吴晓晓

Two regular terpolymers are used as the effective dopant-free hole transport materials for inverted perovskite solar cells. The power conversion efficiency of solar cells can reach up to 18.17%, with negligible hysteresis and good ambient stability, which is mainly due to the well-matched energy level, improved film morphology, low carrier recombination, and higher hole extraction efficiency of the perovskite layer.

In inverted perovskite solar cells (PSCs), hole transport materials (HTMs) can efficiently improve hole extraction and transfer as well as the crystallization of perovskite films and thus enhance the photovoltaic performance. Herein, two dopant-free, regular A₁–D–A₂–D-type (D: electron donor; A: electron acceptor) polymeric HTMs, PTPDTBT and PDPPTBT, are developed by integrating the benzothiadiazole unit (A₁) with the electron-accepting species of either a thieno[3,4-c]pyrrole-4,6-dione or a pyrrolo[3,4-c]pyrrole-1,4-dione segment (A₂), respectively, where the thiophene unit (D) results in a kinked molecular geometry. These A₁–D–A₂–D-type terpolymers exhibit comparable nonpolar properties but distinct film-quality morphology and charge transport characteristics. PDPPTBT with the more insulating side-chain groups is found to improve the quality of perovskite films cast on top with larger grain sizes and more homogeneous crystallization. As a consequence, the PDPPTBT-based PSCs without any dopants and additional interlayers display a champion power conversion efficiency of 18.17%, one of the highest values of MAPbI₃-based inverted PSCs using dopant-free D-A-type polymeric HTMs. Furthermore, the PDPPTBT-based device exhibits negligible hysteresis and high long-term stability. This work provides a potential strategy to design dopant-free A₁–D–A₂–D-type polymeric HTMs for efficient and stable PSCs.

Perovskite solar cells are poised to take the next step into commercialization. Hole-transporting materials are central components of these devices, which determine the actual efficiency and durability by controlling interfacial charge extraction/transport processes and exchanges with the external environment. Herein, the evolution in the engineering of these layers is analyzed, revealing their “non-innocent role” in driving device performance.

The race to the future generation of low-cost photovoltaic devices continuously takes on added momentum with the appearance of novel practical solutions for the fabrication of perovskite solar cells (PSCs), a paradigm technology for ultracheap light-to-electricity conversion. Much has been done in the past few years toward defining standard protocols for the assessment of their efficiency and stability, aiming at achieving a worldwide consensus on the issue, that will allow reliable reporting of new data. While this is undoubtedly a step ahead toward commercialization of these devices, it also often triggers researchers to test record architectures using benchmark configurations, mainly for what regards the ancillary layers that extract electrical charges from the photoexcited perovskite. In particular, the mostly used hole-transporting material (HTM) is the small-molecule spiro-OMeTAD, which is also well known to be the origin of PSC degradation after prolonged operation. Herein, it is aimed to remark the huge impact of the HTM on PSC performance, recalling major issues associated with the conventional spiro-based one and providing an overview of state-of-the-art alternatives. Finally, possible scenarios for the future development of smart HTMs are also envisioned, as charge-extracting layers, with a real active role in ensuring PSC operational stability.

The efficiency potential of various solar cells is analyzed to develop high-efficiency solar cell modules for photovoltaic (PV)-powered vehicles. Analytical and practical data show that the III−V and Si 3-junction tandem solar cell modules with an efficiency of more than 30% have a potential driving range of 30 km day⁻¹ on average and more than 50 km day⁻¹ on a clear day.

Photovoltaic (PV)-powered vehicles are expected to play a critical role in a future carbon neutral society because it has been reported that the onboard PVs have great ability to reduce CO₂ emission from the transport sector. Although the demonstration car with a III−V-based solar cell module has shown the PV-powered driving range of 36.6 km day⁻¹ at solar irradiance of 6.2 kWh m⁻² day⁻¹, practical driving ranges of PV-powered vehicles are shown to be lower than estimated values due to some losses such as nonradiative recombination and resistance losses of solar cell modules under sunshine condition. This article presents analytical results for the effects of illumination intensity properties of various solar cell modules on the PV-powered driving range to develop highly efficient solar cell modules for vehicle-integrated applications. The analysis shows that improvements in shunt resistance and saturation current density of solar cell modules are necessary to improve illumination intensity properties of solar cell modules under low intensity sunshine condition. The calculations show that the III−V-based 3-junction solar cell modules with an efficiency of more than 30% have a potential PV-powered driving range of 30 km/day average and more than 50 km day⁻¹ on a clear day.

