Chen Weijie

Stable and efficient perovskite solar cells (PSCs) are achieved via introducing PbPyA₂ as an additive. Benefiting from the strong interaction, incorporating PbPyA₂ can lower the defects, suppress ion migration and component volatilization of perovskite, resulting in great improvements in heat and humidity tolerance. More importantly, the resulting PSC maintains 93% of initial efficiency after maximum power point tracking for 540 h.

Abstract

Stability has become the main obstacle for the commercialization of perovskite solar cells (PSCs) despite the impressive power conversion efficiency (PCE). Poor crystallization and ion migration of perovskite are the major origins of its degradation under working condition. Here, high‐performance PSCs incorporated with pyridine‐2‐carboxylic lead salt (PbPyA₂) are fabricated. The pyridine and carboxyl groups on PbPyA₂ can not only control crystallization but also passivate grain boundaries (GBs), which result in the high‐quality perovskite film with larger grains and fewer defects. In addition, the strong interaction among the hydrophobic PbPyA₂ molecules and perovskite GBs acts as barriers to ion migration and component volatilization when exposed to external stresses. Consequently, superior optoelectronic perovskite films with improved thermal and moisture stability are obtained. The resulting device shows a champion efficiency of 19.96% with negligible hysteresis. Furthermore, thermal (90 °C) and moisture (RH 40–60%) stability are improved threefold, maintaining 80% of initial efficiency after aging for 480 h. More importantly, the doped device exhibits extraordinary improvement of operational stability and remains 93% of initial efficiency under maximum power point (MPP) tracking for 540 h.

An interconnected SnO₂ thin film (composed of presynthesized SnO₂ nanocrystals interconnected by amorphous phase SnO _x ) is proposed as an electron transport layer for efficient flexible perovskite solar cells. The interconnected SnO₂ thin film enables fast electron extraction from the perovskite layer and retards nonradiative charge carrier recombination. Corresponding flexible solar cells demonstrate a power conversion efficiency as high as 16.29%.

This study reports on interconnected SnO₂ electron transport layers (composed of presynthesized SnO₂ nanocrystals interconnected by amorphous phase SnO _x ) processed at low temperature (120 °C) for highly efficient flexible perovskite solar cells. Herein, the amorphous phase SnO _x serves as an effective binder to connect the SnO₂ nanocrystals to obtain ultra‐smooth electron transport layers. Further characterization of the charge carrier kinetics at the perovskite/electron transport layer interface confirms that the interconnected SnO₂ nanocrystals layer facilitates electron extraction and retards nonradiative charge carrier recombination. Consequently, a power conversion efficiency of 16.29% is achieved for flexible perovskite solar cells using the interconnected SnO₂ electron transport layer on indium tin oxide/polyethylene terephthalate substrates.

A simple coalloying strategy is applied to partly substitute HC(NH₂)₂/CH₃NH₃ (FA/MA) and I⁻ in FA_0.85MA_0.15PbI₃ perovskite by Cs⁺ and Ac⁻ respectively, which is an effective way to improve the tolerance factor, crystallinity, electronic properties, and band structure of FA_0.85MA_0.15PbI₃ materials. Consequently, the coalloyed perovskite solar cells yield a champion power conversion efficiency of 21.95% with negligible hysteresis and high stability.

A simple coalloying strategy is applied to improve the efficiency and stability of FA_0.85MA_0.15PbI₃ perovskite solar cells (PSCs) by using cesium acetate (CsAc) as an additive. It is found that the simultaneous incorporation of cation (Cs⁺) and anion (Ac⁻) into the FA_0.85MA_0.15PbI₃ film is an effective approach to realize lattice contraction, grain size enlargement, photoelectric properties improvement, band structure modulation, and therefore the optimization of the efficiency and stability of PSCs. At optimal CsAc alloying, the FA_0.85MA_0.15PbI₃ PSCs achieve a maximum power conversion efficiency (PCE) of 21.95% and an average of over 21%. In addition, the alloyed PSCs retain 97% of their initial PCE values after aging for 55 days in air without encapsulation.

Though great success has been achieved in perovskite solar cells (PSCs), it still suffers from several drawbacks in terms of stability and higher efficiency. Doping as effective method to modify the optical and electronic properties of the materials has been hotly studied in lead halide perovskites (LHPs). In this mini review, we discuss the Pb‐site doping in organic‐inorganic hybrid perovskites (OIH‐LHPs) and inorganic CsPbX₃ based materials. We conclude the doping has three functions toward PSCs: participating in crystalline process, modifying the energy states in LHPs and acting important role on the stability of PSCs. Issues about further improvements are raised and perspectives for further investigation are presented at last.

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The large grains and high crystallinity of Pb(Ac)₂‐doped α‐CsPbI₂Br active layers with CsBr passivation is realized by a two‐step annealing process. The corresponding planar all‐inorganic CsPbI₂Br perovskite solar cells exhibit a long‐term ultrahigh power conversion efficiency of 16.37%, with a substantially improved V _OC of 1.271 V.

