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Suns-photoluminescence approach is used to spatially resolve open-circuit voltages and pseudo-fill factors of finished and partially finished perovskite solar cells at as-prepared and degraded states. This method is used to predict the cell performance from material selection until completion early. It also allows monitoring of the uniformity and repeatability of the cell fabrication process.

Early prediction of spatially resolved performance of perovskite solar cells (PSCs) is essential for process monitoring, control and fault diagnosis, and upscaling of this emerging technology. Herein, a fast, nonde structive, contactless imaging-based approach is developed to visualize the spatial distribution of possible light current density−voltage (pseudo-J−V) curves on finished and partly finished cells. This allows for the extraction of other critical spatially resolved properties including implied open-circuit voltage and pseudo-fill factor. The technique is applied to systematically investigate various degradation behaviors on PSCs including thermal stability, light soaking, and ambient air exposure. Finally, it is used to predict pseudo-J−V curves of various perovskite films with different compositions. These results demonstrate the significant value of this fast imaging technique for the research and development of PSCs ranging from material selection, process optimization, to degradation study.

Nickel oxide serves as an inexpensive and stable charge-transporting layer for perovskite solar cells (PSCs). However, its high-temperature processing limits its applicability to low-temperature-processed devices. Herein, ligand-modified NiO nanoparticles are shown to permit low-temperature (140 °C) processing into high-quality thin films using a Tesla-valve microfluidic mixer, which are suitable for developing stable and efficient PSCs.

Nickel oxide (NiO) is used as a hole-transporting layer (HTL) in perovskite solar cells (PSCs) because of its high optical transmittance, intrinsic p-type doping, and suitable valence band energy level. However, fabricating high-quality NiO films typically requires high-temperature annealing, which limits their applicability for low-temperature, printable PSCs. Herein, the need for such postprocessing steps is circumvented by coupling 4-hydroxybenzoic acid (HBA) or trimethyloxonium tetrafluoroborate (Me₃OBF₄) ligand-modified NiO nanoparticles (NPs) with a Tesla-valve microfluidic mixer to deposit high-quality NiO films at a temperature <150 °C. The NP dispersions and the resulting thin films are thoroughly characterized using a combination of optical, structural, thermal, chemical, and electrical methods. While the optical and structural properties of the ligand-exchanged NiO NPs remain comparable with those possessing the native long-chained aliphatic ligands, the ligand-modified NiO thin films exhibit dramatic reductions in surface energy and an increase in hole mobilities. These are correlated with concomitant and significant enhancements in performance and stability factors of PSCs when the ligand-modified NiO NPs are used as HTL layers within p−i−n device architectures.

A dissymmetric backbone and selenophene substitution on the central core was employed to synthesize dissymmetric A-DA′D-A NF-SMAs. Their detailed single-crystal packing were revealed successfully. The dissymmetric A-WSSe-Cl:PM6 device presented an impressive PCE of 17.51 %, which is the highest values for selenophene-based and the dissymmetric NF-SMAs in binary PSCs.

Abstract

A dissymmetric backbone and selenophene substitution on the central core was used for the synthesis of symmetric or dissymmetric A-DA′D-A type non-fullerene small molecular acceptors (NF-SMAs) with different numbers of selenophene. From S-YSS-Cl to A-WSSe-Cl and to S-WSeSe-Cl, a gradually red-shifted absorption and a gradually larger electron mobility and crystallinity in neat thin film was observed. A-WSSe-Cl and S-WSeSe-Cl exhibit stronger and tighter intermolecular π–π stacking interactions, extra S⋅⋅⋅N non-covalent intermolecular interactions from central benzothiadiazole, better ordered 3D interpenetrating charge-transfer networks in comparison with thiophene-based S-YSS-Cl. The dissymmetric A-WSSe-Cl-based device has a PCE of 17.51 %, which is the highest value for selenophene-based NF-SMAs in binary polymer solar cells. The combination of dissymmetric core and precise replacement of selenophene on the central core is effective to improve J _sc and FF without sacrificing V _oc.

All thermally activated delayed fluorescence (TADF) single-emitting-layer white organic light-emitting diodes are developed by using a high-efficiency orange–red TADF fluorophor doped in a blue TADF fluorophor. Singlet and triplet excitons in the devices can be well shared and captured in two emitters, resulting in state-of-the-art performances with maximum external quantum efficiencies of over 30%.