The control of molecular packing through hydrogen-bond-directed self-assembly bestows robustness to the structure of hole transporting layers (HTL). A comparative study between two analogous pyrene-based small molecules proves that self-assembled HTLs benefit the solution processing of Pb–Sn perovskite solar cells and improve their efficiency and stability, outperforming poly(3,4-ethylenedioxythiophene):polystyrene sulfonate (PEDOT:PSS).

Lead–tin (Pb–Sn) hybrid perovskite materials possess ideal narrow bandgaps (1.2–1.4 eV) for efficient single-junction and tandem solar cells. Poly(3,4-ethylenedioxythiophene):polystyrene sulfonate (PEDOT:PSS) is commonly used as hole transport layer (HTL) for Pb–Sn perovskite solar cells (PSCs), despite its poor stability with these perovskites. Here, two new octacyclic heteroaromatic molecules, pyrenodiindole (PDI) and pyrenodi-(7-azaindole) (PDAI), are presented as the HTL for narrow-bandgap (1.23 eV) p–i–n Pb-Sn PSCs. The self-assembled reciprocal hydrogen-bonded solid-state structure of PDAI bestows robustness compared to PDI, making it less vulnerable in processing the perovskite film on top, and improves the reproducibility of device fabrication. Transient photocurrent measurements and light-intensity-dependent device characteristics indicate that PDI and PDAI possess similar hole extraction properties to PEDOT:PSS. As a result, similar open-circuit voltages and fill factors are obtained in the PSCs. Interestingly, the use of thin PDI and PDAI as HTL in PSCs changes the optical interference and reduces parasitic absorption in the near-infrared region, resulting in an improved short-circuit current density. Consequently, a higher power conversion efficiency of 16.1% is obtained for PDI and PDAI, compared to 15.1% for PEDOT:PSS. In addition, the self-assembled structure of PDAI led to a notable enhancement of device stability.

An environmentally benign material, histamine (HA), is used to intentionally passivate the V_I in the CsPbI_3−x Br _x perovskite thin films. The synergistic effect of Lewis base–acid interaction and H-bond strengthens the adsorption of HA molecules on the surface of perovskite. The fabricated PSCs with HA passivation significantly reduced the number of uncoordinated Pb²⁺ and achieved a record 20.8 % efficiency.

Abstract

Iodine vacancies (V_I) and undercoordinated Pb²⁺ on the surface of all-inorganic perovskite films are mainly responsible for nonradiative charge recombination. An environmentally benign material, histamine (HA), is used to passivate the V_I in perovskite films. A theoretical study shows that HA bonds to the V_I on the surface of the perovskite film via a Lewis base–acid interaction; an additional hydrogen bond (H-bond) strengthens such interaction owing to the favorable molecular configuration of HA. Undercoordinated Pb²⁺ and Pb clusters are passivated, leading to significantly reduced surface trap density and prolonged charge lifetime within the perovskite films. HA passivation also induces an upward shift of the energy band edge of the perovskite layer, facilitating interfacial hole transfer. The combination of the above raises the solar cell efficiency from 19.5 to 20.8 % under 100 mW cm⁻² illumination, the highest efficiency so far for inorganic metal halide perovskite solar cells (PSCs).

An ultralow surface temperature on perovskite films is constructed, then surface perovskite lattice is etched by the condensed moisture. Therefore, PbI₂ is produced and type-I band alignment at the upper surface grain boundaries is formed, which significantly reduces the interface loss of carriers and improves the efficiency of perovskite solar cells to 23.2%.

Abstract

The open-circuit voltage (V _OC) of perovskite solar cells (PSCs) is reported to be significantly weakened by carrier loss at the film surface. Here, the moisture condensation at only the upper surface of perovskite films is controlled by constructing an ultralow surface temperature. Then, type-I band alignment can be formed at the surface grain boundaries due to the etching effect of trace amounts of condensed moisture. The beneficially constructed surface type-I band alignment can effectively repel carriers and return them to the inside of the grain, significantly avoiding the carrier loss at films surface. As a result, a superior carrier lifetime exceeding 2.5 µs is obtained and the V _OC of PSC is remarkably boosted from 1.07 to 1.17 V. The minimum V _OC deficit of only 0.39 V enables a substantial gain in power conversion efficiency (PCE) from 20.2% to 22.4% in one-step spin-coating methods. Moreover, this innovation is versatile and a champion PCE of 23.2% is also achieved in two-step spin-coating methods.

