Mahui

Understanding the chemical structures of next‐generation small molecules will be a critical step for increasing the performance of organic photovoltaics (OPVs). This study reveals the importance of core structure on the device performance, and provides guidelines for the design of new materials for OPV technologies.

Understanding the chemical structures of next‐generation small molecules is a critical step for increasing the performance of organic photovoltaics (OPVs); an OPV's small molecule determines not only the extent of light absorption but also the morphology. Herein, four small molecules featuring different cores—indaceno dithiophene, dithienoindeno indaceno dithiophene (IDTT), substituted IDTT, and dithienothiophene‐pyrrolobenzothiadiazole—denoted as ID‐4Cl, IT‐4Cl, m‐ITIC‐OR‐4Cl, and Y7, respectively, are selected to form active layers with poly(quinoxaline) (PTQ10) and poly(benzodithiophene‐4,8‐dione) (PM6). The Y7 devices exhibit the best performance in both systems, with the power conversion efficiency (PCE) reaching 14.5%; in comparison, ID‐4Cl device gives a PCE of 10.0% for blending with PTQ10 and a relative efficiency enhancement of 45%. The same trend occurs for the cases of PM6 blend devices. This enhancement is attributed to i) the improved short‐circuit current density that is provided by the greater degree of conjugation in S, N‐heteroarenes ladder‐type fused‐ring cores of Y7, ii) an induced face‐on Y7 orientation and smaller domain sizes that result from the sp²‐hybridized nitrogen side chain, and iii) smaller energy loss. This study reveals the importance of the core structure on the device performance and provides guidelines for the design of new materials for OPV technologies.

1‐Naphthylmethylammonium bromide (NMABr)passivates the surface of 3D perovskite by the in situ formation of a 2D/3D type‐II heterostructure. The 2D perovskite layer blocks the transfer of electrons, reduces the trap densities, and delivers better stability. As a result, NMABr‐passivated perovskite solar cells deliver a champion efficiency of 21.09% with enhanced stability.

Heterojunction engineering is essential to reduce energy loss and enhance the stability of perovskite solar cells (PSCs). Herein, 1‐naphthylmethylammonium bromide (NMABr) is introduced to in situ generate an ultrathin p‐type 2D perovskite with wide bandgap between the 3D perovskite film and the hole transport layer (HTL). Cascade 2D/3D perovskites in situ form a type‐II heterojunction, which largely contributes to the improvement of photovoltaic performance. The type‐II heterojunction not only blocks the electron transfer and reduces the charge recombination on the surface and grain boundaries of the 3D perovskite film, but also promotes the hole extraction. The microphotoluminescence indicates the reduction of nonradiative recombination on the surface, consistent with the reduced trap density in Mott–Schottky plots and the increased recombination resistance in impedance spectra. The champion power conversion efficiency (PCE) of the NMABr‐passivated 2D/3D PSC reaches 21.09% under the AM1.5 illumination. In addition, the NMABr‐passivated 2D/3D PSC remains 80% of the initial PCE for 105 h at 85 °C in nitrogen and retains 80% of initial PCE for 350 h in 70–80% relative humidity in the air. This work provides a crucial in situ fabrication of type‐II 2D/3D heterojunction to improve the stability and efficiency of PSCs.

A novel strategy of tuning perovskite crystal orientation toward ≈45° inclination with respect to the substrate is proposed with incorporating 2,3‐diaminopropionic acid monohydrochloride (2,3‐DAPAC) into FASnI₃, which facilitates charge transport in the perovskite film from bottom to top. The solar cells with 2,3‐DAPAC acquire a champion power conversion efficiency of 7.23% and improved stability.

Despite a higher power conversion efficiency (PCE) than other lead‐free perovskite solar cells (PSCs) due to intrinsically excellent optoelectronic properties and suitable bandgaps of tin (Sn) perovskites, Sn‐based PSCs still suffer from issues of stability and efficiency for practical applications. Herein, a novel strategy of tuning perovskite crystal orientation toward ≈45° with respect to the substrate by doping 2,3‐diaminopropionic acid monohydrochloride (2,3‐DAPAC) into formamidinium tin iodide (FASnI₃) is proposed, which facilitates charge transport in the perovskite film and consequent device performances. In addition, the incorporation of 2,3‐DAPAC into FASnI₃ enables dense and smooth high‐quality perovskite films with less Sn vacancies. Applications of the 2,3‐DAPAC‐treated FASnI₃ films into PSCs acquire a champion PCE of 7.23%, showing 37.2% enhancement compared with 5.27% of the control device. Moreover, the storage stabilities of both perovskite films and PSCs are significantly prolonged with improved film quality.