Abstract

While monochrome organic light-emitting diodes (OLEDs) based on thermally activated delayed fluorescence (TADF) emitters have achieved over 30% external quantum efficiencies (EQEs), all-TADF white OLEDs (WOLEDs) are still lagging behind. Herein, a simple system based on two color-complementary TADF emitters is exploited to realize high-performance WOLEDs. By doping a high-performance orange–red TADF fluorophor (BPPZ-DPXZ) into a blue TADF host (DBFCz-Trz), energy transfer, and triplet-to-singlet conversion in the host-dopant system can be optimized to simultaneously achieve full exciton utilization and color balance. With this design, all-TADF single-emitting-layer WOLEDs with a maximum EQE up to 32.8% are demonstrated. This high efficiency surpasses EQEs of reported WOLEDs based on both TADF as well as phosphorescence. It is expected that this finding can provide new insight for designing highly efficient all-TADF WOLEDs.

A new non-fullerene acceptor named BTP1O-4Cl-C12 which contains chlorinated end groups, extended inner side chains and asymmetric alkyl and alkoxy outer side chains is reported. These modifications help BTP1O-4Cl-C12-based devices achieve high efficiency of 17.1% and show its potential application in ternary organic solar cells.

Abstract

Chemical modifications of non-fullerene acceptors (NFAs) play vital roles in the development of high efficiency organic solar cells (OSCs). In this work, on the basis of the previously reported molecule named Y6-1O, chlorination and inner side-chain engineering are adopted to endow the corresponding devices with higher open-circuit voltage (V _OC) and short-circuit current density (J _SC) as well as good morphology for high fill factor (FF). As a result, the molecule named BTP1O-4Cl-C12 can help achieve a higher power conversion efficiency (PCE) of 17.1% than that of Y6-1O (16.1%). Furthermore, the following comparisons between BTP1O-4Cl-C12 and the two symmetric acceptors named BTP2O-4Cl-C12 and BTP-4Cl-C12 demonstrate the effect of asymmetric alkoxy substitution on the outer side chains, which not only achieves a balance between V _OC and J _SC, but also help obtain appropriate morphology for efficient charge dissociation and suppressed charge recombination. Therefore, the asymmetric BTP1O-4Cl-C12 can achieve a higher PCE compared to the symmetric BTP2O-4Cl-C12 and BTP-4Cl-C12. The work not only reports an excellent NFA for high-performance OSCs, but also puts forward a series of methods for consecutive chemical modifications on Y-series acceptors, which can be further applied to boost the PCE of OSCs to a higher level.

Ethylenediamine (EDA) coating changes the p-type tin-lead perovskite to n-type, increases the built-in potential, and decreases the open-circuit voltage (V _oc) loss in perovskite solar cells. With Br inclusion into the lattice and passivation by EDA, the highest power conversion efficiency of 21.74% and Voc of 0.86 V is achieved using Cs_0.025FA_0.475MA_0.5Sn_0.5Pb_0.5I_2.975Br_0.025 perovskite film with a bandgap of 1.25 eV.

Abstract

Tin-lead perovskite solar cells (PSCs) show inferior power conversion efficiency (PCE) than their Pb counterparts mainly because of the higher open-circuit voltage (V _oc) loss. Here, it is revealed that the p-type surface of perovskite transforms to n-type, based on post-treatment by a Lewis base, ethylenediamine. This approach forms a graded band structure owing to the rise of the Fermi-energy level at the surface of the perovskite layer, and increases the built-in potential from 0.56 to 0.76 V, which increases the V _oc by more than 100 mV. It is demonstrated that EDA can lower the defect density (Sn⁴⁺ amount) by screening perovskite against oxygen, and by bonding with undercoordinated Sn on the surface. This study further explores the role of Br anion inclusion in the perovskite lattice from the viewpoint of reducing the lattice strain and Urbach energy. Finally, a high V _oc of 0.86 V is obtained, corresponding to a voltage deficit of 0.39 V, using a perovskite absorber with a bandgap of 1.25 eV and the highest PCE (21.74%) reported so far for Sn-Pb PSCs is achieved.

It is a challenge to directly grow anisotropic all-inorganic perovskite monocrystalline wires, due to the weak surface energy difference among the low index facets. A surface energy difference amplification strategy is developed to regulate the surface energy of growing nanostructures, and accordingly the anisotropic growth of CsPbBr₃ wires.