A new polymer, PDTDT, is developed as hole-transporting material for CsPbI₂Br solar cells. Using PDTDT, an ultra-high efficiency of 17.36% with V _OC of 1.42 V under one sun and 34.20% with V _OC of 1.14 V under 200 lux indoor light are achieved. The PDTDT-based cells also show superior/comparable stability to dopant-free P3HT reference.

Abstract

To abate the issue of moisture-assisted phase transition of CsPbI₂Br, caused by hygroscopic dopants used in the hole-transporting material (HTM), developing dopant-free HTMs is necessary. In this work, a new polymer, PDTDT, is developed as a dopant-free HTM for CsPbI₂Br solar cells, and the device performance and stability are systematically compared with cells employing dopant-free P3HT. CsPbI₂Br solar cells using PDTDT show an efficiency of 17.36% with V _OC of 1.42 V and FF of 81.29%, which is one of the highest values for CsPbI₂Br cells. Moreover, a record-high efficiency of 34.20% with V _OC of 1.14 V under 200 lux indoor light illumination and efficiency of 14.54% (certified efficiency of 13.86%) for a 1 cm² device under one sun are accomplished. Importantly, PDTDT shows superior/comparable device stability to P3HT, promising its potential to be an alternative to popular doped Spiro-OMeTAD and P3HT HTM.

A thiadiazole-based polymer donor (PB2F) with an ultradeep highest occupied molecular orbital level and high electroluminescence is reported. In organic solar cell (OSC) devices, PB2F exhibits a power conversion efficiency (PCE) of 14.5% after blending with IT-4F, one of highest values among the IT-4F-based OSCs, and an outstanding PCE of 18.6% in the context of ternary OSC.

Abstract

Under the premise of ensuring favorable bulk heterojunction morphology in organic solar cells (OSCs), conjugated polymer donors with deep-lying highest occupied molecular orbital (HOMO) levels are highly important to improve power conversion efficiencies (PCEs) by reducing photovoltage loss. However, the development of such materials has lagged. Herein, a thiadiazole-based conjugated polymer, PB2F is reported, which has a very deep HOMO level of −5.64 eV, and high electroluminescence quantum efficiency of 3.9 × 10⁻³. In OSCs, the PB2F-based OSC gives an excellent PCE of 14.5% with an ultrahigh open-circuit voltage (V _OC) of 0.957 V by blending with an electron acceptor of IT-4F. More importantly, the PB2F as a third component is added into the PBDB-TF:BTP-eC9 blend to achieve an outstanding PCE of 18.6% (certified PCE 18.2%), which is one of the highest PCEs in OSCs.

Although organic photovoltaics have been established to be a promising candidate for indoor light recycling, standardized testing conditions to quantify their performance are still lacking. Therefore, a method to calculate the efficiency of solar cells on the basis of relative emission spectra, quantum efficiency and current-density-voltage measurements, which enables a fair ranking of champion solar cells, is proposed.

Abstract

With increasing efficiencies of non-fullerene acceptor-based organic solar cells, thin-film technology is becoming a promising candidate for indoor light harvesting applications. However, the lack of standardized comparison methods makes it difficult to quantify progress and to compare indoor performance. Herein, a simple method to calculate the efficiency of solar cells under any possible light source and illuminance with only using simple standard measurements (current–voltage curves and quantum efficiency) is presented. Thereby, equal evaluation conditions are ensured, so that indoor solar cells can be ranked and compared according to their efficiency. Efficiencies are shown to typically vary by ±20% when using different different light emitting diode spectra with color temperatures ranging from 2700 to 6500 K. Calculations based on a detailed balance model indicate that the optimal bandgap of the absorber material depends on the used light source and ranges between 1.75 and 2 eV. The approach is validated by comparison with literature data and many calculated efficiencies match well with experimental data obtained with a specific light source. However, some reported efficiencies cannot be reproduced with the model, which highlights the need to reassess low light measuring techniques. Furthermore, a script is provided for use by the community.

Co-evaporation methylammonium formamidinium lead iodide perovskites are investigated and different aspects of stability are addressed. The influence of the perovskite composition on the performance and the long-term stability of the resulting solar cells is studied. Monolithic fully textured perovskite/silicon tandem solar cells with co-evaporated perovskite absorber are realized. These tandem cells reach an efficiency of 24.6% and exhibit minimal reflection losses.

