Mahui

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.

The essential advances in perovskite semiconductor‐based radiation detectors, mainly X‐ray and γ‐ray detectors, are reviewed. The promising properties of lead halide perovskites and recent advancements in material preparation, device design, and material improvement for radiation detector applications are discussed. A brief outlook for the further development of lead halide perovskite‐based radiation detectors is also provided.

Research interest in lead halide perovskites has shown a spurt of growth in the last few years due to their high absorption coefficient, large carrier mobility, and long diffusion length. Besides their wide applications in solar cells, LEDs, lasers, and photodetectors, lead halide perovskites are demonstrated as excellent candidate materials for radiation detectors with comparable performance to commercial Si and CdZnTe (CZT) detectors. Herein, the essential results on perovskite semiconductor‐based radiation conductors are summarized. Furthermore, a brief outlook for the further development of lead halide perovskites‐based radiation detectors is proposed.

Planar perovskite solar cells (PSCs) are promising photovoltaic devices accompanied with the obvious advantages of easy fabrication and scalability. Herein, a method toward obtaining high‐quality FA_1–x MA _x PbI₃ film‐based planar PSCs by sequential deposition of chlorobenzene and methylammonium chloride is proposed. A champion power conversion efficiency (PCE) of 18.57% is achieved and 91% of the initial PCE is maintained after 500 h.

Planar perovskite solar cells (PSCs) are promising photovoltaic devices accompanied with the obvious advantages of easy fabrication and scalability. To achieve highly efficient and stable PSCs, the morphology control of perovskite crystallization is crucial. Herein, a novel method toward obtaining high‐quality FA_1–x MA _x PbI₃ films by spin coating methylammonium chloride (MACl) and chlorobenzene (CB) in different sequential processes on the top of substrates is proposed. Controlling the nucleation process is beneficial for the formation of a homogeneous nucleus at the nucleation stage, leading to highly ordered seed crystals and an ultrasmooth perovskite film. As determined by photoluminescence and time‐resolved photoluminescence spectroscopy, the defects and the associated charge recombination are notably reduced by the high crystalline quality of perovskite film. Finally, a champion power conversion efficiency (PCE) of 18.57% is achieved and 91% of the initial PCE is retained after 500 h. The devices are stored in an ambient condition with 20% relative humidity (RH) at 30 °C in the dark.

Self‐assembled monolayers (SAMs) in perovskite solar cells are summarized comprehensively herein. SAMs play significant roles such as boosting the optoelectronic properties and improving perovskite stability. An overview of SAM modification in perovskite solar cells and state‐of‐the‐art applications is provided. Finally, the remaining challenges and outlooks for future research are presented.

Perovskite solar cells (PSCs) are considered as potential candidates for next‐generation energy harvesting due to their advantages. A classic PSC has two charge transport layers (CTLs) above and below a perovskite layer, and these CTLs largely influence charge extraction and transport. Thus, an interface inevitably forms between the CTL and perovskite layer, and if the CTL and perovskite do not form a compact contact, these interfaces can become a nonradiative recombination center, which can degrade device efficiency and stability. Accordingly, interface engineering is considered an effective way to alleviate this issue. Herein, an overview of interface engineering methods on PSCs is provided, particularly with regard to types of self‐assembled monolayers and their roles in device energy level alignment and passivation effects.

A facile method is reported for preparing α‐CsPbI₃ perovskite films at room temperature by introducing ascorbic acid (AA) in the CsPbI₃ precursor solution. The champion device not only showed a high efficiency of 11.44% but also had excellent stability, retaining more than 76% of its initial efficiency after aging in ambient conditions for 250 h without encapsulation.