Abstract

It is a great challenge to directly grow super long all-inorganic perovskite monocrystalline wires due to the weak surface energy difference among the low index facets. Here, a one-pot solution process to grow the aspect ratio over 10⁵ of monocrystalline CsPbBr₃ perovskite wires (PWs) and yield up to 70% is reported. A chemical potential dependent surface energy difference amplification strategy is proposed to regulate the surface energy of growing and grown surfaces accordingly to the anisotropic growth of CsPbBr₃. The anisotropic growth of wires is derived from the regulation of anti-solvent diffusion kinetic and the mass transfer kinetic control of the metal halide salts. This experiment demonstrates a 50 times amplification of surface energy difference. As-produced PWs present a high photodetection responsivity up to 4923 A W⁻¹, external quantum efficiency exceeding 13 784%, and detectivity over 3.6 × 10¹³ Jones. This work not only reveals the mechanism of surface energy dominated anisotropic growth for CsPbBr₃ PWs, but also elucidates the important role of kinetics regulation during the growth process, which may open a new window for the low-dimensional crystal growth of ionic compounds.

Asymmetry and halogenation are employed to design a fused-ring non-fullerene electron acceptor, and demonstrate the synergistic effect of tuning optoelectronic properties and enhancing molecular stacking, leading to the highest device efficiency.

Abstract

Fused-ring non-fullerene electron acceptors (NFAs) boost the power conversion efficiencies (PCEs) of organic solar cells (OSCs). Asymmetric and halogenated NFAs have drawn increasing attention in recent years due to their unique optoelectronic properties. Starting from the symmetric NFA ITCC-M, this work systematically designs and synthesizes an asymmetric counterpart ITCC-M-2F, halogenated counterpart ITCC-Cl, and asymmetric and halogenated counterpart IDTT-Cl-2F. Among these NFAs, IDTT-Cl-2F shows the shallowest lowest unoccupied molecular orbital energy level, broader absorption range, and the tightest molecular packing. As a result, when blended with the donor PBDB-T-2Cl, IDTT-Cl-2F-based OSCs yield the highest PCE of 13.3% with an open-circuit voltage of 0.96 V, short-circuit current of 19.20 mA cm^–2, and fill factor of 71.1%, which is the highest PCE of OSCs employing 2-(2-chloro-6-oxo-5,6-dihydro-4H-cyclopenta[b]thiophen-4-ylidene) malononitrile (ClIC) unit terminated NFA. The results demonstrate the synergistic effect of asymmetry and halogenation toward tuning of the optoelectronic properties of NFAs for high performance OSCs.

A “two-in-one” strategy is applied to form an acceptor alloy for fine-tuning the donor/acceptor energy alignment and blend morphology. Enhanced hole transfer and suppressed charge recombination in the alloy acceptor consisting of AQx-3 and Y6 enable a power conversion efficiency of over 18%, which is the highest documented for ternary organic solar cells utilizing two nonfullerene acceptors.

Abstract

The trade-off between the open-circuit voltage (V _oc) and short-circuit current density (J _sc) has become the core of current organic photovoltaic research, and realizing the minimum energy offsets that can guarantee effective charge generation is strongly desired for high-performance systems. Herein, a high-performance ternary solar cell with a power conversion efficiency of over 18% using a large-bandgap polymer donor, PM6, and a small-bandgap alloy acceptor containing two structurally similar nonfullerene acceptors (Y6 and AQx-3) is reported. This system can take full advantage of solar irradiation and forms a favorable morphology. By varying the ratio of the two acceptors, delicate regulation of the energy levels of the alloy acceptor is achieved, thereby affecting the charge dynamics in the devices. The optimal ternary device exhibits more efficient hole transfer and exciton separation than the PM6:AQx-3-based system and reduced energy loss compared with the PM6:Y6-based system, contributing to better performance. Such a “two-in-one” alloy strategy, which synergizes two highly compatible acceptors, provides a promising path for boosting the photovoltaic performance of devices.

Incorporation of thus far unreported 1D-Tpy₂Pb₃I₆ and 2D-TpyPb₃I₆ perovskites allows to form a multidimension coupled 1D-2D-3D perovskite, which is proved to effectively release the residual strain whilst improving the carriers transport ability. Accordingly, the as-fabricated 1D-2D-3D hybrid CsPbI₂Br perovskite solar cells demonstrate high power conversion efficiency whilst extraordinary stability within 1066 h in ambient atmosphere.