Abstract

Formamidinium iodide (FAI) based perovskite absorbers have been shown to be ideal candidates for highly efficient and operationally stable perovskite solar cells (PSC). A major challenge for formamidinium lead iodide (FAPbI₃) is to suppress the phase transition from the photoactive black phase into yellow nonperovskite δ-phase. Several approaches to stabilize the black phase have been developed for solution-based perovskites, whereas so far, vacuum-deposited FAPbI₃ has rarely been reported. This study demonstrates the preparation of FAPbI₃ by co-evaporation and discusses the influence of the subjacent hole transporting layer (HTL) on its phase stability. By using FAI excess in the evaporation process in combination with phosphonic acids groups from the HTL, the black perovskite phase is stabilized at room temperature. Further addition of 32–59% methylammonium iodide (MAI) during the co-evaporation process leads to good absorption properties and high PSC efficiencies of 20.4%. In addition, excellent stability is achieved for optimized MAI to FAI ratios, maintaining 100% of the initial PSC performance after 1000 h under constant operation. This highly stable perovskite composition enables the first monolithic fully textured perovskite/silicon tandem solar cells with co-evaporated perovskite absorbers. Due to the conformally covered pyramid texture, these tandem cells show minimal reflection losses and reach an efficiency of 24.6%.

Solid additives are demonstrated to enhance the initial device efficiency as well as the operational lifetime of nonfullerene organic solar cells, via solid-additive-mediated aggregation control.

Abstract

The additive strategy is widely used in optimizing the morphology of organic solar cells (OSCs). The majority of additives are liquid with high boiling points, which will be trapped within device and consequently deteriorate performance during operation. In this work, solid but volatile additives 2-(4-fluorobenzylidene)-1H-indene-1,3(2H)-dione (INB-F) and 2-(4-chlorobenzylidene)-1H-indene-1,3(2H)-dione (INB-Cl) are designed to replace the common 1,8-diiodooctane (DIO) in nonfullerene OSCs. These additives present during solution casting but evaporate after moderate heating. Molecular dynamics simulations show that they can reduce the adsorption energy to improve π-π stacking among nonfullerene acceptor (NFA) molecules, an effect that enhances light absorption and electron mobility. Both INB-F and INB-Cl enhance efficiency, with INB-F achieving a maximum efficiency of 16.7% from 15.1% of the reference PBDB-T-2F (PM6):BTP-BO-4F (Y6-BO) cell, and outperforming DIO. Remarkably, they can simultaneously enhance the operational stability, with the INB-F-treated OSC maintaining over 60% of the initial efficiency after 1000 h operation, demonstrating a T ₈₀ lifetime of 523 h, which is a significant improvement over T ₈₀ values of 66.2 h for the reference and 6.6 h for DIO-treated OSC. The simultaneously enhanced efficiency and operational lifetime are also effective in PM6:BTP-BO-4Cl (Y7-BO) OSCs, demonstrating a universal strategy to improve the performance of OSCs.

A versatile co-evaporation approach to create perovskites layers with graded energy levels favorable for different device architectures is demonstrated. The p-i-n perovskite solar cells, incorporating co-evaporated MAPbI₃ with customized graded Fermi levels, achieve power conversion efficiency over 20% with different hole transporting layers and champion values of 20.6%, 19.1%, and 17.2% for 0.086, 1, and 1.96 cm² active areas, respectively.

Abstract

Recent progress of vapor-deposited perovskite solar cells (PSCs) has proved the feasibility of this deposition method in achieving promising photovoltaic devices. For the first time, it is probed the versatility of the co-evaporation process in creating perovskite layers customizable for different device architectures. A gradient of composition is created within the perovskite films by tuning the background chamber pressure during the growth process. This method leads to co-evaporated MAPbI₃ film with graded Fermi levels across the thickness. Here it is proved that this growth process is beneficial for p-i-n PSCs as it can guarantee a favorable energy alignment at the charge selective interfaces. Co-evaporated p-i-n PSCs, with different hole transporting layers, consistently achieve power conversion efficiency (PCE) over 20% with a champion value of 20.6%, one of the highest reported to date. The scaled-up p-i-n PSCs, with active areas of 1 and 1.96 cm², achieved the record PCEs of 19.1% and 17.2%, respectively, while the flexible PSCs reached a PCE of 19.3%. Unencapsulated PSCs demonstrate remarkable long-term stability, retaining ≈90% of their initial PCE when stored in ambient for 1000 h. These PSCs also preserve over 80% of their initial PCE after 500 h of thermal aging at 85 °C.