The all‐inorganic α‐CsPbI₃ perovskite with superb thermal stability and suitable band gap for light harvesting has been considered as a promising candidate for efficient perovskite solar cells (PSCs). However, the photoactive black α‐CsPbI₃ is thermodynamically unstable and transforms spontaneously into nonphotoactive yellow δ‐phase at room temperature. Herein, a facile method is reported to prepare α‐CsPbI₃ perovskite films with high stability at room temperature by mixing a small amount of ascorbic acid (AA) in the CsPbI₃ precursor solutions. It is revealed that the interaction of AA with the CsPbI₃ precursors could effectively inhibit the rapid crystallization of CsPbI₃ and reduce the size of the coordination colloidal, and thus decrease the grain size of CsPbI₃ for preparing long‐term stable α‐CsPbI₃ films. The PSCs based on the AA‐stabilized CsPbI₃ films exhibit reproducible photovoltaic performance with a champion efficiency of up to 11.44% and stable output of 11.30%, along with excellent stability, retaining more than 76% of its initial efficiency after aging in ambient conditions for 250 h without encapsulation. Most importantly, such low‐cost, solution‐processable inorganic PSCs with high performance also show promising potential for large‐scale preparation.

A two‐step spin‐coating procedure is used to fabricate a chlorophyll derivative (CHL) and [6,6]‐phenyl‐C₇₁‐butyric acid methyl ester (PC₇₁BM)‐based “bilayer” (BL) organic solar cells in comparison with the bulk heterojunction (BHJ) devices. The BL devices yield a high efficiency, over 5%, which is much higher than that of the BHJ devices due to better CHL aggregate phase retention.

The power conversion efficiency (PCE) of chlorophyll (Chl)‐based organic solar cells (OSCs) is generally about 2%. Herein, a Chl‐a derivative (CHL) and [6,6]‐phenyl‐C₇₁‐butyric acid methyl ester (PC₇₁BM) are successfully used to fabricate Chl‐based OSCs with PCE over 5%. Two different preparation methods are used to prepare the active layer: 1) two‐step spin‐coating the self‐aggregated CHL and PC₇₁BM solutions sequentially and 2) one‐step spin‐coating the solution of CHL:PC₇₁BM blends, forming the “bilayer” (BL) and traditional bulk heterojunction (BHJ) configurations, respectively. Based on the aforementioned two kinds of active‐layer preparation methods, both inverted and regular types of OSCs are successfully investigated. All four types of devices work normally, which is likely due to the ambipolar characteristics of the CHL aggregate. Unexpectedly, the BL‐based devices yield PCEs of 5.17% for the regular type and 5.19% for the inverted type, which are higher than those of the BHJ‐based devices (3.96% for the regular type and 3.50% for the inverted type). The main improvement in PCEs of BL‐based devices comes from the enhanced short‐circuit currents, which is due to the decreased charge transfer resistance and enlarged photocurrent contribution of PC₇₁BM as well as slightly enhanced electron and hole mobilities.

A comprehensive and in‐depth understanding of fundamental polycrystalline perovskite film formation is first summarized, which provides a guidance base for various solution processing methods. Benefitting from the development of film manufacture, small‐ and large‐scale perovskite films with high quality are obtained, which contribute to the excellent performance in photovoltaics and stability of perovskite solar cells.

In recent years, tremendous research interest has been devoted to organic–inorganic halide perovskites because of their excellent optical and electrical properties, which make them intriguing photovoltaic materials. The recorded efficiency of Pb‐based halide perovskite solar cells (PSCs) has gone beyond 24%, thus fulfilling their potential for industrialization. The photovoltaic performance of PSCs is predominantly determined by the quality of the perovskite film, which in turn, is controlled by the fabrication process. Therefore, a comprehensive and in‐depth understanding of fundamental polycrystalline perovskite film formation is imperative for further development of PSC manufacturing. This review summarizes recent advances in the field of PSCs and mainly reviews the fundamental knowledge of nucleation and growth during perovskite crystallization from solution processing methods and promising small area and large‐scale solution manufacturing methods combined with their properties and relevant PSC performance. A brief overview of stabilization strategies and cost discussion is then presented. Finally, the challenges and outlooks of PSC development for upcoming photovoltaic technology for industrial application are discussed.

Two novel donor–acceptor‐type hole‐transporting materials are developed and characterized. Due to the good energy level alignment, appropriate hole‐transporting ability, and most importantly, the excellent film morphology, the MPA‐BTTI‐based dopant‐free inverted perovskite solar cell exhibits a remarkable power conversion efficiency of 21.17% with negligible hysteresis and long‐time operational stability.

