Ligang Yuan

Large energy loss has been a major obstacle for further efficiency improvement of inorganic perovskite solar cells. This review provides a basic understanding of energy loss and may inspire new designs or more impactful methods for further minimizing the energy loss of inorganic perovskite solar cells.

Abstract

Though the cesium‐based inorganic perovskite solar cells (IPSCs) have developed rapidly in recent two years, the power conversion efficiency (PCE) is still far away from the Shockley–Queisser limit due to the large open‐circuit voltage (V _oc) deficit, which results from the large energy loss (E _loss). Large E _loss has been a major obstacle for further efficiency improvement of IPSCs. In this review, the authors, for the first time, focus on investigating the E _loss of IPSCs and start from discussing the essence and origin of the E _loss. Then, the reported efficient methods for reducing the band tails and energy disorder are systematically summarized and reviewed, including crystallization optimization, defect passivation, and interface engineering. Finally, the authors offer an overall perspective on managing E _loss in IPSCs and point out the possible ways to reduce the E _loss and promote the efficiency. This review provides a basic understanding of E _loss and may inspire new designs or more impactful methods for further minimizing the E _loss of IPSCs.

CuGaO₂ nanoparticles modified with aminosilane are used as a hole‐transporting layer with CuSCN for perovskite solar cells. The enhanced power conversion efficiency and thermal stability compared to the cell using only CuSCN are correlated with the improved carrier extraction and reduced interfacial degradation by the inorganic nanoparticles.

Abstract

Herein, solution‐processible inorganic hole‐transport layer (HTL) of a perovskite solar cell that consists of CuGaO₂ nanoparticles and CuSCN, which leads to an improved device performance as well as long‐term stability, is reported. Uniform films of CuGaO₂ are prepared by first treating CuGaO₂ nanoparticles with aminosilane that leads to well‐dispersed CuGaO₂ solution, followed by spin‐coating of the suspension. Subsequent spin‐coating of CuSCN solution onto the CuGaO₂ forms a smooth HTL with excellent coverage and electrical conductivity. Comparing to the reference device with CuSCN HTL, the CuGaO₂/CuSCN device improves carrier extraction and reduces trap density by ≈40%, as measured by photoluminescence and capacitance analysis. Excellent thermal stability is also demonstrated: ≈80% of the initial efficiency of the perovskite solar cells with the CuGaO₂/CuSCN HTL is retained after 400 h under 85 °C/85% relative humidity environment.

Upscaling loss for perovskite devices is higher than for any other photovoltaic technology. Herein, electroluminescence, dark lock‐in thermography, microphotoluminescence spectroscopy, and electron spectroscopy are used to investigate upscaling losses, focusing on layer inhomogeneities for modules with an aperture area up to 100 cm². Analysis helps in identification of processing pitfalls and strategies for overcoming or minimizing their effects.

Hybrid metal‐halide perovskite‐based thin‐film photovoltaics (PVs) have the potential to become the next generation of commercialized PV technology with certified power conversion efficiencies reaching 24% on devices having 0.1 cm² area. Recent efforts in upscaling this technology result in an efficiency of 12.6% for 354 cm² modules. However, upscaling loss for perovskite‐based PVs is higher than for any other PV technology. In this study, upscaling losses of devices with aperture area 0.1, 4, and 100 cm² are investigated, with a focus on layer inhomogeneities. Electroluminescence, dark lock‐in thermography, microphotoluminescence spectroscopy, and electron spectroscopy are used to analyze and group layer inhomogeneities with a minimal size of 10 μm and to compare loss mechanisms for radial and linear deposition techniques. Analysis results help to identify current processing pitfalls, where understanding and control of perovskite crystal formation plays the crucial role.

An all‐layer‐inorganic perovskite solar cell (PSC) based on inorganic CsPbI₂Br perovskite absorber layer and tailored NiO hole‐transporting layer (HTL) is fabricated. The tailored NiO nanocrystalline films exhibit uniform, pinhole‐free morphologies, efficient charge‐extraction capabilities, and intrinsic chemical stability, which gives the whole photovoltaic device a high efficiency and much improved stability compared with PSCs based on the organic HTLs.