Abstract

Despite the rapid development of CsPbI _x Br_{3− x} (0 ≤ x ≤ 3) inorganic perovskite solar cells, associated with their superior thermal stability, their low moisture stability limits their commercial deployment. In this study, 1D-2D-3D multidimensional coupled perovskites are prepared by means of an in situ self-integration approach. This pioneering method allows incorporating thus far unreported 1D-Tpy₂Pb₃I₆ and 2D-TpyPb₃I₆ (Tpy; terpyridine) perovskites. Heterojunction perovskites demonstrate superior stability against water in comparison with control 3D CsPbI₂Br, which is related to the hydrophobicity of low-dimension (LD) perovskites. Remarkably, the spontaneous involvement of LD perovskites can adjust/reconstruct the interfacial structure. This modification allows releasing the residual strain, establishing effective charge transfer channels that increase the carrier transport ability. Accordingly, 1D-2D-3D hybrid CsPbI₂Br perovskite solar cells demonstrate a stabilized power conversion efficiency as high as 16.1%, which represents a very significant improvement, by a factor of 43%, with respect to control 3D CsPbI₂Br perovskite solar cell. Equally importantly, the multidimensional coupled perovskite solar cells exhibit extraordinary stability, well above 1000 h in ambient atmosphere.

Three cyanoacetate-containing donor-acceptor compounds (CA, CAMA, CAFA) are designed for perovskite modifications, combining surface passivation and secondary grain growth for synergistic effects. With proper selection of cation, the optimal CAMA contributes to lower energy barriers and fewer trap states, thus accounting for CAMA-treated PSCs with higher efficiency and better stability than the reference cells.

Abstract

Interfacial engineering methods have been developed to solve defect issues of perovskite solar cells (PSCs). However, traditional surface passivation has limited effects on eliminating defect-forming residuals, while secondary grain growth (SGG) is restricted by limited choices of additives and intrinsic properties of perovskites. Here, a pincer strategy of taking advantages of surface passivation and SGG is proposed to modify both exterior and interior of CH₃NH₃PbI₃ (MAPbI₃) perovskite, by employing cyanoacetate-containing donor-acceptor compounds (CA-D-A) including 2-cyano-3-(3,4,5-trimethoxyphenyl)acrylic acid (CA), methanaminium 2-cyano-3-(3,4,5-trimethoxyphenyl)acrylate (CAMA), and aminomethaniminium (Z)-2-cyano-3-(3,4,5-trimethoxyphenyl)acrylate (CAFA). In comparison to untreated perovskite, CA-D-A treated perovskites present better crystallinity because of SGG, lower trap densities due to the synergistic effect of surface passivation and SGG, and tuned energy levels induced by CA-D-A. Accordingly, the CA-D-A treated MAPbI₃-based PSCs exhibit higher open-circuit voltage and fill factor than the control PSC without any treatment, leading to improved power conversion efficiency (PCE) and enhanced device stability, especially the CAMA treated PSCs with an average PCE promoted from 17.77 (control PSCs) to 18.71%, and importantly an excellent PCE of 19.71% through further optimization. This work provides an effective strategy for developing highly efficient and stable PSCs with the assistance of both surface passivation and SGG.

EuF _x is an excellent electron-selective material. A desired Ohmic contact can be formed between lightly doped n-type c-Si and Al by inserting 2–4 nm EuF _x films. The contact resistivity is lower than 20 mΩ cm². Combined with an ultrathin SiO₂ as a passivation layer, a champion efficiency 21.6% of n-type c-Si solar cells with full-area SiO₂/EuF _x is achieved.

Dopant-free carrier-selective contacts have attracted considerable research interests, extensively due to the avoidance of high-temperature doping and their simple, environmental-friendly fabrication processes for crystalline silicon (c-Si) solar cells. Herein, a novel dopant-free electron-selective material, europium fluoride (EuF _x ) is developed. A desired Ohmic contact can be formed between lightly doped n-type c-Si and aluminum (Al) by inserting nanoscale EuF _x films (2–4 nm) through thermal evaporation so as to avoid the high-temperature phosphorus diffusion and offer a simple, robust process. The contact resistivity is lower than 20 mΩ cm². EuF _x film can effectively select electrons and block holes at the contact interface, which is attributed to its low work function and a large valence band offset with respect to n-type c-Si. Combined with an ultrathin silicon oxide (SiO₂) as a passivation layer, a champion power conversion efficiency 21.6% of n-type c-Si solar cells with full-area SiO₂/EuF _x is achieved. An average of absolute efficiency is increased by 12% compared with the reference. The results show that EuF _x has particularly excellent electron-selective transport performance. The new possibility of using lanthanide salts as electron-selective contacts for photovoltaic (PV) devices is set up.