Electronic skin is a type of soft electric device that possesses various sensing capabilities like the human skin. In this review, the strategies to realize the versatile functionalities of e-skin, including strain-, pressure-, shear force-, temperature- and humility-sensing abilities, as well as self-healing ability and other functions are summarized.

Abstract

Inspired by the human skin, electronic skins (e-skins) composed of various flexible sensors, such as strain sensor, pressure sensor, shear force sensor, temperature sensor, and humility sensor, and delicate circuits, are emerged to mimic the sensing functions of human skins. In this review, the strategies to realize the versatile functionalities of natural skin-like e-skins, including strain-, pressure-, shear force-, temperature- and humility-sensing abilities, as well as self-healing ability and other functions are summarized. Some representative examples of high-performance e-skins and their applications are outlined and discussed. Finally, the outlook of the future of e-skins is presented.

A high-performance photodetector based on an all-inorganic CsPbBr₃ perovskite nanocrystals/2D non-layered cadmium sulfide selenide heterostructure is demonstrated through energy band engineering with designed typed-II heterostructure. Compared with pure CsPbBr₃ NCs and 2D-non-layered cadmium sulfide selenide devices, the responsivity of the heterostructure photodetector is enhanced by 406 times and 59 times, and the detectivity is improved over 700% and 1100%, respectively.

Abstract

Perovskites have attracted intensive attention as promising materials for the application in various optoelectronic devices due to their large light absorption coefficient, high carrier mobility, and long charge carrier diffusion length. However, the performance of the pure perovskite nanocrystals-based device is extremely restricted by the limited charge transport capability due to the existence of a large number of the grain boundary between perovskite nanocrystals. To address these issues, a high-performance photodetector based on all-inorganic CsPbBr₃ perovskite nanocrystals/2D non-layered cadmium sulfide selenide heterostructure has been demonstrated through energy band engineering with designed typed-II heterostructure. The photodetector exhibits an ultra-high light-to-dark current ratio of 1.36 × 10⁵, a high responsivity of 2.89 × 10² A W⁻¹, a large detectivity of 1.28 × 10¹⁴ Jones, and the response/recovery time of 0.53s/0.62 s. The enhancement of the optoelectronic performance of the heterostructure photodetector is mainly attributed to the efficient charge carrier transfer ability between the all-inorganic CsPbBr₃ perovskites and 2D cadmium sulfide selenide resulting from energy band alignment engineering. The charge carriers’ transfer dynamics and the mechanism of the CsPbBr₃ perovskites/2D non-layered nanosheets interfaces have also been studied by state-state PL spectra, fluorescence lifetime imaging microscopy, time-resolved photoluminescence spectroscopy, and Kelvin probe force microscopy measurements.

Advanced Functional Materials, Volume 31, Issue 30, July 23, 2021.

The suitability of substrate materials for co-evaporated perovskite solar cells is commonly assessed via heuristic approaches. Here, a universal guideline for the choice of substrate material is developed by investigating the thin-film formation of co-evaporated perovskite absorbers on various substrate materials. The guideline enables a targeted screening of substrate materials based on their surface characteristics enabling efficient all-evaporated perovskite solar cells.

Abstract

Vacuum-based deposition of optoelectronic thin films has a long-standing history. However, in the field of perovskite-based photovoltaics, these techniques are still not as advanced as their solution-based counterparts. Although high-efficiency vacuum-based perovskite solar cells reaching power conversion efficiencies (PCEs) above 20% are reported, the number of studies on the underlying physical and chemical mechanism of the co-evaporation of lead iodide and methylammonium iodide is low. In this study, the impact of one of the most crucial process parameters in vacuum processes—the substrate material—is studied. It is shown that not only the morphology of the co-evaporated perovskite thin films is significantly influenced by the surface polarity of the substrate material, but also the incorporation of the organic compound into the perovskite framework. Based on these studies, a selection guide for suitable substrate materials for efficient co-evaporated perovskite thin films is derived. This selection guide points out that the organic vacuum-processable hole transport material 2,2″,7,7″-tetra(N,N-di-p-tolyl)amino-9,9-spirobifluorene is an ideal candidate for the fabrication of efficient all-evaporated perovskite solar cells, demonstrating PCEs above 19%. Furthermore, building on the insights into the formation of the perovskite thin films on different substrate materials, a basic crystallization model for co-evaporated perovskite thin films is suggested.