All‐inorganic CsPbI₂Br perovskite has attracted increasing attention, owing to its outstanding thermal stability and suitable bandgap for optoelectronic devices. However, the substandard power conversion efficiency (PCE) and large energy loss (E _loss) of CsPbI₂Br perovskite solar cells (PSCs) caused by the low quality and high trap density of perovskite films still limit the application of devices. Herein, the post‐treatment of evaporating cesium bromide (CsBr) is utilized on top of the perovskite surface to passivate the CsPbI₂Br–hole‐transporting layer interface and reduce E _loss. The results of microzone photoluminescence indicate that the evaporated CsBr gathered at the grain boundaries of CsPbI₂Br layers and Br‐enriched perovskites (CsPbI _x Br_3−x , x < 2) are formed, which can provide protection for CsPbI₂Br. Therefore, the gaps between crystal grains are filled up, and the recombination loss of the all‐inorganic CsPbI₂Br PSCs is reduced accordingly. The champion device exhibits high open‐circuit voltage and a PCE of 1.271 V and 16.37%, respectively. This is the highest reported PCE among all‐inorganic CsPbI₂Br PSCs reported so far. In addition, the stability of CsPbI₂Br PSCs is effectively improved by CsBr passivation, and the device without encapsulation can retain 86% of its initial PCE after 1368 h of storage, which is beneficial for practical applications.

Here, studies on regulation of the interfacial charge balance in SnO₂‐based planar perovskite solar cells are reported. SnO₂ with optimum thickness exhibits enhanced charge balance. Moreover, trap‐assisted carrier recombination is significantly suppressed by using diethylenetriaminepentaacetic acid as a passivator. As a result, the champion device demonstrates a promising efficiency of 21.28% with negligible hysteresis and much improved environmental stability.

Control of dynamics at the electron transport layer–perovskite interface, such as charge transfer and recombination, is essential in achieving high‐efficiency planar perovskite solar cells (PSCs). Herein, it was observed that the trade‐off between unfavorable electron transport of a thick SnO₂ film and serious electron recombination at thin SnO₂ film/perovskite interfaces is essential for the performance of SnO₂‐based planar PSCs. The optimized efficiency of devices beyond 20% is obtained by using a two‐step deposition of SnO₂. Moreover, trap‐assisted carrier recombination is significantly suppressed by using the diethylenetriaminepentaacetic acid passivator via the formation of coordination with undercoordinated Sn and Pb²⁺ ions. As a result, the champion device demonstrates a promising efficiency of 21.28% with negligible hysteresis and much improved environmental stability, i.e., retaining 98% of the initial efficiency under ambient atmosphere over 1000 h.

Carbon‐electrode based perovskite solar cells (CPSCs) are well known for their low cost and sound stability. However, the highest power conversion efficiency of these devices is only about 70% of that demonstrated by metal electrode‐based PSCs, leaving a gap of about 30%. Bulk engineering and interface engineering is helpful in narrowing the gap. Herein, these two strategies are summarized for CPSCs.

Carbon electrodes have been adopted widely in perovskite solar cells (PSCs). Due to its suitable work function (though not high enough), the carbon electrode itself could extract photogenerated holes and has helped to achieve a power conversion efficiency of ≈16% in the absence of hole‐transporting material. Meanwhile, due to the inert chemical nature and the micrometer‐sized film thickness (≈10 μm), carbon electrodes can prolong the stability of PSCs. These merits are appealing for the commercialization of PSCs. However, the efficiency of carbon‐electrode PSCs is relatively low. A gap of ≈30% remains when comparing with PSCs using evaporated metal films as the electrode. Herein, the progresses in the efficiency of the four kinds of carbon‐electrode based PSCs (mesoscopic, embedment, planar, and quasi‐planar) are reviewed and compared to metal‐electrode based PSCs. Then, the role of bulk engineering and interface engineering in the progress of efficiency is discussed. Finally, outlooks are described in accordance with the discussions.

Bi₂Te₃ nanoplates with a tunable energy structure are introduced in inorganic perovskite solar cells (PSCs), accelerating hole transport by the matched band alignment. Confirmed by systematic measurements, charge recombination is largely suppressed due to lower trap density and higher carrier mobility. The optimal PSC with Bi₂Te₃ exhibits highly decreased V _OC loss and enhanced long‐term stability over 50 days.

To solve the thermal instability issue of organic–inorganic hybrid perovskites, all‐inorganic perovskite solar cells (PSCs) have been featured in the spotlight. However, their power conversion efficiencies (PCEs) are far from satisfactory due to the substantially radiative and nonradiative recombination of charge carriers in the common‐structured devices. Herein, bismuth telluride (Bi₂Te₃) nanoplates are designed as an interlayer between cesium lead halide (CsPbBrI₂) and 2,2′,7,7′‐tetrakis(N,N‐di‐p‐methoxyphenylamine)‐9,90‐spirobifluorene (Spiro‐OMeTAD) to reduce the notorious trap states and charge recombination. Confirmed by systematic electrochemical and photoelectrical techniques, the Bi₂Te₃ interlayer optimizes hole extraction and transport efficiency because of the matched band level structure and drastically reduces trap defect densities. Prolonged effective lifetime and shorter diffusion time induced by the Bi₂Te₃ interlayer reveal less electron–hole recombination and more efficient carrier transport, which lead to a larger photocurrent and less open circuit voltage loss of PSCs. The all‐inorganic PSCs with the optimal Bi₂Te₃ interlayer exhibit a highly enhanced PCE of 11.96%. Moreover, Bi₂Te₃ also acts as a blocking layer for the migration of iodide ions, silver, and moisture, resulting in a considerable device stability of more than 70% of initial PCE after 50 days without extra encapsulation. This low‐cost and facile method for efficient and stable all‐inorganic PSCs offers great promise as a next‐generation renewable energy source.