A novel method for subcell selective analysis of perovskite/Si tandem solar cells using a bichromatic light emitting diode (LED) light source is presented. Based on programmable LED biasing, light intensity-dependent measurements for each subcell can be conducted and subcell parameters extracted. Using a one-diode model for each subcell, their J−V characteristics can be reconstructed, providing important information about tandem operation.

In monolithic tandem solar cells, current−voltage (J−V) characteristics of subcells provide invaluable information about their quality and tandem operation. However, accessing the subcell J−Vs is challenging and requires sophisticated spectral methods. Herein, a customized, bichromatic light emitting diode setup (BCLED) for in-depth analysis of tandem solar cells, suitable for subcell operation analysis, and long-term stability testing is presented. For this, two spectrally independent LED arrays are used to selectively bias the two subcells. The power of the developed setup is demonstrated by successfully disentangling the tandem J−V curve into subcell J−V curves. The method is based on a one-diode model for each subcell and is validated by electrical simulations. Afterward, it is used on a fabricated 27.6% efficient perovskite/silicon tandem device, resulting in great agreement with the measured J−V curve. Therefore, the BCLED setup is a versatile tool, suitable for subcell characteristics and long-term stability analysis of tandem solar cells.

Hydrophobic organic ammonium halides (Cl, Br, and I) are used for the modification of inorganic CsPb(I_0.75Br_0.25)₃ perovskite solar cells. Benefiting from their passivation effects and hydrophobic long alkyl chain, the modified devices exhibit enhanced efficiency and stability. Among them, the hexadecyltrimethylammonium chloride (CTAC)-modified device shows the best performance with a power conversion efficiency (PCE) of 18.05%.

Inorganic cesium lead halide perovskite solar cells are promising candidates for next-generation photovoltaic applications. However, their phase instability and relatively low efficiency hinder their commercialization. Herein, hydrophobic organic ammonium halides (Cl, Br, and I) are rationally used for the modification of inorganic CsPb(I_0.75Br_0.25)₃ perovskite solar cells. Benefiting from their passivation effects and hydrophobic long alkyl chain, the modified devices exhibit enhanced efficiency and stability. Among them, the hexadecyltrimethylammonium chloride (CTAC)-modified device shows the best performance with a power conversion efficiency (PCE) of 18.05%. Furthermore, a gradient triple anion inorganic perovskite CsPb(I_0.75Br_0.25)_3−x Cl _x layer is formed in situ during the CTAC modification, which demonstrates better phase stability than CsPb(I_0.75Br_0.25)₃. As a result, the modified device also shows excellent stability, maintaining 94% of the initial efficiency after 35 days in N₂ atmosphere.

The in situ optical spectra reveal a significantly prolonged crystallization window during the perovskite deposition via additive strategy. Finer thickness gradient by n values in the direction orthogonal to the substrate leads to more efficient charge transport between quantum wells and suppressed charge recombination in the additive-treated film. Finally, the power conversion efficiency of 14.4% is obtained.

Abstract

New structural type of 2D AA′ _{n −1}M _n X_{3 n +1} type halide perovskites stabilized by symmetric diammonium cations has attracted research attention recently due to the short interlayer distance and better charge-transport for high-performance solar cells (PSCs). However, the distribution control of quantum wells (QWs) and its influence on optoelectronic properties are largely underexplored. Here effective phase-alignment is reported through dynamical control of film formation to improve charge transfer between quantum wells (QWs) for 2D perovskite (BDA)(MA) _{n -1}Pb _n I_{3 n +1} (BDA = 1,4-butanediamine, 〈n〉 = 4) film. The in situ optical spectra reveal a significantly prolonged crystallization window during the perovskite deposition via additive strategy. It is found that finer thickness gradient by n values in the direction orthogonal to the substrate leads to more efficient charge transport between QWs and suppressed charge recombination in the additive-treated film. As a result, a power conversion efficiency of 14.4% is achieved, which is not only 21% higher than the control one without additive treatment, but also one of the high efficiencies of the low-n (n ≤ 4) AA′ _{n −1}M _n X_{3 n +1} PSCs. Furthermore, the bare device retains 92% of its initial PCE without any encapsulation after ambient exposure for 1200 h.