Integrating a thin bulk-heterojunction layer composed of the typical poly (3-hexylthiophene-2,5-diyl) and [6,6]-phenyl methyl C61 butyric acid methyl ester (P3HT:PCBM) in a carbon-based all inorganic CsPbIBr₂ perovskite solar cell can effectively suppress interfacial energy loss and greatly improve the power conversion efficiency from 8,87% to 11.54%, which is also at the highest efficiency level of the reported counterparts.

The CsPbIBr₂ perovskite has obvious advantages in balancing the stability and efficiency in inorganic perovskite solar cells (PSCs). Its large bandgap of 2.08 eV, which leads to a narrow spectral absorption (<600 nm), is the key limit to yielding a high power conversion efficiency (PCE). Herein, it is demonstrated that by integrating a thin bulk-heterojunction (BHJ) layer (19 nm) composed of the typical poly (3-hexylthiophene-2,5-diyl) and [6,6]-phenyl methyl C61 butyric acid methyl ester (P3HT:PCBM) with CsPbIBr₂ perovskite, a carbon-based all-inorganic PSC achieves a much higher champion PCE (11.54%) than the original CsPbIBr₂ device (8.87%), and the value is also at the highest PCE level of all-inorganic CsPbIBr₂ PSCs. The integration of a thin BHJ layer brings an expanded light absorption range, better charge transfer dynamics, suppressed interfacial energy loss, and improved long-term stability. The unencapsulated CsPbIBr₂ PSC with an integrated BHJ layer shows excellent long-term stability in an ambient atmosphere with high relative humidity (RH ≈ 45%, T ≈ 25 °C). Therefore, the BHJ integration is an effective strategy on the road to industrialization of carbon-based all-inorganic PSCs with low cost, high efficiency, and excellent long-term stability.

The effect of absorber stoichiometry in wide-gap ACIGS solar cells is revised. A strong and opposing effect on J _SC and V _OC is found. With increasing [I]/[III] values > 0.9, V _OC continuously decreases, while charge carrier collection increases. Observations can be explained by decreasing absorber doping toward stoichiometric composition. The results indicate a very low diffusion length in wide-gap ACIGS films.

The effect of absorber stoichiometry in (Ag,Cu)(In,Ga)Se₂ (ACIGS) solar cells with bandgaps (E _g) > 1.40 eV is studied on a large sample set. It is confirmed that moving away in composition from ternary AgGaSe₂ by simultaneous reduction in Ga and Ag content widens the chalcopyrite single-phase region and thereby reduces the amount of ordered vacancy compounds (OVCs). As a consequence, a distortion in current−voltage characteristics, ascribed to OVCs at the back contact, can be successfully avoided. A clear anticorrelation between open-circuit voltage (V _OC) and short-circuit current density (J _SC) is detected with varying absorber stoichiometry, showing decreasing V _OC and increasing J _SC values for [I]/[III] > 0.9. Capacitance profiling reveals that the absorber doping gradually decreases toward stoichiometric composition, eventually leading to complete depletion. It is observed that only such fully depleted samples exhibit perfect carrier collection, evidencing a very low diffusion length in wide-gap ACIGS films. The results indicate that OVCs at the surface play a minor or passive role for device performance. Finally, a solar cell with V _OC = 0.916 V at E _g = 1.46 eV is measured, which is, to the best of our knowledge, the highest value reported for this bandgap to date.

Further large-scale photovoltaic deployment mandates the reduction of scarce Ag, typically comprising the metallic contact of solar cells. Electrodeposited Cu contacts are demonstrated for the first time on single-junction FA_0.75Cs_0.25Pb(I_0.8Br_0.2)₃ perovskite solar cells (PSCs) using an atomic layer deposition (ALD) Al₂O₃ masking layer on ITO. The stable photoconversion efficiency after Cu²⁺ reduction confirms that PSCs can survive wet-chemical plating process.