Sn‐based perovskite solar cells (PSCs) with 6.33% power conversion efficiency are fabricated with an aperture area of 1 cm² by introducing a post‐deposition vapor annealing method. The fabricated Sn‐based PSCs show promising stability, both under dark and maximum power‐point tracking conditions.

Sn‐based perovskite solar cells (PSCs) are promising alternatives to replacing toxic Pb‐based PSCs, which have shown a rapid rise in photovoltaic applications in the past 1 year. However, the reported Sn‐based PSCs are often fabricated with a small aperture area (typically 0.02–0.1 cm²) because forming homogeneous pinhole‐free continuous films over a large surface area is still challenging. Herein, a post‐deposition vapor annealing (PDVA) process assisted by methylammonium chloride vapor is presented that enables the fabrication of stable, homogeneous pinhole‐free FASnI₃ perovskite absorber films with low crystal defects and low surface recombination over a relatively large area up to 1.02 cm². Inverted planar solar cells fabricated with a 1.02 cm² aperture area show a maximum power conversion efficiency of 6.33% with high reproducibility and stability. The shelf‐lifetime stability test shows that the PSCs retain 90% of their performance for more than 1000 h when stored in a N₂‐filled glove box and under dark conditions. The preliminary light‐soaking stability tests under continuous illumination and maximum power‐tracking conditions are relatively promising. This study marks an important step toward the up scaling of Sn‐based PSCs.

2D/3D perovskite heterostructures or composites have recently been recognized as efficient strategy to improve the stability of perovskite solar cells. In this work, we demonstrated a novel solution process to develop 2D/3D perovskites with modulated diffusion passivation by introducing phenylethylammonium iodide (PEAI) and N,N‐dimethylformamide (DMF) additive, which could effectively enhance device performance and long‐term stability. Compared with conventional device, the device with PEAI and DMF solvent additive treatment exhibited enhanced charge transport, improved charge extraction and suppressed non‐radiative carrier recombination. The solar cells with an optimal 2D/3D perovskite passivation treatment exhibited an extremely high fill factor of 83.6% and an average power conversion efficiency of 21.4% (21.3% by using integrated photocurrent from IPCE spectra) based on NiO_x hole transport layer. Furthermore, the unencapsulated device exhibited excellent stability under continuously simulated sunlight illumination and outstanding air stability after 1000 h storage under ambient air condition.

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In article no. 1900125, Guokun Ma, Hao Wang, and co‐workers use liquid crystal (LC) molecule (4'‐heptyl‐4‐biphenylcarbonitrile) as a binding agent to connect the grain boundaries of perovskites. After treatment with the LC, perovskite crystal growth orientation can be controlled and the electron transport process is accelerated. Remarkably, the LC greatly contributes to the environmental stability of the devices.

Black phosphorus quantum dots (BPQDs)‐assisted growth of a perovskite film is reported. Serving as heterogeneous nucleation centers, the BPQDs assist in the crystallization of the perovskite film, achieving perovskite films with higher crystallinity and less defects. Consequently, the perovskite solar cells made with BPQDs achieve a maximum power conversion efficiency of 20% and an encouraging improved thermal stability.

Crystallinity and trap‐state density of a perovskite film play a critical role in the performance of corresponding perovskite solar cells (PVSCs). Herein, liquid‐phase‐exfoliated black phosphorus quantum dots (BPQDs) are incorporated into the perovskite precursor solution as additives to direct the formation of the perovskite film, i.e., methylammonium lead iodide (MAPbI₃). It is found that the perovskite films made with BPQDs have higher crystallinity and less nonradiative detects compared with the pristine ones, leading to longer carrier lifetime and higher carrier collection efficiency. Time‐of‐flight secondary‐ion mass spectra and surface density calculation of BPQDs reveal that the improvement of the perovskite film quality may be related to the heterogeneous nucleation of the perovskite film at the BPQDs. PVSCs using MAPbI₃ films made with BPQDs achieve a maximum power conversion efficiency of 20.0% and an encouraging thermal stability of T ₈₀ = 100 h at 100 °C. Both values are remarkably higher than the devices with pristine perovskite films. Therefore, this work demonstrates the potential of the 2D materials quantum dots‐assisted growth method for high‐performance PVSCs.

CdSe/ZnS quantum dots (QDs) are used as the cathode interlayer (CIL) modifier to enhance the power conversion efficiency of organic solar cells (OSCs) from 13.0% to 14.6% by improving the open‐circuit voltage (V _oc) and short‐circuit current density (J _sc). The highest reported performance in QD‐modified OSCs is achieved.