Cesium‐based inorganic perovskite solar cells (PSCs) have attracted great attention due to the superior thermal stability of the light absorbers. However, the reported devices normally contain organic charge‐transporting layers (CTLs), such as spiro‐OMeTAD, which is expensive and highly sensitive to ambient atmosphere and temperature. It is of great significance to develop inorganic CTLs with low cost and robust stability. To date, it is still a big challenge to achieve high‐quality inorganic CTL films via the solution process, especially for the hole‐transporting layer (HTL) in conventional n‐i‐p structures. Herein, tailored NiO nanocrystalline films as HTLs in an all‐layer‐inorganic CsPbI₂Br‐based PSCs are developed, which exhibit uniform, pinhole‐free morphologies and efficient charge‐extraction capabilities. Consequently, the as‐constructed all‐layer‐inorganic PSCs, with an optimal power conversion efficiency (PCE) of 15.14% and a stabilized power output of 14.82%, present robust long‐term thermal stability: retained 85% of their initial PCEs after a thermal treatment at 85 °C in the dark in a nitrogen atmosphere with encapsulation for 1000 h, greatly surpassing the performance of the PSCs based on the organic HTLs.

A UV‐inert ZnTiO₃ is demonstrated to be an electron selective layer in perovskite solar cells. ZnTiO₃ is a perovskite‐structured semiconductor with excellent chemical stability and poor photocatalysis. Planar perovskite solar cells based on ZnTiO₃ exhibit power conversion efficiency of 20.1% with improved photostability. The best device holds 90% of its initial efficiency after 100 h of ultraviolet soaking.

Abstract

Although planar‐structured perovskite solar cells (PSCs) have power conversion efficiencies exceeding 24%, the poor photostability, especially with ultraviolet irradiance (UV) severely limits commercial application. The most commonly‐used TiO₂ electron selective layer has a strong photocatalytic effect on perovskite/TiO₂ interface when TiO₂ is excited by UV light. Here a UV‐inert ZnTiO₃ is reported as the electron selective layer in planar PSCs. ZnTiO₃ is a perovskite‐structured semiconductor with excellent chemical stability and poor photocatalysis. Solar cells are fabricated with a structure of indium doped tin oxide (ITO)/ZnTiO₃/Cs_0.05FA_0.81MA_0.14PbI_2.55Br_0.45/Sprio‐MeOTAD/Au. The champion device exhibits a stabilized power conversion efficiency of 19.8% with improved photostability. The device holds 90% of its initial efficiency after 100 h of UV soaking (365 nm, 8 mW cm⁻²), compared with 55% for TiO₂‐based devices. This work provides a new class of electron selective materials with excellent UV stability in perovskite solar cell applications.

The role of DMAI in fabricating high quality CsPbI₃ inorganic perovskite thin films is demonstrated to be a volatile crystal growth additive rather than dopant. With optimal DMAI additive and PTACl passivation, a PTACl‐CsPbI₃ based champion photovoltaic device exhibits a record efficiency of 19.03 %.

Abstract

The controllable growth of CsPbI₃ perovskite thin films with desired crystal phase and morphology is crucial for the development of high efficiency inorganic perovskite solar cells (PSCs). The role of dimethylammonium iodide (DMAI) used in CsPbI₃ perovskite fabrication was carefully investigated. We demonstrated that the DMAI is an effective volatile additive to manipulate the crystallization process of CsPbI₃ inorganic perovskite films with different crystal phases and morphologies. The thermogravimetric analysis results indicated that the sublimation of DMAI is sensitive to moisture, and a proper atmosphere is helpful for the DMAI removal. The time‐of‐flight secondary ion mass spectrometry and nuclear magnetic resonance results confirmed that the DMAI additive would not alloy into the crystal lattice of CsPbI₃ perovskite. Moreover, the DMAI residues in CsPbI₃ perovskite can deteriorate the photovoltaic performance and stability. Finally, the PSCs based on phenyltrimethylammonium chloride passivated CsPbI₃ inorganic perovskite achieved a record champion efficiency up to 19.03 %.

A fully automated spray‐coated technology for the commercial large‐scale solution‐based processing of colloidal CsPbI₃ quantum dot films is achieved. The solar cells based on such films show a high power conversion efficiency of 11.2%.