Abstract

Hole‐transporting materials (HTMs) play a critical role in realizing efficient and stable perovskite solar cells (PVSCs). Considering their capability of enabling PVSCs with good device reproducibility and long‐term stability, high‐performance dopant‐free small‐molecule HTMs (SM‐HTMs) are greatly desired. However, such dopant‐free SM‐HTMs are highly elusive, limiting the current record efficiencies of inverted PVSCs to around 19%. Here, two novel donor–acceptor‐type SM‐HTMs (MPA‐BTI and MPA‐BTTI) are devised, which synergistically integrate several design principles for high‐performance HTMs, and exhibit comparable optoelectronic properties but distinct molecular configuration and film properties. Consequently, the dopant‐free MPA‐BTTI‐based inverted PVSCs achieve a remarkable efficiency of 21.17% with negligible hysteresis and superior thermal stability and long‐term stability under illumination, which breaks the long‐time standing bottleneck in the development of dopant‐free SM‐HTMs for highly efficient inverted PVSCs. Such a breakthrough is attributed to the well‐aligned energy levels, appropriate hole mobility, and most importantly, the excellent film morphology of the MPA‐BTTI. The results underscore the effectiveness of the design tactics, providing a new avenue for developing high‐performance dopant‐free SM‐HTMs in PVSCs.

Ternary polymer solar cells are successfully developed by combining a fullerene derivative and a nonfullerene material as acceptors. The introduction of PC₆₁BM into the PBDB‐TF:Y6 blend effectively improves the charge transport properties and reduces the nonradiative energy loss. Ultimately, the main photovoltaic parameters are simultaneously enhanced in the ternary devices, leading to an outstanding efficiency of 16.5% (certificated as 16.2%).

Abstract

Recent advances in the material design and synthesis of nonfullerene acceptors (NFAs) have revealed a new landscape for polymer solar cells (PSCs) and have boosted the power conversion efficiencies (PCEs) to over 15%. Further improvements of the photovoltaic performance are a significant challenge in NFA‐PSCs based on binary donor:acceptor blends. In this study, ternary PSCs are fabricated by incorporating a fullerene derivative, PC₆₁BM, into a combination of a polymer donor (PBDB‐TF) and a fused‐ring NFA (Y6) and a very high PCE of 16.5% (certified as 16.2%) is recorded. Detailed studies suggest that the loading of PC₆₁BM into the PBDB‐TF:Y6 blend can not only enhance the electron mobility but also can increase the electroluminescence quantum efficiency, leading to balanced charge transport and reduced nonradiative energy losses simultaneously. This work suggests that utilizing the complementary advantages of fullerene and NFAs is a promising way to finely tune the detailed photovoltaic parameters and further improve the PCEs of PSCs.

A platinum(II) complexation strategy is developed to regulate the crystallinity of a newly designed s‐tetrazine‐containing wide‐bandgap copolymer donor PSFTZ, and optimize the morphology of the PSFTZ:Y6 active blend film, which boosts successfully the power conversion efficiency of the resulting nonfullerene polymer solar cells (NF‐PSCs) from 13.03% to 16.35%. 16.35% is the new record for single‐junction NA‐PSCs at present.

Abstract

A new strategy of platinum(II) complexation is developed to regulate the crystallinity and molecular packing of polynitrogen heterocyclic polymers, optimize the morphology of the active blends, and improve the efficiency of the resulting nonfullerene polymer solar cells (NF‐PSCs). The newly designed s‐tetrazine (s‐TZ)‐containing copolymer of PSFTZ (4,8‐bis(5‐((2‐butyloctyl)thio)‐4‐fluorothiophen‐2‐yl)benzo[1,2‐b:4,5‐b′]dithiophene‐alt‐3,6‐bis(4‐octylthiophen‐2‐yl)‐1,2,4,5‐tetrazine) has a strong aggregation property, which results in serious phase separation and large domains when blending with Y6 ((2,2′‐((2Z,2′Z)‐((12,13‐bis(2‐ethylhexyl)‐3,9‐diundecyl‐12,13‐dihydro‐[1,2,5]thiadiazolo[3,4‐e]thieno[2″,3″:4′,5′]thieno[2′,3′:4,5]pyrrolo[3,2‐g]thieno[2′,3′:4,5]thieno[3,2‐b]indole‐2,10‐diyl)bis(methanylylidene))bis(5,6‐difluoro‐3‐oxo‐2,3‐dihydro‐1H‐indene‐2,1‐diylidene))dimalononitrile)), and produces a power‐conversion efficiency (PCE) of 13.03%. By adding small amount of Pt(Ph)₂(DMSO)₂ (Ph, phenyl and DMSO, dimethyl sulfoxide), platinum(II) complexation would occur between Pt(Ph)₂(DMSO)₂ and PSFTZ. The bulky benzene ring on the platinum(II) complex increases the steric hindrance along the polymer main chain, inhibits the polymer aggregation strength, regulates the phase separation, optimizes the morphology, and thus improves the efficiency to 16.35% in the resulting devices. 16.35% is the highest efficiency for single‐junction PSCs reported so far.