The quadrupole moment of non-fullerene acceptors (NFAs) is an important parameter, which controls exciton quenching, charge generation, and recombination in NFA-based blends. Using two structurally similar NFAs, namely, O-IDTBR and O-IDTBCN, with very different quadrupole moments (Q₂₀), the precise impact on efficiency-limiting processes is revealed by a combination of computational and transient optical and electro-optical spectroscopy studies.

Abstract

Advancing non-fullerene acceptor (NFA) organic photovoltaics requires the mitigation of the efficiency-limiting processes. Acceptor end-group and side-chain engineering are two handles to tune properties, and a better understanding of their specific impact on the photophysics could facilitate a more guided acceptor design. Here, the device performance, energetic landscape, and photophysics of rhodanine and dicyanovinyl end-capped IDT-based NFAs, namely, O-IDTBR and O-IDTBCN, in PCE10-based solar cells are compared by transient optical and electro-optical spectroscopy techniques and density functional theory calculations. It is revealed how the acceptors’ quadrupole moments affect the interfacial energetic landscape, in turn causing differences in exciton quenching, charge dissociation efficiencies, and geminate versus non-geminate recombination losses. More precisely, it is found that the open circuit voltage (V _OC) is controlled by the acceptors’ electron affinity (EA), while geminate and non-geminate recombination, and the field dependence of charge generation, rely on the acceptors’ quadrupole moments. The kinetic parameters and yields of all processes are determined, and it is demonstrated that they can reproduce the performance differences of the devices’ current–voltage characteristics in carrier drift-diffusion simulations. The results provide insight into the impact of the energetic landscape, specifically the role of the quadrupole moment of the acceptor, beyond trivial considerations of the donor–acceptor energy offsets.

Ultrathin and ultra-lightweight organic solar cells (total thickness of less than 3 μm) with a stabilized power conversion efficiency of 15.5% and unprecedented power-per-weight of 32.07 W g⁻¹ at a weight of 4.83 g m⁻² are realized, which could be applied to almost any surface of wearable electronic devices, and can withstand the associated mechanical deformation.

Abstract

Ultraflexible and ultra-lightweight organic solar cells (OSCs) have attracted great attention in terms of power supply in wearable electronic systems. Here, ultrathin and ultra-lightweight OSCs, with a total thickness of less than 3 µm, with excellent mechanical properties in terms of their flexibility and ability to be stretched are demonstrated. A stabilized power conversion efficiency (PCE) of 15.5% and unprecedented power-per-weight of 32.07 W g⁻¹ at a weight of 4.83 g m⁻² is achieved, which represents one of the best-performing OSCs based on ultrathin foils substrate reported to date. The ternary strategy introduces the third component of amorphous conformation of the PC₇₁BM molecule, which can slightly reduce crystallization and aggregates without decreasing the electron mobility, thereby reducing rigidity and brittleness of the active layer. The increase in the ductility of the active layer significantly improves the mechanical flexibility of the device, resulting in over 90% retention in the PCE after 200 stretching–compression cycles. In addition, the ternary device exhibits excellent stability when stored in a N₂-filled glove box, resulting in the PCE retaining over 95% of its initial efficiency even after 1000 h. This ultraflexible and ultra-lightweight photovoltaic foils constitute a major step toward the integration of power supply into malleable electronic textiles.

The design principle for lead-free perovskites and the progress of typical lead-free perovskite photodetectors are reviewed and discussed. The outlook for future research and applications is then explored.

Abstract

State-of-the-art photodetectors which apply hybrid perovskite materials have emerged as powerful candidates for next-generation light sensing. Among them, lead-based ones are the most popular beyond doubt on account of their unique and superior optoelectronic properties. Nevertheless, trade-off toward commercialization exists between nontoxicity and high performance, with the poor stability of lead-based perovskites, indicating that it is indispensable to substitute lead with nontoxic element meanwhile bringing about a comparable figure of merit of photodetectors and relatively long-term stability. Herein, recent advances in lead-free perovskite photodetectors are reviewed, analyzing the principle while designing new materials and highlighting some remarkable progress, which are comparable, even superior, to lead-based photodetectors. Furthermore, their potential strategy in optical communication, image sensing, narrowband photodetection, etc., is examined and a perspective on developing new materials and photodetectors with superior properties for more practical applications is provided.