Interfacial engineering plays an important role to improve the photovoltaic performance of organic solar cells (OSCs). Herein, CdSe/ZnS quantum dots (QDs) are used as a cathode interlayer (CIL) modifier. By using this strategy, an enhanced power conversion efficiency (PCE) from 13.0% to 14.6% is achieved, mainly due to the increase in open‐circuit voltage (V _oc) and short‐circuit current density (J _sc). A single QD layer of a proper size can reduce the defects on the surface of the active layer and smoothen the interface between the active layer and cathode. Furthermore, the low work function of the QDs with dipole moment facilitates charge transport and suppresses charge recombination at the interface by strengthening the built‐in field, thus contributing to the enhancement of PCE. The excitons generated by the QDs can also be dissociated at the IT‐4F/QD interface, which boosts the photon harvesting capability of the device. As a result, a high PCE of 14.6% is achieved for QD‐modified OSCs.

Propane‐1,3‐diammonium cations are first adopted to construct cesium–formamidinium (Cs–FA) perovskite solar cells (PSCs) with an efficiency of 18.1% and much enhanced device stability, and the opposing effects induced by the diammonium cation are resolved.

Incorporating diammonium cations, which electrostatically connect the adjacent inorganic slabs ([PbI₆]⁴⁻), into 3D perovskite is recently proposed to develop high‐performance perovskite solar cells (PSCs). However, due to limited studies, the effects of these organic cations on the perovskite structural and optoelectronic properties are yet to be understood. Herein, a diammonium cation, propane‐1,3‐diammonium (PDA), is first proposed to modulate the cesium–formamidinium (Cs–FA)‐mixed cation perovskite. By increasing the PDA content, the efficiency of the Cs_0.15FA_{0.85 − x} PDA _x PbI₃ PSC first increases and then drastically decreases. The highest power conversion efficiency (PCE) of 18.10% obtained by Cs_0.15FA_0.83PDA_0.02PbI₃ is superior to that of the Cs_0.15FA_0.85PbI₃ (16.82%). Through systematic investigations, it is revealed that the PDA content–dependent efficiency is attributed to a competition between the enhanced defect passivation and emerged excitonic effect with an increased PDA content. Moreover, the encapsulated Cs_0.15FA_0.83PDA_0.02PbI₃ device exhibits almost 1.5 times increased stability than the Cs_0.15FA_0.85PbI₃ counterpart, with 83% of its initial efficiency retained after 500 h exposure, under continuous light soaking at 60 °C in ambient air. This study provides a practical strategy to enhance the device stability without sacrificing the efficiency and deepens our understanding on effects of diammonium cation incorporated in 3D perovskite.

A polymer solar cell (PSC) with a large active area of 216 cm² and high power conversion efficiency of 7.7% is presented, involving a nonfullerene acceptor and the solution‐processable ZrOx interfacial layer made by blade coating. This represents the highest reported efficiency for PSCs with an active area more than 10 cm². More encouragingly, the large‐area PSC shows good long‐term thermal stability as well.

A polymer solar cell involving a nonfullerene acceptor is made by blade coating. In the ternary bulk‐heterojunction layer, the donor is 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‐thiophene‐2‐yl)‐ 5,7‐bis(2‐ethylhexyl)benzo[1,2‐c:4,5‐c’]dithiophene‐4,8‐dione)] (PBDB‐T) and the acceptor is a mixture of 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) and [6,6]‐phenyl C₇₁‐butyric acid methyl ester (PC₇₁BM). The device structure is an indium tin oxide (ITO)‐coated glass substrate/PEDOT:PSS/ternary active layer/interfacial layer/Al. For a small active area of 0.04 cm², the best power conversion efficiency is 9.8% with the LiF interfacial layer. For a large active area of 216 cm², the best efficiency is 7.7% with the ZrOx interfacial layer. After annealing at 85 °C for 30 days, the large‐area device keeps 75% of the initial efficiency. The efficiency of 4.9% is achieved for a large‐area semi‐transparent device.

A versatile alkaline earth metals doping strategy is utilized to engineer the electronic structure of NiO _x contacts for inverted planar perovskite solar cells, which demonstrates a power conversion efficiency of 19.49% with a high open‐circuit voltage of 1.14 V. Enhanced charge extraction and conductivity are responsible for the high‐performance devices.

Organometallic halide perovskite solar cells (PSCs) are rapidly evolving as the promising photovoltaic technologies with high record efficiency over 24%. The inorganic p‐type semiconductor NiO _x is extensively used as important hole transport layers for the realization of stable and hysteresis‐free solar cells due to their good electronic properties, facile fabrication, and excellent chemical endurance. However, the critical issues of NiO _x films including poor intrinsic conductivity and mismatched band alignment limit further improvement of the device performance. Herein, it is demonstrated that a versatile alkaline earth metal (Mg, Ca, Sr, and Ba) doping strategy can effectively engineer the electronic properties of NiO _x contacts in inverted planar PSCs. Alkaline earth metal doping can deepen valence band maximum and enhance the hole conductivity of NiO _x films, which better aligns the energy band in solar cells. The champion device based on Sr‐doped NiO _x films attains a power conversion efficiency of 19.49% with a high open‐circuit voltage (V _OC) of 1.14 V for NiO _x ‐based CH₃NH₃PbI₃ devices. The resulted device shows negligible hysteresis and high stability as well. This finding provides a systematic doping strategy to further improve the performance of inverted planar PSCs.