Large excitonic optical nonlinearity in single‐crystalline 2D Ruddlesden–Popper perovskite (RPP) nanosheets characterized by a microscopic Z‐scan setup is reported. A room‐temperature excitonic Mott transition occurs near the exciton resonance of the thinnest quantum‐well RPPs, boosting the nonlinear response. The magnitude and sign of the nonlinear coefficients vary strongly with the excitation wavelength offering various nonlinear functionalities in the visible waveband.

Abstract

Materials with large optical nonlinearity, especially in the visible spectral region, are in great demand for applications in all‐optical information processing and quantum optics. 2D hybrid Ruddlesden−Popper‐type halide perovskites (RPPs) with tunable ultraviolet‐to‐visible direct bandgaps exhibit large nonlinear optical responses due to the strong excitonic effects present in their multiple quantum wells. Using a microscopic Z‐scan setup with femtosecond laser pulses tunable across the visible spectrum, it is demonstrated that single‐crystalline lead halide RPP nanosheets possess unprecedentedly large nonlinear refraction and absorption coefficients near excitonic resonances. A room‐temperature insulator (exciton)–metal (plasma) Mott transition is found to occur near the exciton resonance of the thinnest qunatum‐well RPPs, boosting the nonlinear response. Owing to the rapidly changing refractive index near resonance, a single RPP crystal can exhibit different nonlinear functionalities across the excitation spectrum. The results suggest that RPPs are efficient nonlinear materials in the visible waveband, indicating their potential use in integrated nonlinear photonic applications such as optical modulation and switching.

By performing H/F substitution on the pyrrolidinium cation, homochirality is introduced to the cation while maintaining the 1D perovskite framework, following which two enantiomeric ferroelectrics are obtained: (R)‐ and (S)‐3‐F‐(pyrrolidinium)CdCl₃. The T _c is successfully increased from 240 K in the parent (pyrrolidinium)CdCl₃ to 303 K in these two enantiomers, making the ferroelectricity applicable at room temperature.

Abstract

A ferroelectric with a high phase‐transition temperature (T _c) is an indispensable condition for practical applications. Over the past decades, both strain engineering and the isotope effect have been found to effectively improve the T _c within ferroelectric material systems. However, the former strategy seems to prefer working in inorganic ferroelectric thin films, while the latter is also limited to some certain systems, such as hydrogen‐bonded ferroelectrics. It is noted that a mono‐fluorinated molecule is geometrically very similar to its parent molecule and the substitution of H by an F atom can introduce a chiral center on the molecule to template or stabilize polar structures. Significantly, the barrier of rotation of the fluorinated organic molecules is raised, resulting in a remarkable increase in T _c. Herein, by applying the molecular design strategy of H/F substitution to the organic–inorganic perovskite ferroelectric (pyrrolidinium)CdCl₃ with a low T _c of 240 K, two high‐T _c chiral perovskite ferroelectrics, (R)‐ and (S)‐3‐F‐(pyrrolidinium)CdCl₃ are successfully synthesized, for which the T _c reaches 303 K. The significant enhancement of 63 K in T _c extends the ferroelectric working temperature range to room temperature. This finding provides a new effective way to regulate the T _c in ferroelectrics and to design high‐T _c molecular ferroelectrics.

The factors affecting the V _OC in 2D perovskite cells with different [PbI₆]⁴⁻ layer sheets (n = 2–4) are elucidated. Nonradiative recombination at the perovskite/C₆₀ interface is found to dominate except for the n = 2 system where the bulk recombination determines the properties of the cell. Substantial V _OC gains through suppression of interfacial recombination at the top interface are expected.