Abstract

A fully automated spray‐coated technology with ultrathin‐film purification is exploited for the commercial large‐scale solution‐based processing of colloidal inorganic perovskite CsPbI₃ quantum dot (QD) films toward solar cells. This process is in the air outside the glove box. To further improve the performance of QD solar cells, the short‐chain ligand of phenyltrimethylammonium bromide (PTABr) with a benzene group is introduced to partially substitute for the original long‐chain ligands of the colloidal QD surface (namely PTABr‐CsPbI₃). This process not only enhances the carrier charge mobility within the QD film due to shortening length between adjacent QDs, but also passivates the halide vacancy defects of QD by Br⁻ from PTABr. The colloidal QD solar cells show a power conversion efficiency (PCE) of 11.2% with an open voltage of 1.11 V, a short current density of 14.4 mA cm⁻², and a fill factor of 0.70. Due to the hydrophobic surface chemistry of the PTABr–CsPbI₃ film, the solar cell can maintain 80% of the initial PCE in ambient conditions for one month without any encapsulation. Such a low‐cost and efficient spray‐coating technology also offers an avenue to the film fabrication of colloidal nanocrystals for electronic devices.

A 2D metal–organic framework In‐Aipa‐derived N‐rich porous carbon material with rich pyridinic‐N and graphitic‐N is first introduced into the hole transport layers of perovskite solar cells as an auxiliary additive, contributing to the significantly improved power conversion efficiency from 16.47% to 18.51%, as well as the enhanced long‐term stability of over 85% efficiency retention under exposure to air for 720 h.

As the standard bidopants of hole transport layers (HTLs) in perovskite solar cells (PSCs), bis(trifluoromethane)sulfonimide lithium salt (Li‐TFSI) and 4‐tert‐butylpyridine not only induce adverse influence on the quality of thin films, but also seriously impair the long‐term stability of devices. Herein, a metal–organic framework‐derived 2D graphitic N‐rich porous carbon (NPC) is first introduced into the HTLs as an effective auxiliary additive. The introduction of NPC significantly reduces the aggregation of lithium salts and the formation of HTL defects, optimizing film quality for rapid hole extraction and migration. Furthermore, inherent porosity and hydrophobicity of NPCs are extremely beneficial to restrict the permeation of Li⁺ ions and anode metals, and prevent the moisture from eroding the HTLs and perovskite layers, enhancing the stability of PSCs. As expected, the PSCs with NPC realize a satisfactory fill factor of 0.76 and power conversion efficiency (PCE) of 18.51%, apparently higher than that of pristine devices (0.70% and 16.47%). In addition, over 85% of the initial PCE for optimized PSCs is maintained after 720 h of exposure to air. Obviously, an innovative strategy for highly efficient and long‐term stable PSC devices is provided.

Recent progress in bandgap engineering strategies including the two main, widely used impurity and pressure as well as intermediate band, external electric field, and steric methods are reviewed comprehensively. Their underlying mechanism, achievements, and challenges are outlined. Additionally, future research directions are provided to realize direct and gap size continually tunable perovskites for further enhancing solar cell performance.

Metal halide perovskites are attractive for highly efficient solar cells. As most perovskites suffer large or indirect bandgap compared with the ideal bandgap range for single‐junction solar cells, bandgap engineering has received tremendous attention in terms of tailoring perovskite band structure, which plays a key role in light harvesting and conversion. In this Review, various reported bandgap engineering strategies are summarized. The recently widely used two main strategies including impurity and pressure as well as their underlying mechanisms are reviewed comprehensively. In addition, intermediate band and external electric field for bandgap engineering are also investigated. Moreover, future research directions are outlined to guide the further investigation.

Upscaling loss for perovskite devices is higher than for any other photovoltaic technology. Herein, electroluminescence, dark lock‐in thermography, microphotoluminescence spectroscopy, and electron spectroscopy are used to investigate upscaling losses, focusing on layer inhomogeneities for modules with an aperture area up to 100 cm². Analysis helps in identification of processing pitfalls and strategies for overcoming or minimizing their effects.

Hybrid metal‐halide perovskite‐based thin‐film photovoltaics (PVs) have the potential to become the next generation of commercialized PV technology with certified power conversion efficiencies reaching 24% on devices having 0.1 cm² area. Recent efforts in upscaling this technology result in an efficiency of 12.6% for 354 cm² modules. However, upscaling loss for perovskite‐based PVs is higher than for any other PV technology. In this study, upscaling losses of devices with aperture area 0.1, 4, and 100 cm² are investigated, with a focus on layer inhomogeneities. Electroluminescence, dark lock‐in thermography, microphotoluminescence spectroscopy, and electron spectroscopy are used to analyze and group layer inhomogeneities with a minimal size of 10 μm and to compare loss mechanisms for radial and linear deposition techniques. Analysis results help to identify current processing pitfalls, where understanding and control of perovskite crystal formation plays the crucial role.