Chiral perovskites are considered to be a promising class of materials for next-generation optoelectronic and spintronic devices, owing to their superiority in combining chirality and high dielectric constants, high optical-absorption coefficients, and strong spin–orbit coupling. The synthesis strategies, chirality generation mechanisms, physical properties, and applications of chiral perovskites are reviewed.

Abstract

Chiral materials with intrinsic inversion-symmetric structures possess many unique physicochemical features, including circular dichroism, circularly polarized photoluminescence, nonlinear optics, ferroelectricity, and spintronics. Halide perovskites have attracted considerable attention owing to their excellent optical and electrical properties, which are particularly suitable for realizing high power-conversion efficiency in solar cells. Recent studies have shown that chirality can be transferred from chiral organic ligands into halide perovskites and the resultant chiral perovskites combine the advantages of both chiral materials and halide perovskites; this provides an ideal platform to design next-generation optoelectronic and spintronic devices. In this progress report, the most recent advances are summarized in various chemical structures of chiral perovskites, their synthesis strategies, chirality generation mechanisms, and physical properties. Furthermore, the potential chiral-halide-perovskite-based applications are presented and the challenges and prospects of chiral perovskites are discussed. This report outlines the diverse construction strategies of and proposes research directions for chiral halide perovskites; thus, it provides insights into the design of novel chiral perovskites and facilitates investigation of the optoelectronic applications that employ chirality.

Metallic lithium is applied to n-type crystalline silicon wafers and proven to be an excellent electron-selective, hole-blocking transport layer, yielding a low contact resistivity. By implementing a full-area electron-selective lithium contact, n-type c-Si solar cells with a fill factor of 81%, and efficiency of 19% are achieved.

Abstract

Separating photogenerated charge carriers by carrier-selective heterostructure contacts rather than by doped homojunctions is a promising pathway to approach the theoretical power conversion efficiency (PCE) limit of crystalline silicon (c-Si) solar cells. An electron-selective, hole-blocking lithium contact for c-Si solar cells is presented by simple thermal evaporation of air-stable Li₃N powder. It is found that this lithium contact introduces only a minimal Schottky-barrier height for electron transport at its interface with lightly doped n-type c-Si surfaces, resulting in a low contact resistivity of 12.8 mΩ cm². By implementing a full-area electron-selective lithium contact, an n-type c-Si solar cell with a PCE of 19% is achieved, representing a 4% absolute PCE improvement over reference devices with an aluminum contact. The choices of electron-selective contact materials for photovoltaic devices, using simple, scalable fabrication methods are extended.

This study reveals that Cu may act as a suitable electrode material for perovskite solar cells judging from both the in situ photoemission spectroscopy results and prototype device tests. The detailed insight obtained from the fundamental understanding can provide essential guidelines to advance the development of superior perovskite solar cells.

Abstract

In this study, the electronic properties and chemical stability of the Cu/CH₃NH₃PbI₃ interface are investigated in situ by a combination of X-ray photoelectron spectroscopy and synchrotron radiation photoemission spectroscopy (SRPES). The morphology of Cu deposited perovskite surface is monitored by scanning electron microscopy. The results show that the Cu/CH₃NH₃PbI₃ interface is very stable and no chemical reaction between Cu and the perovskite takes place. Moreover, a 0.45 eV interface dipole and a 0.15 eV upward band bending are obtained at the Cu/CH₃NH₃PbI₃ interface. Based on these fundamental findings, a prototype of Cu/CH₃NH₃PbI₃/NiO _x /indium tin oxide solar cell device is constructed to check the power conversion efficiency (PCE) and device stability. Although no electron transport material is used in this device, it still exhibits decent performance. The PCE of the device reaches up to 9.99% and remains almost unchanged over a long-time (49 d) storage in a N₂-filled glovebox. Through this study it is demonstrated that fundamental understanding of the interfacial structure of a perovskite solar cell is essential in pursuit of rational design of superior perovskite solar cells, and moreover, Cu is a promising electrode candidate for perovskite solar cells.