Abstract

2D Ruddlesden–Popper perovskite (RPP) solar cells have excellent environmental stability. However, the power conversion efficiency (PCE) of RPP cells remains inferior to 3D perovskite‐based cells. Herein, 2D (CH₃(CH₂)₃NH₃)₂(CH₃NH₃) _{n −1}Pb _n I_{3 n +1} perovskite cells with different numbers of [PbI₆]⁴⁻ sheets (n = 2–4) are analyzed. Photoluminescence quantum yield (PLQY) measurements show that nonradiative open‐circuit voltage (V _OC) losses outweigh radiative losses in materials with n > 2. The n = 3 and n = 4 films exhibit a higher PLQY than the standard 3D methylammonium lead iodide perovskite although this is accompanied by increased interfacial recombination at the top perovskite/C₆₀ interface. This tradeoff results in a similar PLQY in all devices, including the n = 2 system where the perovskite bulk dominates the recombination properties of the cell. In most cases the quasi‐Fermi level splitting matches the device V _OC within 20 meV, which indicates minimal recombination losses at the metal contacts. The results show that poor charge transport rather than exciton dissociation is the primary reason for the reduction in fill factor of the RPP devices. Optimized n = 4 RPP solar cells had PCEs of 13% with significant potential for further improvements.

Perovskite solar cells based on polarized ferroelectric polymers are fabricated by doping the ferroelectric polymer into the perovskite layer with different polarizing electric fields and different doping concentrations, different polarized ferroelectric polymers' interlayers between the perovskite and the hole‐transporting layer, and both doping and interlayer. After these treatments, the fabricated devices show a maximum power conversion efficiency of 21.38%.

Abstract

In hybrid organic–inorganic lead halide perovskite solar cells, the energy loss is strongly associated with nonradiative recombination in the perovskite layer and at the cell interfaces. Here, a simple but effective strategy is developed to improve the cell performance of perovskite solar cells via the combination of internal doping by a ferroelectric polymer and external control by an electric field. A group of polarized ferroelectric (PFE) polymers are doped into the methylammonium lead iodide (MAPbI₃) layer and/or inserted between the perovskite and the hole‐transporting layers to enhance the build‐in field (BIF), improve the crystallization of MAPbI₃, and regulate the nonradiative recombination in perovskite solar cells. The PFE polymer‐doped MAPbI₃ shows an orderly arrangement of MA⁺ cations, resulting in a preferred growth orientation of polycrystalline perovskite films with reduced trap states. In addition, the BIF is enhanced by the widened depletion region in the device. As an interfacial dipole layer, the PFE polymer plays a critical role in increasing the BIF. This combined effect leads to a substantial reduction in voltage loss of 0.14 V due to the efficient suppression of nonradiative recombination. Consequently, the resulting perovskite solar cells present a power conversion efficiency of 21.38% with a high open‐circuit voltage of 1.14 V.

Two novel donor–acceptor‐type hole‐transporting materials are developed and characterized. Due to the good energy level alignment, appropriate hole‐transporting ability, and most importantly, the excellent film morphology, the MPA‐BTTI‐based dopant‐free inverted perovskite solar cell exhibits a remarkable power conversion efficiency of 21.17% with negligible hysteresis and long‐time operational stability.

Abstract

Hole‐transporting materials (HTMs) play a critical role in realizing efficient and stable perovskite solar cells (PVSCs). Considering their capability of enabling PVSCs with good device reproducibility and long‐term stability, high‐performance dopant‐free small‐molecule HTMs (SM‐HTMs) are greatly desired. However, such dopant‐free SM‐HTMs are highly elusive, limiting the current record efficiencies of inverted PVSCs to around 19%. Here, two novel donor–acceptor‐type SM‐HTMs (MPA‐BTI and MPA‐BTTI) are devised, which synergistically integrate several design principles for high‐performance HTMs, and exhibit comparable optoelectronic properties but distinct molecular configuration and film properties. Consequently, the dopant‐free MPA‐BTTI‐based inverted PVSCs achieve a remarkable efficiency of 21.17% with negligible hysteresis and superior thermal stability and long‐term stability under illumination, which breaks the long‐time standing bottleneck in the development of dopant‐free SM‐HTMs for highly efficient inverted PVSCs. Such a breakthrough is attributed to the well‐aligned energy levels, appropriate hole mobility, and most importantly, the excellent film morphology of the MPA‐BTTI. The results underscore the effectiveness of the design tactics, providing a new avenue for developing high‐performance dopant‐free SM‐HTMs in PVSCs.