UV‐ozone treatments for different times (0, 10, 30, and 60 min) are examined on the 2D metallic Ti₃C₂T_x films to take advantage of the tunable optoelectronic properties of MXenes as electron transport layers in low‐temperature processed planar‐structured perovskite solar cells, resulting in augmentation of the power conversion efficiency (PCE) from 5.00% to the champion PCE of 17.17%.

Abstract

MXenes are a large and rapidly expanding family of 2D materials that, owing to their unique optoelectronic properties and tunable surface termination, find a wide range of applications including energy storage and energy conversion. In this work, Ti₃C₂T_x MXene nanosheets are applied as a novel type of electron transport layer (ETL) in low‐temperature processed planar‐structured perovskite solar cells (PSCs). Interestingly, simple UV‐ozone treatment of the metallic Ti₃C₂T_x that increases the surface TiO bonds without any change in its bulk properties such as high electron mobility improves its suitability as an ETL. Improved electron transfer and suppressed recombination at the ETL/perovskite interface results in augmentation of the power conversion efficiency (PCE) from 5.00% in the case of Ti₃C₂T_x without UV‐ozone treatment to the champion PCE of 17.17%, achieved using the Ti₃C₂T_x film after 30 min of UV‐ozone treatment. As the first report on the use of pure MXene layer as an ETL in PSCs, this work shows the great potential of MXenes to be used in PSCs and displays their promise for applications in photovoltaic technology in general.

A 2D metal–organic framework In‐Aipa‐derived N‐rich porous carbon material with rich pyridinic‐N and graphitic‐N is first introduced into the hole transport layers of perovskite solar cells as an auxiliary additive, contributing to the significantly improved power conversion efficiency from 16.47% to 18.51%, as well as the enhanced long‐term stability of over 85% efficiency retention under exposure to air for 720 h.

As the standard bidopants of hole transport layers (HTLs) in perovskite solar cells (PSCs), bis(trifluoromethane)sulfonimide lithium salt (Li‐TFSI) and 4‐tert‐butylpyridine not only induce adverse influence on the quality of thin films, but also seriously impair the long‐term stability of devices. Herein, a metal–organic framework‐derived 2D graphitic N‐rich porous carbon (NPC) is first introduced into the HTLs as an effective auxiliary additive. The introduction of NPC significantly reduces the aggregation of lithium salts and the formation of HTL defects, optimizing film quality for rapid hole extraction and migration. Furthermore, inherent porosity and hydrophobicity of NPCs are extremely beneficial to restrict the permeation of Li⁺ ions and anode metals, and prevent the moisture from eroding the HTLs and perovskite layers, enhancing the stability of PSCs. As expected, the PSCs with NPC realize a satisfactory fill factor of 0.76 and power conversion efficiency (PCE) of 18.51%, apparently higher than that of pristine devices (0.70% and 16.47%). In addition, over 85% of the initial PCE for optimized PSCs is maintained after 720 h of exposure to air. Obviously, an innovative strategy for highly efficient and long‐term stable PSC devices is provided.

The fabrication method of high‐quality (Cs) _x (FA)_1−x PbI₃ perovskite films by varying the amount of cesium chloride (CsCl) in the FAPbI₃ precursor solutions is demonstrated. The best photovoltaic performance with a power conversion efficiency of 19.20% is achieved for the device with 10 mol% excess of CsCl.

The quality of perovskite films plays a crucial role in improving the optoelectronic properties and performance of perovskite solar cells (PSCs). Herein, high‐quality Cs _x FA_1−x PbI₃ perovskite films with different compositions (x = 0, 5, 10, and 15) are achieved by controlling the amount of cesium chloride (CsCl) in the respective FAPbI₃ precursor solution. The effects of CsCl addition on the morphological and optoelectronic properties of the resulting perovskite films and on the performance of the corresponding devices are systematically studied. Introduction of CsCl into FAPbI₃ shows a great potential to stabilize the α‐FAPbI₃ perovskite phase by forming Cs _x FA_1−x PbI₃ films with improved morphology and carrier lifetimes. With an optimal 10 mol% CsCl additive, the average power conversion efficiency (PCE) is increased from 16.83 ± 0.30% for the reference FAPbI₃‐based PSCs to 18.87 ± 0.25% (with a steady‐state PCE of 18.89%). Moreover, the optimized device performance is more stable after 20 days than the controlled one under ≈40% humidity in air.