Herein, the open‐circuit voltage losses and bias‐dependent photo‐ and electroluminescence of high‐performance 2D/3D perovskite solar cells, which exhibit outstanding optoelectronic properties, are investigated. These are state‐of‐the‐art photovoltaic devices. Results suggest that by reducing nonradiative recombination processes in the absorber, the power conversion efficiency of the studied photovoltaic devices can be improved.

Herein, the optoelectronic properties of interface‐engineered perovskite 2D|3D‐heterojunction structure solar cells are reported. The reciprocity theorem is applied to determine the maximum open‐circuit voltage (V _oc) the device can deliver under solar illumination. A V _oc of 1.295 V is found, analyzing the measured external quantum efficiency and assuming only radiative recombination. For comparison, the experimental open‐circuit voltage found for the studied 2D|3D heterojunctions is 1.15 V. The contribution of nonradiative recombination is explored by measuring the electroluminescence quantum yield. A quantum yield of 0.4% is found at current densities equivalent to 1 sun illumination. This translates into a V _oc loss of ≈140 mV, which is in very good agreement with the experimental findings. In addition, the fundamental correlation between luminescence intensity and the chemical potential predicted by the generalized Planck law is confirmed for the photoluminescence measured at different light intensities when the device is operated under open‐circuit conditions and for the electroluminescence when operated under a forward bias. The investigations in this study suggest that further efficiency improvements can be achieved by reducing the nonradiative recombination in the studied solar cell. At the same time, a high‐performance near IR light emitting diode can be realized.

A liquid crystal (LC) molecule (4′‐heptyl‐4‐biphenylcarbonitrile) is first used as a “binding agent” to connect grain boundaries of perovskite. The crystal orientation of perovskite grains is controlled and the electron transport process is accelerated after treating with LC; these are reflected by the significant improvement in power conversion efficiency and high fill factor. Remarkably, the LC greatly contributes to the humid‐stability of perovskite solar cells.

Hybrid perovskites have rapidly emerged as highly promising optoelectronic materials for perovskite solar cells (PSCs), whereas solution‐processed perovskite films usually contain a large amount of grain‐boundary network, which is unbeneficial for efficient film function, including charge transport and environmental stability. Herein, a liquid crystal (LC) molecule is first used as a “binding agent” to connect grains and fill grain boundaries of perovskite. The LC molecule (4′‐heptyl‐4‐biphenylcarbonitrile) interacts with PbI₂ to control the crystal orientation for fine and oriented perovskite grains, which accelerates electron transport and enhances environmental stability. Consequently, compared with the pristine devices, the power conversion efficiency of the LC‐based device increases from 17.14% to 20.19% with a high fill factor (over 80%). Remarkably, the LC‐based PSCs retain 92% of their initial efficiency at 25 °C, and a relative humidity of 70% after 500 h, whereas the control samples are almost degraded completely under the same conditions.

The fabrication of efficient organic solar cells (OSCs) via the combination of one‐step doctor‐blade printing and solvent vapor annealing (SVA) is reported for the first time. SVA improves the spontaneous stratification of the interlayer between the active layer and electrode. The achieved efficiency of 11.14% is among the highest reported to date for doctor‐blade‐coated OSCs.

A pronounced enhancement of the power conversion efficiency (PCE) by 38% is achieved in one‐step doctor‐blade printing organic solar cells (OSCs) via a simple solvent vapor annealing (SVA) step. The organic blend composed of a donor polymer, a nonfullerene acceptor, and an interfacial layer (IL) molecular component is found to phase‐separate vertically when exposed to a solvent vapor‐saturated atmosphere. Remarkably, the spontaneous formation of a fine, self‐organized IL between the bulk heterojunction (BHJ) layer and the indium tin oxide (ITO) electrode facilitated by SVA yields solar cells with a significantly higher PCE (11.14%) than in control devices (8.05%) without SVA and in devices (10.06%) made with the more complex two‐step doctor‐blade printing method. The stratified nature of the ITO/IL/BHJ/cathode is corroborated by a range of complementary characterization techniques including surface energy, cross‐sectional scanning electron microscopy, grazing incidence wide angle X‐ray scattering, and X‐ray photoelectron spectroscopy. This study demonstrates that a spontaneously formed IL with SVA treatment combines simplicity and precision with high device performance, thus making it attractive for large‐area manufacturing of next‐generation OSCs.

An ingenious surface chlorination treatment method is used to passivate the interface defects of perovskite/zinc oxide (ZnO), which effectively reduces the interface charge recombination loss and improves the poor interface chemical characteristics. Thus, the fabricated zinc oxide–chlorine (ZnO–Cl)‐based device achieves an enhanced efficiency and suppressed hysteresis, as well as strengthened stability in perovskite solar cells.