A new fluorinated organic ammonium halide salt, 4‐trifluoromethyl phenethylammonium iodide (CFPEAI), is utilized to passivate the surface of CsPbI₂Br perovskite for solar cells with enhanced efficiency as well as improved stability.

Surface modification is demonstrated as an efficient strategy to enhance the efficiency and stability of perovskite solar cells (PVSCs). Fluorinated organic ammonium salts featuring a strong hydrophobic nature are seldom used as passivation agents for the surface modification of CsPbI₂Br perovskites. Herein, a fluorinated organic ammonium halide salt, 4‐trifluoromethyl phenethylammonium iodide (CFPEAI), is incorporated into the surface of CsPbI₂Br perovskite for the first time. After the CFPEAI modification, the defects of CsPbI₂Br perovskite are significantly passivated with reduced trap densities. The best‐performance PVSC with CFPEAI modification shows an excellent power conversion efficiency (PCE) of 16.07% with a high fill factor (FF) of 84.65%, a short‐circuit current density (J _SC) of 15.45 mA cm⁻², and an open‐circuit voltage (V _OC) of 1.23 V. In contrast, the control PVSCs without the surface modification exhibit a lower PCE of 14.50% with a FF of 80.56%, a J _SC of 15.05 mA cm⁻², and a V _OC of 1.20 V. With CFPEAI passivation, the CsPbI₂Br perovskite film exhibits enhanced hydrophobicity, thereby leading to improved stability for the corresponding PVSC in comparison with the control PVSC without any surface modification.

A zwitterionic conjugated polyelectrolyte presents high hole mobility, compatible covalence level, and the ability for passivating surface defects of the perovskite film. The formation of a weak double‐layer capacitance, which is not strong enough to induce the migration of MA⁺ ions, contributes to low carrier transport resistance and interfacial charge accumulation, leading to high efficiency and stability.

Achieving rapid extraction and equivalent transport of charge carriers is an effective way to improve the performance of perovskite solar cells (PSCs). Herein, a thiophene‐based zwitterionic conjugated polyelectrolyte (poly(5‐amino‐5‐carboxy‐3‐oxapentyl)‐2,5‐thiophene [POWT]) is introduced into PSCs as a hole‐transporting and interfacial material. The polyelectrolyte has a high hole mobility of 5.74 × 10⁻³ cm² V⁻¹ s⁻¹ (similar to that of poly(triarylamine) [PTAA]) and compatible covalence level relative to the perovskite. Terminated with a zwitterionic pair of a‐amino acid, POWT layer builds up a weak double‐layer capacitance at the interface, which is not strong enough to induce the migration of MA⁺ ions in the perovskite layer. Deep electrical study on the PSC with the structure of indium tin oxide (ITO)/POWT/FA_0.2MA_0.8PbI_2.9Br_0.1/C₆₀/bathocuproine (BCP)/Ag discloses that the device has low carrier transfer resistance, low leakage current density, and minor interfacial charge accumulation. The open‐circuit voltage and the short‐circuit current density are much improved, and the power conversion efficiency (PCE) is up to 17.5%. With a‐amino acid zwitterions, POWT passivates the surface charge defects and grain boundaries of the perovskite film. The PSC presents negligible hysteresis and high stability. After 56 days, the unencapsulated PSC still remains at 85% of the original efficiency.

High‐temperature degradation of perovskite solar cells with spiro‐OMeTAD hole transport layer is investigated. The postdoping of the spiro‐OMeTAD layer by iodine released from an iodine‐containing perovskite layer at high temperature is discovered as one reason for the high‐temperature degradation. Using an iodine‐free perovskite absorber, thermally stable perovskite solar cells are demonstrated.

