping with Cl⁻ ions is presented herein to decrease the trap states and enhance the charge extraction. It is revealed that the doping of Cl⁻ ions not only enlarges the grain size and thereby reduces the trap‐state density, but also optimizes the energy‐level alignment and improves the hole mobility of the perovskite film, leading to an evidently suppressed charge recombination and improved charge extraction and transportation. As a result, a champion power conversion efficiency (PCE) of 9.73% is achieved for carbon‐based HTL‐free CsPbBr_2.98Cl_0.02 PSC, yielding a marked enhancement in comparison with 6.69% efficiency for the control. Meanwhile, the thermal and moisture stabilities of unencapsulated CsPbBr_2.98Cl_0.02 PSC are improved, maintaining 93% and 95% of the initial PCE after expose to air atmosphere with 80% relative humidity (RH) and at 80 °C over 60 days, respectively.

Studies on effect of additives of FAX (X = Cl, Br, and I, FA = formamidinium) and ACl (A = MA, Cs, Rb, and NH₄) in FAPbI₃‐based perovskite solar cells reveal that the FACl additive shows best performance over other additives due to passivating the grain boundary effectively without altering bandgap of pristine perovskite.

Herein, the dependence of photovoltaic performance on the additives of FAX (X = Cl, Br, and I, FA = formamidinium) and ACl [A = methylammonium (MA), Cs, Rb, and NH₄] in FAPbI₃‐based perovskite solar cells (PSCs) is reported. Effect of concentration on photovoltaic parameters is first screened for each additive, from which optimal concentration is determined with respect to the pristine without additive. Power conversion efficiency (PCE) is significantly improved from 16.55% to 22.51% after adding 20 mol% FACl in the perovskite precursor solution, whereas moderate increase in PCE to 20.08% and 19.97% is observed for FABr and FAI, respectively, indicating an important role of chloride. MACl and CsCl improved PCE to 20.81% and 20.59%, respectively, which is, however, inferior to FACl. A significantly increased carrier lifetime by treating FACl is responsible for the best performance. Energy dispersive X‐ray spectroscopy shows that chloride in the additive FACl is not incorporated in grain but placed on the grain boundary, which plays an important role in passivating iodide‐deficient grain boundary. The FACl additive has benefits over other additives because it cannot change the bandgap of FAPbI₃.

A methylammonium chloride (MACl) additive is used to synthesize FA_1–x MA _x PbI₃ films. The best molar fraction of this additive is determined. The MA content in thin films actually used in solar cells is x = 0.06. This amount is thermodynamically the best for the stabilization of this highly efficient perovskite. The perovskite solar cell achieves a stabilized power conversion efficiency as high as 22.06%.

Nowadays, complex chemistry and precursor solution compositions are developed to stabilize hybrid perovskite films and boost the efficiency of perovskite solar cells (PSCs). In this context, determining the actual composition of these layers, especially in organic cations, and understanding the chemistry behind is challenging. Herein, the introduction of methylammonium (MA⁺) in formamidinium lead iodide (FAPbI₃) 3D perovskite is considered to stabilize the α‐phase, whose quantity must be minimized to reduce the material hydrophilicity and its possible destabilization by degassing. The key effects of methylammonium chloride (MACl) additive on the growth of FA_1–x MA _x PbI₃ perovskite layers are studied. Liquid nuclear magnetic resonance (NMR) is used to analyze the photovoltaic layers. NMR peaks and their origin are identified. The MA and FA content in films actually used in PSCs is reliably measured and prepared over a large additive molar concentration ratio. x is quantified at 0.06 ± 0.01 for pure films, which corresponds to the best entropic compound stabilization. It results in PSCs with a stabilized power conversion efficiency as high as 22.06%. These PSCs are shown to be highly stable under solar irradiation and high moisture.

A novel bifacial passivation strategy which simultaneously suppresses trap states within TiO₂ and perovskite through interaction between functional groups and defects is demonstrated for printable mesoscopic PSCs. The passivation treatment to TiO₂ surface not only reduces the energy barrier between TiO₂ and perovskite for accelerating the charge transfer but also passivates the uncoordinated Pb defects on the perovskite interface.