Ternary polymer solar cells are successfully developed by combining a fullerene derivative and a nonfullerene material as acceptors. The introduction of PC₆₁BM into the PBDB‐TF:Y6 blend effectively improves the charge transport properties and reduces the nonradiative energy loss. Ultimately, the main photovoltaic parameters are simultaneously enhanced in the ternary devices, leading to an outstanding efficiency of 16.5% (certificated as 16.2%).

Abstract

Recent advances in the material design and synthesis of nonfullerene acceptors (NFAs) have revealed a new landscape for polymer solar cells (PSCs) and have boosted the power conversion efficiencies (PCEs) to over 15%. Further improvements of the photovoltaic performance are a significant challenge in NFA‐PSCs based on binary donor:acceptor blends. In this study, ternary PSCs are fabricated by incorporating a fullerene derivative, PC₆₁BM, into a combination of a polymer donor (PBDB‐TF) and a fused‐ring NFA (Y6) and a very high PCE of 16.5% (certified as 16.2%) is recorded. Detailed studies suggest that the loading of PC₆₁BM into the PBDB‐TF:Y6 blend can not only enhance the electron mobility but also can increase the electroluminescence quantum efficiency, leading to balanced charge transport and reduced nonradiative energy losses simultaneously. This work suggests that utilizing the complementary advantages of fullerene and NFAs is a promising way to finely tune the detailed photovoltaic parameters and further improve the PCEs of PSCs.

A poly(3,4‐ethylenedioxythiophene)‐free and indium tin oxide (ITO)‐free junction‐free AgNN electrode with high optoelectrical properties is proposed for flexible organic solar cells (FOSCs). The electrical sheet resistance and optical transmittance can be controlled by both initial metal thickness and NN density; even a very thin Ag layer with appropriate NN density can show high transmittance and low sheet resistance, yielding a highly efficient FOSC.

Abstract

A novel approach to fabricate flexible organic solar cells is proposed without indium tin oxide (ITO) and poly(3,4‐ethylenedioxythiophene):poly(styrenesulfonate) (PEDOT:PSS) using junction‐free metal nanonetworks (NNs) as transparent electrodes. The metal NNs are monolithically etched using nanoscale shadow masks, and they exhibit excellent optoelectronic performance. Furthermore, the optoelectrical properties of the NNs can be controlled by both the initial metal layer thickness and NN density. Hence, with an extremely thin silver layer, the appropriate density control of the networks can lead to high transmittance and low sheet resistance. Such NNs can be utilized for thin‐film devices without planarization by conductive materials such as PEDOT:PSS. A highly efficient flexible organic solar cell with a power conversion efficiency (PCE) of 10.6% and high device yield (93.8%) is fabricated on PEDOT‐free and ITO‐free transparent electrodes. Furthermore, the flexible solar cell retains 94.3% of the initial PCE even after 3000 bending stress tests (strain: 3.13%).

The progress of research into metal cations for perovskite solar cells is discussed by focusing on the locations of the cations in perovskites, the modulation of the film quality, and the influence on the photovoltaic performance. Metal cations are considered in the order of alkali cations, alkaline earth cations, and then metal cations in the ds and d regions, and ultimately trivalent cations.

Abstract

Metal halide perovskite solar cells (PVSCs) have revolutionized photovoltaics since the first prototype in 2009, and up to now the highest efficiency has soared to 24.2%, which is on par with commercial thin film cells and not far from monocrystalline silicon solar cells. Optimizing device performance and improving stability have always been the research highlight of PVSCs. Metal cations are introduced into perovskites to further optimize the quality, and this strategy is showing a vigorous development trend. Here, the progress of research into metal cations for PVSCs is discussed by focusing on the position of the cations in perovskites, the modulation of the film quality, and the influence on the photovoltaic performance. Metal cations are considered in the order of alkali cations, alkaline earth cations, then metal cations in the ds and d regions, and ultimately trivalent cations (p‐ and f‐block metal cations) according to the periodic table of elements. Finally, this work is summarized and some relevant issues are discussed.