CsF is adopted to modify the PbI₂ seed for highly crystallized Cs‐doped perovskite film with very long carrier lifetime, and very high light, thermal and humidity stabilities. As a result, the planar perovskite solar cells based on the Cs‐doped film also show very good stability with negligible hysteresis, and display PCEs of over 21%.

Abstract

Adding a small amount of CsI into mixed cation‐halide perovskite film via a one‐step method has been demonstrated as an excellent strategy for high‐performance perovskite solar cells (PSCs). However, the one‐step method generally relies on an antisolvent washing process, which is hard to control and not suitable for fabricating large‐area devices. Here, CsF is employed and Cs is incorporated into perovskite film via a two‐step method. It is revealed that CsF can effectively diffuse into the PbI₂ seed film, and drastically enhances perovskite crystallization, leading to high‐quality Cs‐doped perovskite film with a very long photoluminescence carrier lifetime (1413 ns), remarkable light stability, thermal stability, and humidity stability. The fabricated PSCs show power conversion efficiency (PCE) of over 21%, and they are highly thermally stable: in the aging test at 60 °C for 300 h, 96% of the original PCE remains. The CsF incorporation process provides a new avenue for stable high‐performance PSCs.

Herein, acetate anion (Ac⁻) is used to partially replace I⁻ in the CsPbI₂Br framework. Ac⁻ doping changes the morphology, electronic properties, and band structure of the host CsPbI₂Br film. The obtained CsPbI_{2− x} Br(Ac) _x perovskite solar cells exhibit a power conversion efficiency of 15.56%, an open circuit voltage of 1.30 V, and great air stability.

Abstract

The Cs‐based inorganic perovskite solar cells (PSCs), such as CsPbI₂Br, have made a striking breakthrough with power conversion efficiency (PCE) over 16% and potential to be used as top cells for tandem devices. Herein, I⁻ is partially replaced with the acetate anion (Ac⁻) in the CsPbI₂Br framework, producing multiple benefits. The Ac⁻ doping can change the morphology, electronic properties, and band structure of the host CsPbI₂Br film. The obtained CsPbI_{2− x} Br(Ac) _x perovskite films present lower trap densities, longer carrier lifetimes, and fast charge transportation compared to the host CsPbI₂Br films. Interestingly, the CsPbI_{2− x} Br(Ac) _x PSCs exhibit a maximum PCE of 15.56% and an ultrahigh open circuit voltage (V _oc) of 1.30 V without sacrificing photocurrent. Notably, such a remarkable V _oc is among the highest values of the previously reported CsPbI₂Br PSCs, while the PCE far exceeds all of them. In addition, the obtained CsPbI_{2− x} Br(Ac) _x PSCs exhibit high reproducibility and good stability. The stable CsPbI_{2− x} Br(Ac) _x PSCs with high V _oc and PCE are desirable for tandem solar cell applications.

Publication date: 18 December 2019

Source: Joule, Volume 3, Issue 12

Author(s): Sarthak Jariwala, Hongyu Sun, Gede W.P. Adhyaksa, Andries Lof, Loreta A. Muscarella, Bruno Ehrler, Erik C. Garnett, David S. Ginger

Context & Scale

Summary

Graphical Abstract

Two organic small molecules are presented as dopant‐free hole transporting materials (HTMs) in inverted perovskite solar cells, namely, FB‐OMeTPA and FT‐OMeTPA. Due to the Pb–S interaction at interfaces between HTM and perovskites, devices based on FT‐OMeTPA deliver an impressive power conversion efficiency of 17.57%, which is considerably higher than that of devices with FB‐OMeTPA (14.35%).

One of the attractive ways to develop efficient and cost‐effective inverted perovskite solar cells (PVSCs) is through the use of dopant‐free hole transporting materials (HTMs) with facile synthesis and a lower price tag. Herein, two organic small molecules with a fluorene core are presented as dopant‐free HTMs in inverted PVSCs, namely, FB‐OMeTPA and FT‐OMeTPA. The two molecules are designed in such a way they differ by replacing one of the benzene rings (FB‐OMeTPA) with thiophene (FT‐OMeTPA), which leads to a significantly improved coplanarity as manifested in the redshift of the absorbance and a smaller bandgap energy. Density functional theory calculations show that FT‐OMeTPA has a strong Pb²⁺–S interaction at the FT‐OMeTPA/perovskite interface, allowing surface passivation and facilitating charge transfer across interfaces. As a result, the PVSCs based on FT‐OMeTPA exhibit a much higher hole mobility, power conversion efficiency, operational stability, and less hysteresis as compared with devices based on FB‐OMeTPA.