Defect states on the zinc oxide (ZnO) surface cause severe interfacial charge recombination and perovskite decomposition during device operation, which inevitably leads to efficiency loss and poor device stability, making the usage of ZnO in perovskite solar cells (PSCs) problematic. Herein, a simple and effective method of inorganic chlorination treatment is used to passivate the surface defects of the ZnO electron transport layer. It is shown that chlorine (Cl) effectively fills the oxygen vacancy defects of ZnO, suppressing charge recombination and facilitating charge transport at the perovskite/ZnO interface. Therefore, the resulting CH₃NH₃PbI₃‐based device achieves an enhanced power conversion efficiency with suppressed hysteresis. Meanwhile, the chlorination of the ZnO surface protects the perovskite layer from decomposition, thus improving device stability. Herein, an ingenious method is developed to further improve the device performance of ZnO‐based PSCs and useful guidance is provided for the development of other perovskite optoelectronics, especially those with ZnO as the charge transport layer.

Various strategies related to light management and photocarrier collection are developed to enhance perovskite solar cell performance. The exploration of novel plasmonic nanostructures with predesigned size and shape is needed in the field. Herein, a bioinspired nanostructure of Au nanorod–nanoparticle dimers with structural darkness is used to enhance the light harvesting and performance of perovskite solar cells.

Hybrid perovskites have recently attracted enormous attention for photovoltaic applications, and various strategies related to light management and photocarrier collection are developed to enhance their performance. As an effective route toward near‐field light enhancement, metal nanostructures with subwavelength dimensions can couple incident photons with conduction electrons, giving rise to localized surface plasmon resonances. However, efficiency enhancements through plasmonic routes are limited to the short wavelength range corresponding to metal extinction wavelength. Thus, the exploration of novel plasmonic nanostructures with predesigned sizes and shapes is needed to advance this field. Herein, for the first time, a bioinspired nanostructure of Au nanorod–nanoparticle dimers with structural darkness is exploited to enhance the light harvesting and performance of perovskite solar cells. Differing from conventional metallic nanoparticles, biometric nanoparticles introduce geometric singularity to the system, providing a broadband response for energy harvesting. By embedding the core–shell gold dimers in the perovskite solar cells, a notable enhancement of broadband light absorption is observed, and sequentially, the efficiency of perovskite solar cells increases by 16%.

The alcohol vapor post‐annealing treatment on Sb₂S₃ films is demonstrated as an effective method for high‐performance Sb₂S₃ planar heterojunction solar cells. Due to the higher polarity of methanol compared with that of ethanol and isopropanol, the meth‐annealed Sb₂S₃ devices show a power conversion efficiency of 5.27%, with an increase in 31% compared with the control device.

Solution‐processed Sb₂S₃ planar heterojunction solar cells have shown great progress in power conversion efficiency (PCE) in recent years. However, a conventional solution process yields Sb₂S₃ films with a small grain size. Herein, an alcohol vapor post‐annealing strategy is reported that uses alcohol vapors to facilitate grain growth of Sb₂S₃ films during annealing, achieving films with a larger grain size and better crystallinity. A series of alcohols with different polarities are used for the vapor post‐annealing. Methanol with the highest polarity provides films with the largest grain size. As a result, the Sb₂S₃ films prepared via vapor post‐annealing show enhanced light absorption, longer carrier lifetime, and less carrier recombination, which are verified by photoluminescence, transient photovoltage, suns‐short‐circuit photocurrent density, and suns‐open‐circuit voltage measurements. The Sb₂S₃ solar cells post‐annealed with methanol vapor exhibit a PCE of 5.27%, showing a drastic improvement of 31% compared with the non‐treated devices. The alcohol vapor post‐annealing approach presents a new avenue toward controlling the morphology and crystallinity of solution‐processed Sb₂S₃ films and achieving efficient Sb₂S₃ solar cells.

Eco‐compatible solvent‐processed organic photovoltaic cells with over 16% power conversion efficiency are achieved via modifying the flexible alkyl chains of BTP‐4F‐8. Combining with the polymer donor T1, over 14% power conversion efficiencies are obtained not only for using several kinds of greener solvents like o‐xylene, 1,2,4‐trimethylbenzene, and tetrahydrofuran but also for 1.07 cm² cells by the blade‐coating method.

Abstract

Recent advances in nonfullerene acceptors (NFAs) have enabled the rapid increase in power conversion efficiencies (PCEs) of organic photovoltaic (OPV) cells. However, this progress is achieved using highly toxic solvents, which are not suitable for the scalable large‐area processing method, becoming one of the biggest factors hindering the mass production and commercial applications of OPVs. Therefore, it is of great importance to get good eco‐compatible processability when designing efficient OPV materials. Here, to achieve high efficiency and good processability of the NFAs in eco‐compatible solvents, the flexible alkyl chains of the highly efficient NFA BTP‐4F‐8 (also known as Y6) are modified and BTP‐4F‐12 is synthesized. Combining with the polymer donor PBDB‐TF, BTP‐4F‐12 shows the best PCE of 16.4%. Importantly, when the polymer donor PBDB‐TF is replaced by T1 with better solubility, various eco‐compatible solvents can be applied to fabricate OPV cells. Finally, over 14% efficiency is obtained with tetrahydrofuran (THF) as the processing solvent for 1.07 cm² OPV cells by the blade‐coating method. These results indicate that the simple modification of the side chain can be used to tune the processability of active layer materials and thus make it more applicable for the mass production with environmentally benign solvents.