In article number https://doi.org/10.1002/adma.2019016441901644, Babar Shabbir, Yupeng Zhang, Qiaoliang Bao, and co‐workers utilize inexpensive inkjet printing to homogeneously print a perovskite film consisting of all‐inorganic halide perovskite quantum dots on various substrates, which they further develop into an X‐ray detector. This type of detector is an ideal candidate for applications in soft/hard X‐ray detection and large‐area flat/flexible imaging technologies.

Perovskite solar cells based on polarized ferroelectric polymers are fabricated by doping the ferroelectric polymer into the perovskite layer with different polarizing electric fields and different doping concentrations, different polarized ferroelectric polymers' interlayers between the perovskite and the hole‐transporting layer, and both doping and interlayer. After these treatments, the fabricated devices show a maximum power conversion efficiency of 21.38%.

Abstract

In hybrid organic–inorganic lead halide perovskite solar cells, the energy loss is strongly associated with nonradiative recombination in the perovskite layer and at the cell interfaces. Here, a simple but effective strategy is developed to improve the cell performance of perovskite solar cells via the combination of internal doping by a ferroelectric polymer and external control by an electric field. A group of polarized ferroelectric (PFE) polymers are doped into the methylammonium lead iodide (MAPbI₃) layer and/or inserted between the perovskite and the hole‐transporting layers to enhance the build‐in field (BIF), improve the crystallization of MAPbI₃, and regulate the nonradiative recombination in perovskite solar cells. The PFE polymer‐doped MAPbI₃ shows an orderly arrangement of MA⁺ cations, resulting in a preferred growth orientation of polycrystalline perovskite films with reduced trap states. In addition, the BIF is enhanced by the widened depletion region in the device. As an interfacial dipole layer, the PFE polymer plays a critical role in increasing the BIF. This combined effect leads to a substantial reduction in voltage loss of 0.14 V due to the efficient suppression of nonradiative recombination. Consequently, the resulting perovskite solar cells present a power conversion efficiency of 21.38% with a high open‐circuit voltage of 1.14 V.

A semitransparent photovoltaic (ST‐PV) with a tandem architecture and selective absorption in invisible regions is designed. By developing highly efficient active layers that selective absorb in the UV and near‐infrared regions and designing an appropriate interconnecting layer and transparent electrode, the resulting tandem ST‐PV device exhibits light utilization efficiency of 5.7% with averaged visible transmittance (AVT) of 52.9% and power conversion efficiency up to 10.7%.

Abstract

Semitransparent (ST) photovoltaics (PVs) with selective absorption in the UV or/and near‐infrared (NIR) range(s) and reduced energy losses, are critical for high‐efficiency solar‐window applications. Here, a high‐performance tandem ST‐PV with selected absorption in the desirable regions of the solar spectrum is demonstrated. An ultralarge‐bandgap perovskite film (FAPbBr_2.43Cl_0.57, E _g ≈ 2.36 eV) is first developed to fulfil efficient selective absorption in the UV region. After optimization, the corresponding ST single junction (SJ) PV exhibits an averaged transmittance (AVT) of ≈68% and an efficiency of ≈7.5%. By sequentially reducing the visible absorbing component in a low‐bandgap organic bulk‐heterojunction layer, an ST‐PV with selective absorption in the NIR is achieved with a power conversion efficiency (PCE) of 5.9% and a high AVT of 62%. The energy loss associated with the SJ ST‐PVs is further reduced with a tandem architecture, which affords a high PCE of 10.7%, an AVT of 52.91%, and a light utilization efficiency up to 5.66%. These results represent the best balance of AVT and PCE among all ST‐PVs reported so far, and this design should pave the road for solar windows of high performance.

The power conversion efficiency of perovskite colloidal quantum dot (CQD) solar cells is improved using a conjugated small molecule, ITIC. The carrier dynamics of this unique perovskite CQD/ITIC system are investigated, showing an effective carrier transfer from the perovskite CQDs to the ITIC, which provides an additional driving force for charge separation in perovskite CQDs photovoltaic devices and boosts the efficiency up to 12.7%.