Electroplated copper contacts on small-area single-junction perovskite solar cells (PSCs) using an atomic layer deposited (ALD) Al₂O₃ masking layer on ITO are demonstrated for the first time. The photoconversion efficiency of ≈11% after manufacturing the Cu contacts confirms that PSCs can survive the wet-chemical plating process. From the successful realization of plated contact fingers, the creation of an electrical contact between the Cu electrode and the ITO on the FA_0.75Cs_0.25Pb(I_0.8Br_0.2)₃ perovskite absorber is inferred. Furthermore, scanning electron microscopy (SEM) with energy-dispersive X-ray (EDX) analysis shows the formation of a compact interface between ITO and plated Cu. An additional plating approach, using self-passivated aluminum as mask, allows to produce well-defined 30 μm wide Cu contacts on the PSC. Such a plating process allows for plating a low-resistive Cu grid simultaneously on both sides of a perovskite silicon heterojunction tandem solar cell with TCO, independent of substrate size.

A general and effective strategy is delivered to modulate the 2D/3D microstructure of tin-perovskite films by introduction of a 2D phase with the function of FPEABr, which induces high-orientation growth of 3D FASnI₃ by embracing the 3D grains at their surfaces and boundaries. That leads to a breakthrough of device performance of 14.81% in power conversion efficiency, along with 14.03% certified.

Abstract

As the most promising lead-free one, tin-halides based perovskite solar cells still suffer from the severe bulk-defect due to the easy oxidation of tin from divalent to tetravalent. Here, a general and effective strategy is delivered to modulate the microstructure of 2D/3D heterogeneous tin-perovskite absorber films by substituting FAI with FPEABr in FASnI₃. The introduction of 2D phase can induce highly oriented growth of 3D FASnI₃ and it is revealed in the optimal 2D/3D film that 2D phase embraces 3D grains and locates at the surfaces and grain boundaries. The FPEA⁺ based 2D tin-perovskite capping layer can offer a reducing atmosphere for vulnerable 3D FASnI₃ grains. The unique microstructure effectively suppresses the well-known oxidation from Sn²⁺ to Sn⁴⁺, as well as decreasing defect density, which leads to a remarkable enhanced device performance from 9.38% to 14.81% in conversion efficiency. The certified conversion efficiency of 14.03% announces a new record and moves a remarkable step from the last one (12.4%). Besides of this breakthrough, this work definitely paves a new way to fabricate high-quality tin-perovskite absorber film by constructing effective 2D/3D microstructures.

Three 2,6-diphenylpyridine-3,5-dicarbonitrile-based compounds with excellent photoluminescent quantum yields (79–100%) and high horizontal dipole ratios (86−88%) in the thin films are demonstrated. With two methyl groups on the triarylamines, the spin−orbit coupling is enhanced due to the elevated locally excited triplet states (³LE), leading to a fast reverse intersystem crossing. Green thermally activated delayed fluorescence (TADF) organic light-emitting diodes based on them exhibit a record-high external quantum efficiency of 39.8% without any optical extraction technique.

Abstract

Highly efficient thermally activated delayed fluorescence (TADF) molecules are in urgent demand for solid-state lighting and full-color displays. Here, the design and synthesis of three triarylamine-pyridine-carbonitrile-based TADF compounds, TPAPPC, TPAmPPC, and tTPAmPPC, are shown. They exhibit excellent photoluminescence quantum yields of 79−100% with small ΔE _ST values, fast reverse intersystem crossing (RISC), and high horizontal dipole ratios (Θ_// = 86−88%) in the thin films leading to the enhancement of device light outcoupling. Consequently, a green organic light-emitting diode (OLED) based on TPAmPPC shows a high average external quantum efficiency of 38.8 ± 0.6%, a current efficiency of 130.1 ± 2.1 cd A^–1, and a power efficiency of 136.3 ± 2.2 lm W^–1. The highest device efficiency of 39.8% appears to be record-breaking among TADF-based OLEDs to date. In addition, the TPAmPPC-based device shows superior operation lifetime and high-temperature resistance. It is worth noting that the TPA-PPC-based materials have excellent optical properties and the potential for making them strong candidates for TADF practical application.

Flexible and stretchable solar cells are important for a range of emerging applications such as electronic skins, e-textiles, wearable displays and health sensors, among others. An overview of stretchable optoelectronics is provided, where the benefits of stretchable solar cells are addressed, and the progress made in this field in terms of efficiency and strategies to achieve mechanical stretchability are underlined.