Surface defects, which mediate nonradiative recombination, are detrimental to both the photovoltaic performance and stability of perovskite solar cells (PSCs). Improving photovoltage and fill factor (FF) in screen‐printed mesoporous PSCs is a major challenge for approaching the power conversion efficiency (PCE) of the planar configured devices. Herein, a novel bifacial passivation strategy which simultaneously suppresses deep trap states within TiO₂ and perovskite through interaction between functional groups and defects is demonstrated for fully printable mesoscopic PSCs. The application of monoethanolamine (MEA) treatment to TiO₂ surface not only reduces the energy barrier between TiO₂ and perovskite for accelerating the charge transfer but also passivates the uncoordinated Pb defects on the perovskite interface. Due to the synergistic effect of charge extraction promotion and trap passivation, the fabricated PSCs deliver a champion PCE of 15.5% with an enhanced V _oc of 0.94 V and FF of 70.4% compared with PSCs without MEA passivation, and the device maintains 97% of its topmost PCE after 240 h under constant simulated solar illumination in air atmosphere. This investigation helps exploit new approaches for defect passivation to further improve both the efficiency and stability of printable mesoscopic PSCs.

A fibril network strategy is demonstrated to fabricate high‐efficiency thick‐film organic solar cells (OSCs). The fibril network morphology provides effective hole transport channel and the incorporation of high crystalline nonfullerene acceptor ensures high electron transport in a thick film. As a result, the OSCs show high efficiencies to ≈12% with wide toleration of active layer thickness.

Industrial printing production of organic solar cells (OSCs) requires high power conversion efficiency (PCE) with wide toleration of active layer thickness. Herein, high‐efficiency thick‐film OSCs are demonstrated using a polymer fibril network strategy (FNS), which involves a donor polymer (PT2) that can self‐assemble into fibril nanostructure, and two nonfullerene acceptors with different crystalline properties. The fibril network can form a high‐speed hole transport channel and the addition of IDIC as a third component in active layers can improve the electron transport. As a result, the OSCs show high PCEs of ≈12% with wide toleration of active layer thickness (from 100 to 500 nm). The results indicate that FNS is a promising approach for the fabrication of highly efficient thick‐film PSCs, which can facilitate the commercialization of OSCs.

The A‐D‐A′‐D‐A strategy is applied to develop two new Y6‐type unfused‐ring acceptors. The resulting fluorinated unfused acceptors lock more planar conformation, thus exhibiting red‐shifted absorption and better aggregation properties, leading to high device efficiencies of over 12%.

Unfused‐ring acceptors (UFAs) have gained considerable research attention as they offer simple chemical structures through simplified synthesis methods, which would boost the commercialization of organic solar cells (OSCs). Recently, a new small molecule acceptor (SMA) named Y6 was reported, yielding high‐performance OSCs. Herein, the Y6‐like A‐DA′D‐A framework is developed to A‐D‐A′‐D‐A‐type backbone adopted in constructing UFAs. Two new Y6‐like UFAs are synthesized within four steps and the effect of noncovalent atoms at the central electron‐deficient core on material properties and device performances is studied. It is found that the introduction of fluorine atoms can bring larger red‐shift in the absorption spectra and better aggregation of the resulting UFA film states compared with those of oxygen atoms. Interestingly, the variations in the noncovalent interaction atoms induce different intermolecular charge transfer between donors and UFAs. When blended with another economical donor, PTQ10, F substitution at the benzothiadiazole ring is more effective than O substitution, leading to the increased short‐circuit current density (J _SC) and higher efficiency of over 12%, among the best performances of UFA‐based OSCs. This contribution demonstrates the appropriate introduction of noncovalent interaction is a promising method for tuning energy levels, absorption, and aggregation of UFAs for high‐performance OSCs.

A new side chain engineering strategy is developed to rationally adjust the crystallinity of small molecule acceptors. Through restricting the rotation of bulky side chain on carbazole‐based acceptor, the crystallinity and morphology of the heterojunction are optimized, leading to a high power conversion efficiency of 12.06%.