Abstract

Halide perovskite colloidal quantum dots (CQDs) have recently emerged as a promising candidate for CQD photovoltaics due to their superior optoelectronic properties to conventional chalcogenides CQDs. However, the low charge separation efficiency due to quantum confinement still remains a critical obstacle toward higher‐performance perovskite CQD photovoltaics. Available strategies employed in the conventional CQD devices to enhance the carrier separation, such as the design of type‐Ⅱ core–shell structure and versatile surface modification to tune the electronic properties, are still not applicable to the perovskite CQD system owing to the difficulty in modulating surface ligands and structural integrity. Herein, a facile strategy that takes advantage of conjugated small molecules that provide an additional driving force for effective charge separation in perovskite CQD solar cells is developed. The resulting perovskite CQD solar cell shows a power conversion efficiency approaching 13% with an open‐circuit voltage of 1.10 V, short‐circuit current density of 15.4 mA cm⁻², and fill factor of 74.8%, demonstrating the strong potential of this strategy toward achieving high‐performance perovskite CQD solar cells.

A semitransparent photovoltaic (ST‐PV) with a tandem architecture and selective absorption in invisible regions is designed. By developing highly efficient active layers that selective absorb in the UV and near‐infrared regions and designing an appropriate interconnecting layer and transparent electrode, the resulting tandem ST‐PV device exhibits light utilization efficiency of 5.7% with averaged visible transmittance (AVT) of 52.9% and power conversion efficiency up to 10.7%.

Abstract

Semitransparent (ST) photovoltaics (PVs) with selective absorption in the UV or/and near‐infrared (NIR) range(s) and reduced energy losses, are critical for high‐efficiency solar‐window applications. Here, a high‐performance tandem ST‐PV with selected absorption in the desirable regions of the solar spectrum is demonstrated. An ultralarge‐bandgap perovskite film (FAPbBr_2.43Cl_0.57, E _g ≈ 2.36 eV) is first developed to fulfil efficient selective absorption in the UV region. After optimization, the corresponding ST single junction (SJ) PV exhibits an averaged transmittance (AVT) of ≈68% and an efficiency of ≈7.5%. By sequentially reducing the visible absorbing component in a low‐bandgap organic bulk‐heterojunction layer, an ST‐PV with selective absorption in the NIR is achieved with a power conversion efficiency (PCE) of 5.9% and a high AVT of 62%. The energy loss associated with the SJ ST‐PVs is further reduced with a tandem architecture, which affords a high PCE of 10.7%, an AVT of 52.91%, and a light utilization efficiency up to 5.66%. These results represent the best balance of AVT and PCE among all ST‐PVs reported so far, and this design should pave the road for solar windows of high performance.

The power conversion efficiency of perovskite colloidal quantum dot (CQD) solar cells is improved using a conjugated small molecule, ITIC. The carrier dynamics of this unique perovskite CQD/ITIC system are investigated, showing an effective carrier transfer from the perovskite CQDs to the ITIC, which provides an additional driving force for charge separation in perovskite CQDs photovoltaic devices and boosts the efficiency up to 12.7%.

Abstract

Halide perovskite colloidal quantum dots (CQDs) have recently emerged as a promising candidate for CQD photovoltaics due to their superior optoelectronic properties to conventional chalcogenides CQDs. However, the low charge separation efficiency due to quantum confinement still remains a critical obstacle toward higher‐performance perovskite CQD photovoltaics. Available strategies employed in the conventional CQD devices to enhance the carrier separation, such as the design of type‐Ⅱ core–shell structure and versatile surface modification to tune the electronic properties, are still not applicable to the perovskite CQD system owing to the difficulty in modulating surface ligands and structural integrity. Herein, a facile strategy that takes advantage of conjugated small molecules that provide an additional driving force for effective charge separation in perovskite CQD solar cells is developed. The resulting perovskite CQD solar cell shows a power conversion efficiency approaching 13% with an open‐circuit voltage of 1.10 V, short‐circuit current density of 15.4 mA cm⁻², and fill factor of 74.8%, demonstrating the strong potential of this strategy toward achieving high‐performance perovskite CQD solar cells.