Organic–inorganic halide perovskites are promising as the light absorber of solar cells because of their efficient solar power conversion. An issue frequently occurring in perovskite solar cells (PSCs) with a hole transport layer of N,N‐di(4‐methoxyphenyl)amino]‐9,9′‐spirobifluorene (spiro‐OMeTAD) is a quick performance degradation at high temperature. Herein, it is discovered that postdoping of the spiro‐OMeTAD layer by iodine released from the perovskite layer is one possible mechanism for the high‐temperature PSC degradation. Iodine doping leads to the highest occupied molecular orbital level of the spiro‐OMeTAD layer becoming deeper and, therefore, induces the formation of an energy barrier for hole extraction from the perovskite layer. It is demonstrated that it is possible to suppress the high‐temperature degradation by using an iodine‐blocking layer or an iodine‐free perovskite in PSCs. These findings will guide the way for the realization of thermally stable perovskite optoelectronic devices in the future.

Saddle‐shaped small molecules α, β‐COTh‐Ph‐OMeTAD and β, β‐COTh‐Ph‐OMeTAD are synthesized and systemically characterized as dopant‐free hole‐transporting material (HTM) in inverted perovskite solar cells (i‐PSCs). High power conversion efficiencies (PCEs) (17.59% and 18.53%) and stable‐enhanced PSCs devices are achieved, and more than 80% of the maximum PCE is retained after storing in glove box for 150 days.

Two saddle‐shaped hole‐transporting materials (HTMs), α, β‐COTh‐Ph‐OMeTAD and β, β‐COTh‐Ph‐OMeTAD are designed with a strategy of flexible core with tunable conformation (FCTC) and applied in inverted planar perovskite solar cells (PSCs) as dopant‐free HTMs. As a result, the device based on α, β‐COTh‐Ph‐OMeTAD demonstrates a high power conversion efficiency (PCE) of 17.59% with J _sc = 21.32 mA cm⁻², V _oc = 1.02 V, and FF = 80.75%, and the one based on β, β‐COTh‐Ph‐OMeTAD yields a higher PCE of 18.53% with J _sc = 22.68 mA cm⁻², V _oc = 1.04 V, and FF = 78.48%. Moreover, the green‐solvent‐processed PSCs are also fabricated by dissolving the HTMs in ethyl acetate. Without any encapsulation, the devices based on both HTMs retain 80% of their initial PCEs after storage for 150 days in a glove box, and 60% of their initial PCEs after storing for 300 h in ambient air with 40% relative humidity. All these results demonstrate that the materials α, β‐COTh‐Ph‐OMeTAD and β, β‐COTh‐Ph‐OMeTAD based on FCTC strategy are promising HTMs for highly efficient and stable PSCs.

A methylammonium chloride (MACl) additive is used to synthesize FA_1–x MA _x PbI₃ films. The best molar fraction of this additive is determined. The MA content in thin films actually used in solar cells is x = 0.06. This amount is thermodynamically the best for the stabilization of this highly efficient perovskite. The perovskite solar cell achieves a stabilized power conversion efficiency as high as 22.06%.

Nowadays, complex chemistry and precursor solution compositions are developed to stabilize hybrid perovskite films and boost the efficiency of perovskite solar cells (PSCs). In this context, determining the actual composition of these layers, especially in organic cations, and understanding the chemistry behind is challenging. Herein, the introduction of methylammonium (MA⁺) in formamidinium lead iodide (FAPbI₃) 3D perovskite is considered to stabilize the α‐phase, whose quantity must be minimized to reduce the material hydrophilicity and its possible destabilization by degassing. The key effects of methylammonium chloride (MACl) additive on the growth of FA_1–x MA _x PbI₃ perovskite layers are studied. Liquid nuclear magnetic resonance (NMR) is used to analyze the photovoltaic layers. NMR peaks and their origin are identified. The MA and FA content in films actually used in PSCs is reliably measured and prepared over a large additive molar concentration ratio. x is quantified at 0.06 ± 0.01 for pure films, which corresponds to the best entropic compound stabilization. It results in PSCs with a stabilized power conversion efficiency as high as 22.06%. These PSCs are shown to be highly stable under solar irradiation and high moisture.

A novel bifacial passivation strategy which simultaneously suppresses trap states within TiO₂ and perovskite through interaction between functional groups and defects is demonstrated for printable mesoscopic PSCs. The passivation treatment to TiO₂ surface not only reduces the energy barrier between TiO₂ and perovskite for accelerating the charge transfer but also passivates the uncoordinated Pb defects on the perovskite interface.