Nonconjugated multi‐zwitterionic small‐molecule electrolyte (NSE) molecules in perovskite solar cells (PSCs) act not only as both charge‐extracting layers for barrier‐free cathode charge collection but also as charged defect fillers in perovskite bulk and interfaces by spontaneous bottom‐up passivation. Thus, the NSE‐based PSCs deliver PCEs as high as 21.18% with an ultrahigh V _OC of 1.19 V, suppressed hysteresis, and enhanced stability.

Abstract

Recent perovskite solar cell (PSC) advances have pursued strategies for reducing interfacial energetic mismatches to mitigate energy losses, as well as to minimize interfacial and bulk defects and ion vacancies to maximize charge transfer. Here nonconjugated multi‐zwitterionic small‐molecule electrolytes (NSEs) are introduced, which act not only as charge‐extracting layers for barrier‐free charge collection at planar triple cation PSC cathodes but also passivate charged defects at the perovskite bulk/interface via a spontaneous bottom‐up passivation effect. Implementing these synergistic properties affords NSE‐based planar PSCs that deliver a remarkable power conversion efficiency of 21.18% with a maximum V _OC = 1.19 V, in combination with suppressed hysteresis and enhanced environmental, thermal, and light‐soaking stability. Thus, this work demonstrates that the bottom‐up, simultaneous interfacial and bulk trap passivation using NSE modifiers is a promising strategy to overcome outstanding issues impeding further PSC advances.

Highly efficient photoluminescence (PL‐QY = 68%), amplified spontaneous emission, and low‐threshold lasing in thin films of cesium lead bromide at room temperature are shown. Importantly, the films are not based on nanocrystals or quantum dots but consist of extended continuous layers, that are formed upon recrystallization of as‐deposited layers by thermal imprint.

Abstract

Cesium lead halide perovskites are of interest for light‐emitting diodes and lasers. So far, thin‐films of CsPbX₃ have typically afforded very low photoluminescence quantum yields (PL‐QY < 20%) and amplified spontaneous emission (ASE) only at cryogenic temperatures, as defect related nonradiative recombination dominated at room temperature (RT). There is a current belief that, for efficient light emission from lead halide perovskites at RT, the charge carriers/excitons need to be confined on the nanometer scale, like in CsPbX₃ nanoparticles (NPs). Here, thin films of cesium lead bromide, which show a high PL‐QY of 68% and low‐threshold ASE at RT, are presented. As‐deposited layers are recrystallized by thermal imprint, which results in continuous films (100% coverage of the substrate), composed of large crystals with micrometer lateral extension. Using these layers, the first cesium lead bromide thin‐film distributed feedback and vertical cavity surface emitting lasers with ultralow threshold at RT that do not rely on the use of NPs are demonstrated. It is foreseen that these results will have a broader impact beyond perovskite lasers and will advise a revision of the paradigm that efficient light emission from CsPbX₃ perovskites can only be achieved with NPs.

A multipurpose interconnection layer for the fabrication of monolithic perovskite/silicon tandem solar cells with high power conversion efficiency is explored. The interconnection of independently processed silicon and perovskite subcells could be a simple add‐on lamination step, alleviating the common fabrication complexity of perovskite/silicon tandem devices.

Abstract

A multipurpose interconnection layer based on poly(3,4‐ethylenedioxythiophene) doped with poly(styrene sulfonate) (PEDOT:PSS), and d‐sorbitol for monolithic perovskite/silicon tandem solar cells is introduced. The interconnection of independently processed silicon and perovskite subcells is a simple add‐on lamination step, alleviating common fabrication complexities of tandem devices. It is demonstrated experimentally and theoretically that PEDOT:PSS is an ideal building block for manipulating the mechanical and electrical functionality of the charge recombination layer by controlling the microstructure on the nano‐ and mesoscale. It is elucidated that the optimal functionality of the recombination layer relies on a gradient in the d‐sorbitol dopant distribution that modulates the orientation of PEDOT across the PEDOT:PSS film. Using this modified PEDOT:PSS composite, a monolithic two‐terminal perovskite/silicon tandem solar cell with a steady‐state efficiency of 21.0%, a fill factor of 80.4%, and negligible open circuit voltage losses compared to single‐junction devices is shown. The versatility of this approach is further validated by presenting a laminated two‐terminal monolithic perovskite/organic tandem solar cell with 11.7% power conversion efficiency. It is envisioned that this lamination concept can be applied for the pairing of multiple photovoltaic and other thin film technologies, creating a universal platform that facilitates mass production of tandem devices with high efficiency.

A novel method to synthesize an electron‐rich building block cyclopentadithienothiophene (CDTT) via a facile aromatic extension strategy is demonstrated and a promising nonfullerene small molecule acceptor (CDTTIC) is synthesized. The CDTTIC‐based as‐cast single‐junction organic solar cells exhibit efficiencies over 11% with an ultrahigh current density.