Abstract

Emerging forms of soft, flexible, and stretchable electronics promise to revolutionize the electronics industries of the future offering radically new products that combine multiple functionalities, including power generation, with arbitrary form factor. For example, skin-like electronics promise to transform the human-machine-interface, but the softness of the skin is incompatible with traditional electronic components. To address this issue, new strategies toward soft and wearable electronic systems are currently being pursued, which also include stretchable photovoltaics as self-powering systems for use in autonomous and stretchable electronics of the future. Here recent developments in the field of stretchable photovoltaics are reviewed and their potential for various emerging applications are examined. Emphasis is placed on the different strategies to induce stretchability including extrinsic and intrinsic approaches. In the former case, engineering and patterning of the materials and devices are key elements while intrinsically stretchable systems rely on mechanically compliant materials such as elastomers and organic conjugated polymers. The result is a review article that provides a comprehensive summary of the progress to date in the field of stretchable solar cells from the nanoscale to macroscopic functional devices. The article is concluded by discussing the emerging trends and future developments.

A high-performance self-powered photodetector based on a 2D Ruddlesden–Popper perovskite with an ordered phase distribution is presented. The increased built-in potential due to the gradient phase distribution, oriented crystals, and improved crystal quality jointly contribute to the high photoresponse of the device in the entire response spectrum range.

Abstract

2D Ruddlesden–Popper perovskites exhibit great potential in optoelectronic devices for superior stability compared with their 3D counterparts. However, to achieve a high level of device performance, it is crucial but challenging to regulate the phase distribution of 2D perovskites to facilitate charge carrier transfer. Herein, using a solvent additive method (adding a small amount of dimethyl sulfoxide (DMSO) in N,N-dimethylformamide (DMF)) combined with a hot-casting process, the phase distribution of (PEA)₂MA₃Pb₄I₁₃ (PEA⁺ = C₆H₅CH₂CH₂NH₃ ⁺, MA⁺ = CH₃NH₃ ⁺) perovskite can be well controlled and the Fermi level of perovskites along the film thickness direction can achieve gradient distribution. The increased built-in potential, oriented crystal, and improved crystal quality jointly contribute to the high photoresponse of devices in the entire response spectrum range. The optimum device exhibits a characteristic detection peak at 570 nm with large responsivity/detectivity (0.44 A W⁻¹/3.38 × 10¹² Jones), ultrafast response speed with a rise/fall time of 20.8/20.6 µs, and improved stability. This work suggests the possibility of manipulating the ordered phase distribution of 2D perovskites toward high-performance and stable optoelectronic conversion devices.

A hydrophobic p-type semiconducting additive, fluorinated-gold-clusters, is used as a bifunctional interfacial mediator to efficiently modulate the carrier dynamics of perovskite and restrain the perovskite from degradation by external environmental stimuli, which results in an n–i–p perovskite solar cell with a champion efficiency up to 24.02% and moisture stability over 10 000 h in relative humidity of 75%.

Abstract

Tackling the interfacial loss in emerged perovskite-based solar cells (PSCs) to address synchronously the carrier dynamics and the environmental stability, has been of fundamental and viable importance, while technological hurdles remain in not only creating such interfacial mediator, but the subsequent interfacial embedding in the active layer. This article reports a strategy of interfacial embedding of hydrophobic fluorinated-gold-clusters (FGCs) for highly efficient and stable PSCs. The p-type semiconducting feature enables the FGC efficient interfacial mediator to improve the carrier dynamics by reducing the interfacial carrier transfer barrier and boosting the charge extraction at grain boundaries. The hydrophobic tails of the gold clusters and the hydrogen bonding between fluorine groups and perovskite favor the enhancement of environmental stability. Benefiting from these merits, highly efficient formamidinium lead iodide PSCs (champion efficiency up to 24.02%) with enhanced phase stability under varied relative humidity (RH) from 40% to 95%, as well as highly efficient mixed-cation PSCs with moisture stability (RH of 75%) over 10 000 h are achieved. It is thus inspiring to advance the development of highly efficient and stable PSCs via interfacial embedding laser-generated additives for improved charge transfer/extraction and environmental stability.

Nature Communications, Published online: 22 July 2021; doi:10.1038/s41467-021-24762-w

Electric field induced ion migration is a well-known phenomenon in perovskite, but the consequences are notorious, and thus needs to be prevented. Here, on the other hand, the authors cleverly manipulate this event for realising resistive random-access memory and light-emitting electrochemical cell in one device based on CsPbBr3 quantum dots.