Herein, three carbazole‐based small molecule acceptors (SMAs), named 4TC‐4F‐C8C8, 4TC‐4F‐C6C8, and 4TC‐4F‐C16, are synthesized to study the influence of side chain conformation on SMAs. The three acceptors exhibit similar optical and electrochemical properties, but different crystallization properties. 4TC‐4F‐C16 shows a high crystallinity due to the small steric hindrance of linear n‐hexadecyl (C16) side chain. The large steric hindrance and free rotation for the 2‐hexydecyl (C6C8) side chain seriously disturb the molecular packing and result in a low crystallinity for 4TC‐4F‐C6C8. Despite the large steric hindrance for the 1‐octylnonyl (C8C8) side chain, 4TC‐4F‐C8C8 shows a moderate crystallinity due to the large torsion barrier restricting the rotation of C8C8 side chain. Attributing to the ideal morphology and better crystalline ordering in blend film, organic solar cell based on poly[4,8‐bis(5‐(2‐ethylhexyl)thiophen‐2‐yl)benzo[1,2‐b:4,5‐b′]‐dithiophene‐alt‐N‐(2‐hexyldecyl)‐5′5‐bis[3‐(decylthio)thiophene‐2‐yl]‐2′2‐bithiophene‐3′3‐dicarboximide] (PBTIBDTT):4TC‐4F‐C8C8 displays a power conversion efficiency of 12.06%, higher than PBTIBDTT:4TC‐4F‐C6C8 (2.38%)‐ and PBTIBDTT:4TC‐4F‐C16 (9.53%)‐based devices. The work indicates that controlling the conformation of bulky side chain can tune the molecular packing of SMAs and the morphology of blend film, providing a new insight into the molecular design of SMAs.

The non‐fullerene acceptor small molecule (5Z,5′Z)‐5,5′‐((7,7′‐(9,9‐dioctyl‐9H‐fluorene‐2,7‐diyl)bis(benzo[c]1,2,5]thiadiazole‐7,4‐diyl))‐bis(methanylyl‐idene))bis(3‐ethyl‐2‐thioxothiazolidin‐4‐one) (FBR) is blended with the poly[(2,6‐(4,8‐bis(5‐(2‐ethylhexyl)thiophen‐2‐yl)benzo[1,2‐b:4,5‐b′]‐dithiophene)‐co‐(1,3‐di(5‐thiophen‐2‐yl)‐5,7‐bis(2‐ethylhexyl)benzo[1′,2′‐c:4,5‐c′]dithiophene‐4,8‐dione))] (PBDB‐T): 3,9‐bis(2‐methylene‐(3‐(1,1‐dicyanomethylene)‐indanone))‐5,5,11,11‐tetrakis(4‐hexylphenyl)‐dithieno[2,3‐d:2′,3′‐d′]‐s‐indaceno[1,2‐b:5,6‐b′]dithiophene) (ITIC) binary system to form the ITIC:FBR alloys, which simultaneously improves the performance and stability of solar cells.

Nanoscale morphology of the active layer plays a crucial role in the power conversion efficiency (PCE) and stability of polymer solar cells (PSCs). Blending the photoactive layer with a third component to produce a ternary system is considered a reliable approach to tune the nanomorphology, thereby improving the device performance. Herein, poly[(2,6‐(4,8‐bis(5‐(2‐ethylhexyl)thiophen‐2‐yl)benzo[1,2‐b:4,5‐b′]‐dithiophene)‐co‐(1,3‐di(5‐thiophen‐2‐yl)‐5,7‐bis(2‐ethylhexyl)benzo[1′,2′‐c:4,5‐c′]dithiophene‐4,8‐dione))] (PBDB‐T): 3,9‐bis(2‐methylene‐(3‐(1,1‐dicyanomethylene)‐indanone))‐5,5,11,11‐tetrakis(4‐hexylphenyl)‐dithieno[2,3‐d:2′,3′‐d′]‐s‐indaceno[1,2‐b:5,6‐b′]dithiophene) (ITIC) solar cells doped with a third small molecule are systematically investigated, namely, (5Z,5′Z)‐5,5′‐((7,7′‐(9,9‐dioctyl‐9H‐fluorene‐2,7‐diyl)bis(benzo[c]1,2,5]thiadiazole‐7,4‐diyl))‐bis(methanylyl‐idene))bis(3‐ethyl‐2‐thioxothiazolidin‐4‐one) (FBR). Owing to the wide optical bandgap of FBR, blending PBDB‐T:ITIC with FBR increases the device's light‐harvesting capability in the short wavelength range (400–550 nm), which improves the short circuit current. Differential scanning calorimetry and grazing incidence wide angle X‐ray scattering analyses reveal that the FBR exhibits impressive miscibility with ITIC, leading to the formation of ITIC:FBR alloys. Optimum performance is achieved with a PBDB‐T:ITIC:FBR (1:0.8:0.2) cell, which yields a PCE of 11.17%, demonstrating a 10% improvement relative to the PBDB‐T:ITIC binary cell. Crucially, the ternary solar cells also show improved device stability, which is attributed to the formation of ITIC:FBR alloys suppressing the crystallization of ITIC. This study provides deep insights into the performance‐ and stability‐related improvements available to PSCs devices that incorporate a third conjugated small molecule.