Herein, amorphous‐Zn₂SnO₄ (am‐ZTO) is used to provide a large free energy difference (ΔG) to improve electron injection from perovskite to electron transport layers. In addition, the introduction of the am‐ZTO also leads to a dense physical contact between the am‐ZTO and the FTO substrate, leading to decreased leakage current. The optimized device exhibits a power conversion efficiency of 20.04%.

Charge extraction by electron transport layers (ETLs) plays a vital role in improving the performance of perovskite solar cells (PSCs). Here, PSCs with four different types of ETLs, such as SnO₂, amorphous‐Zn₂SnO₄ (am‐ZTO), am‐ZTO/SnO₂, and SnO₂/am‐ZTO, are successfully synthesized. The interface recombination behavior and the charge transport properties of the devices affected by four types of ETLs are systematically investigated. For dual am‐ZTO/SnO₂ ETLs, compact am‐ZTO ETL prepared by the pulsed laser deposition method provides a dense physical contact with FTO than the spin coating films, decreasing leakage current and improving charge collection at the interface of ETL/FTO. Moreover, dual am‐ZTO/SnO₂ ETLs lead to large free energy difference (ΔG), improving electron injection from perovskite to ETLs. One additional electron pathway from perovskite to am‐ZTO is formed, which can also improve electron injection efficiency. A power conversion efficiency of 20.04% and a stabilized efficiency of 19.17% are achieved for the device based on dual am‐ZTO/SnO₂ ETLs. Most importantly, the devices are fabricated at a low temperature of 150 °C, which offers a potential method for large‐scale production of PSCs, and paves the way for the development of flexible PSCs. It is believed that this work provides a strategy to design ETLs via controlling ΔG and interface contact to improve the performance of PSCs.

The changes in photophysical properties of mixed‐halide perovskite films under solar‐equivalent illumination are studied. The illumination generates localized low‐bandgap surface domains, onto which photoexcited charge carriers transfer and recombine with high radiative efficiency. The fraction of radiative and nonradiative (Auger) recombination bandgap can be balanced to achieve extremely high photoluminescence quantum yields at low excitation densities.

Abstract

Mixed‐halide lead perovskites have attracted significant attention in the field of photovoltaics and other optoelectronic applications due to their promising bandgap tunability and device performance. Here, the changes in photoluminescence and photoconductance of solution‐processed triple‐cation mixed‐halide (Cs_0.06MA_0.15FA_0.79)Pb(Br_0.4I_0.6)₃ perovskite films (MA: methylammonium, FA: formamidinium) are studied under solar‐equivalent illumination. It is found that the illumination leads to localized surface sites of iodide‐rich perovskite intermixed with passivating PbI₂ material. Time‐ and spectrally resolved photoluminescence measurements reveal that photoexcited charges efficiently transfer to the passivated iodide‐rich perovskite surface layer, leading to high local carrier densities on these sites. The carriers on this surface layer therefore recombine with a high radiative efficiency, with the photoluminescence quantum efficiency of the film under solar excitation densities increasing from 3% to over 45%. At higher excitation densities, nonradiative Auger recombination starts to dominate due to the extremely high concentration of charges on the surface layer. This work reveals new insight into phase segregation of mixed‐halide mixed‐cation perovskites, as well as routes to highly luminescent films by controlling charge density and transfer in novel device structures.

In article number https://doi.org/10.1002/aenm.2019012571901257, Yana Vaynzof and co‐workers introduce π‐extended phosphoniumfluorene electrolytes as hole‐blocking layers in planar perovskite solar cells. The electrolytes drastically alter the energetic landscape of the device, introducing a strong dipole between the fullerene electron extraction layer and the silver electrode. This results in a substantial enhancement in the built‐in potential of the device, increasing its open‐circuit voltage by up to 120 meV.

In article number https://doi.org/10.1002/aenm.2019007201900720, Yumin Liu, Li Yu, Huai Yang and co‐workers report the design of smart photovoltaic windows with a series of working modes that are enabled by coupling of multi‐responsive liquid crystal/polymer composite films and semi‐transparent perovskite solar cells, providing stable electrical power generation, energy savings, and privacy protection.