Abstract

A new method to synthesize an electron‐rich building block cyclopentadithienothiophene (9H‐thieno‐[3,2‐b]thieno[2″,3″:4′,5′]thieno[2′,3′:3,4]cyclopenta[1,2‐d]thiophene, CDTT) via a facile aromatic extension strategy is reported. By combining CDTT with 1,1‐dicyanomethylene‐3‐indanone endgroups, a promising nonfullerene small molecule acceptor (CDTTIC) is prepared. As‐cast, single‐junction nonfullerene organic solar cells based on PFBDB‐T: CDTTIC blends exhibit very high short‐circuit currents up to 26.2 mA cm⁻² in combination with power conversion efficiencies over 11% without any additional processing treatments. The high photocurrent results from the near‐infrared absorption of the CDTTIC acceptor and the well‐intermixed blend morphology of polymer donor PFBDB‐T and CDTTIC. This work demonstrates a useful fused ring extension strategy and promising solar cell results, indicating the great potential of the CDTT derivatives as electron‐rich building blocks for constructing high‐performance small molecule acceptors in organic solar cells.

1,2,4‐triazole is a stable and efficient aromatic compound having triamine structure that can improve the bond strength and electronic properties of perovskite with the reduced carrier traps. Proper alloying of 1,2,4‐triazole greatly stabilizes triple‐cation perovskite, allowing extremely high stability under 85 °C/85% relative humidity for 700 h and a high power conversion efficiency of 20.9% with spiro‐OMeTAD as a hole‐transporting material.

Abstract

Operational stability of perovskite solar cells has been a challenge from the beginning of perovskite research. In general, humidity and heat are the most well‐known degradation sources for perovskites, requiring ideal design of perovskite chemistry to withstand them. Although triple‐cation perovskite (Cs_0.05(FA_0.85MA_0.15)_0.95Pb(I_0.85Br_0.15)₃) has been already introduced as the stable perovskite material, the high reactivity of methylammonium and formamidinium in the cation sites demands further modification. Herein, 1,2,4‐triazole is suggested as an effective cation solute to improve the performance and stability of perovskite solar cells. 1,2,4‐Triazole is an aromatic cation with low dipole moment that is stable under humidity and heat. It also possesses three nitrogen atoms, forming additional hydrogen bonds in the lattice, stabilizing the material. In this study, the solar cell utilizing 1,2,4‐triazole alloying achieves a power conversion efficiency of 20.9% with superior stability under extreme condition (85 °C/85% of relative humidity (RH), encapsulated) for 700 h. The 1,2,4‐triazole‐alloyed perovskite exhibits reduced trap density and film roughness and enhanced carrier lifetime with electrical conductivity, suggesting an ideal perovskite structure for efficient and stable optoelectronic applications.

A thin layer of C₆₀ pyrrolidine tris‐acid is found essential for achieving high efficiency with planar solar cells of Sn‐based perovskites. As a result, a power conversion efficiency of 7.40% is achieved for FASnI₃ solar cells with a planar n–i–p architecture. For the first time, highly efficient Sn‐based hybrid perovskite solar cells on n–i–p architecture is achieved.

Abstract

For solar cell applications, Sn‐based hybrid perovskites have drawn particular interest due to their environmental friendliness. Here, a thin layer of C₆₀ pyrrolidine tris‐acid (CPTA) is found essential for achieving high efficiency with planar solar cells of Sn‐based perovskites. As a result, a power conversion efficiency of 7.40% is achieved for {en}FASnI₃ solar cells with a planar n–i–p architecture, and the device exhibits excellent stability in air. For the first time, highly efficient Sn‐based hybrid perovskite solar cells on n–i–p architecture are achieved. A V _oc of 0.72 V is highlighted as the highest V _oc ever reported for FASnI₃ solar cells.

A new approach to ubiquitous sensing for indoor applications is presented, using low‐cost indoor perovskite photovoltaic cells as external power sources for backscatter sensors. Wide‐bandgap perovskite photovoltaic cells for indoor light energy harvesting are presented with the 1.63 and 1.84 eV devices that demonstrate efficiencies of 21% and 18.5%, respectively, under indoor compact fluorescent lighting.

Abstract

A new approach to ubiquitous sensing for indoor applications is presented, using low‐cost indoor perovskite photovoltaic cells as external power sources for backscatter sensors. Wide‐bandgap perovskite photovoltaic cells for indoor light energy harvesting are presented with the 1.63 and 1.84 eV devices that demonstrate efficiencies of 21% and 18.5%, respectively, under indoor compact fluorescent lighting, with a champion open‐circuit voltage of 0.95 V in a 1.84 eV cell under a light intensity of 0.16 mW cm⁻². Subsequently, a wireless temperature sensor self‐powered by a perovskite indoor light‐harvesting module is demonstrated. Three perovskite photovoltaic cells are connected in series to create a module that produces 14.5 µW output power under 0.16 mW cm⁻² of compact fluorescent illumination with an efficiency of 13.2%. This module is used as an external power source for a battery‐assisted radio‐frequency identification temperature sensor and demonstrates a read range by of 5.1 m while maintaining very high frequency measurements every 1.24 s. The combined indoor perovskite photovoltaic modules and backscatter radio‐frequency sensors are further discussed as a route to ubiquitous sensing in buildings given their potential to be manufactured in an integrated manner at very low cost, their lack of a need for battery replacement, and the high frequency data collection possible.