A full defects passivation strategy for superior carrier dynamics is demonstrated, which enables highly efficient perovskite solar cells operating in air.

Abstract

The lattice defects in the bulk and on the surface of the halide perovskite layer serve as trap sites and recombination centers to annihilate photogenerated carriers, determining the performance and stability of perovskite optoelectronic devices. Herein, the previously reported surface defects passivation engineering is extended to a full defects passivation strategy through stereoscopically introducing the cysteamine hydrochloride (CSA‐Cl) in the bulk and on the surface of perovskites. First‐principle density functional theory (DFT) calculations are employed to theoretically verify the multiple defects passivation effect of the CAS‐Cl on the perovskite. The perovskite layer with full defects passivation exhibits superior carrier dynamics as revealed by femtosecond transient absorption due to the reduced defect density determined by a highly sensitive photothermal deflection spectroscopy technique. Consequently, a high efficiency approaching 21% is achieved for the inverted planar perovskite solar cells (PVSCs). More importantly, the CAS‐Cl passivated PVSCs exhibit operation in air, which will be beneficial for the in situ device test for understanding the photophysics involved. This work provides a promising strategy to reduce the defects in both the perovskite bulk and surface for superior optoelectronic properties, facilitating the development of highly efficient and stable PVSCs and other optoelectronic devices.

The hybrid perovskite MAPbBr₃ is shown, for the first time, to incorporate the amino acid lysine. This incorporation is accompanied with a contraction of the host's unit cell, along with changes in its bandgap, phase transition temperature, and thermal expansion coefficient. Lysine serves as a molecular bridge and greatly increases the stability of the perovskite under humid conditions.

Abstract

Hybrid perovskites demonstrate high potential in optoelectronic applications. Their main drawback is their low stability under humid conditions. In this paper, one of nature's strategies is implemented—the incorporation of amino acids into the crystal lattice—in order to improve the stability of methylammonium lead bromide (MAPbBr₃) in water, and to tune its structure, as well as its optical and thermal properties. The amino acid lysine, which possesses two NH₃ ⁺ groups, is incorporated into the hybrid unit cell, by substituting two methylammonium ions and serves as a “molecular bridge”. This incorporation induces a decrease in the lattice parameter of the host, accompanied with an increase in its bandgap and noticeable changes in its morphology. Furthermore, a substantial decrease in the thermal expansion coefficient of MAPbBr₃ and a shift of its cubic‐to‐tetragonal phase transformation temperature are observed. Two different modes of incorporation are identified, which depend on the conditions of crystallization. These modes dictate the level of lysine incorporation and the magnitude of MAPbBr₃ bandgap changes. Notably, lysine incorporation strongly increases the perovskite stability in water. This study demonstrates a unique and promising approach to tune the properties and improve the stability of hybrid perovskites via this novel bioinspired route.

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%.

An aqueous‐solution‐processed cathode interlayer based on cost‐effective organosilica nanodots (OSiNDs) is demonstrated for organic solar cells (OSCs) with power conversion efficiency over 17% and excellent operational stability. The high photostability of OSiNDs‐based OSCs is attributed to the avoidance of photoinduced shunts and the photocatalytic effect, which are ineluctable shortcomings in inverted OSCs based on ZnO cathode interlayers.

Abstract

The performance and industrial viability of organic photovoltaics are strongly influenced by the functionality and stability of interface layers. Many of the interface materials most commonly used in the lab are limited in their operational stability or their materials cost and are frequently not transferred toward large‐scale production and industrial applications. In this work, an advanced aqueous‐solution‐processed cathode interface layer is demonstrated based on cost‐effective organosilica nanodots (OSiNDs) synthesized via a simple one‐step hydrothermal reaction. Compared to the interface layers optimized for inverted organic solar cells (i‐OSCs), the OSiNDs cathode interlayer shows improved charge carrier extraction and excellent operational stability for various model photoactive systems, achieving a remarkably high power conversion efficiency up to 17.15%. More importantly, the OSiNDs’ interlayer is extremely stable under thermal stress or photoillumination (UV and AM 1.5G) and undergoes no photochemical reaction with the photoactive materials used. As a result, the operational stability of inverted OSCs under continuous 1 sun illumination (AM 1.5G, 100 mW cm⁻²) is significantly improved by replacing the commonly used ZnO interlayer with OSiND‐based interfaces.