Surface defects, which mediate nonradiative recombination, are detrimental to both the photovoltaic performance and stability of perovskite solar cells (PSCs). Improving photovoltage and fill factor (FF) in screen‐printed mesoporous PSCs is a major challenge for approaching the power conversion efficiency (PCE) of the planar configured devices. Herein, a novel bifacial passivation strategy which simultaneously suppresses deep trap states within TiO₂ and perovskite through interaction between functional groups and defects is demonstrated for fully printable mesoscopic PSCs. The application of monoethanolamine (MEA) treatment to TiO₂ surface not only reduces the energy barrier between TiO₂ and perovskite for accelerating the charge transfer but also passivates the uncoordinated Pb defects on the perovskite interface. Due to the synergistic effect of charge extraction promotion and trap passivation, the fabricated PSCs deliver a champion PCE of 15.5% with an enhanced V _oc of 0.94 V and FF of 70.4% compared with PSCs without MEA passivation, and the device maintains 97% of its topmost PCE after 240 h under constant simulated solar illumination in air atmosphere. This investigation helps exploit new approaches for defect passivation to further improve both the efficiency and stability of printable mesoscopic PSCs.

The A‐D‐A′‐D‐A strategy is applied to develop two new Y6‐type unfused‐ring acceptors. The resulting fluorinated unfused acceptors lock more planar conformation, thus exhibiting red‐shifted absorption and better aggregation properties, leading to high device efficiencies of over 12%.

Unfused‐ring acceptors (UFAs) have gained considerable research attention as they offer simple chemical structures through simplified synthesis methods, which would boost the commercialization of organic solar cells (OSCs). Recently, a new small molecule acceptor (SMA) named Y6 was reported, yielding high‐performance OSCs. Herein, the Y6‐like A‐DA′D‐A framework is developed to A‐D‐A′‐D‐A‐type backbone adopted in constructing UFAs. Two new Y6‐like UFAs are synthesized within four steps and the effect of noncovalent atoms at the central electron‐deficient core on material properties and device performances is studied. It is found that the introduction of fluorine atoms can bring larger red‐shift in the absorption spectra and better aggregation of the resulting UFA film states compared with those of oxygen atoms. Interestingly, the variations in the noncovalent interaction atoms induce different intermolecular charge transfer between donors and UFAs. When blended with another economical donor, PTQ10, F substitution at the benzothiadiazole ring is more effective than O substitution, leading to the increased short‐circuit current density (J _SC) and higher efficiency of over 12%, among the best performances of UFA‐based OSCs. This contribution demonstrates the appropriate introduction of noncovalent interaction is a promising method for tuning energy levels, absorption, and aggregation of UFAs for high‐performance OSCs.

A modified monomolecular layer strategy (m‐MLS) enables high‐quality perovskite films formation on the hydrophobic polymer hole transporting layer (HTL), and minimizes the ohmic loss induced by the HTL. The perovskite solar cells (PSCs) based on m‐MLS‐modified HTL (F‐PSCs) give a superior reproducibility and a champion efficiency of 19.7% with a fill factor of over 80%.

The hole transport materials that interact with the indium tin oxide (ITO) surface can be processed into monomolecular layers (MLs), which often exhibit different surface and electronic properties than their thin‐film counterparts. Herein, it is found that poly[bis(4‐phenyl)(2,4,6‐trimethylphenyl)amine] (PTAA) films (R‐PTAA) can be easily processed into ML (M‐PTAA) due to the van der Waals interaction between ITO and PTAA. However, compared with R‐PTAA, the work function (WF) and conductivity of M‐PTAA are simultaneously reduced by the charge transfer at the ITO/PTAA interface. To address this issue, a modified monomolecular layer strategy (m‐MLS) is developed, where a small amount of 2,3,5,6‐tetrafluoro‐7,7,8,8‐tetracyanoquinodimethane (F4TCNQ) is introduced to enhance the interaction force between ITO and PTAA. PTAA treated by m‐MLS (F‐PTAA) has a hydrophilic physical surface, closely matching electronic energy level with the perovskite layer and smaller bulk resistance. As a result, the efficiency and reproducibility of perovskite solar cells (PSCs) are substantially improved. PSCs based on F‐PTAA demonstrated the highest power conversion efficiency (PCE) of 19.7% with a fill factor of over 80%. This study inspires the development of novel interface modification materials, and provides a simple and convenient direction for the fabrication of high‐performance and reproducible inverted PSCs with high fill factors.

This work discusses the fundamental understanding of the built‐in potential on efficient operation of the perovskite solar cells (PSCs) and the approach for enhancing the built‐in potential in the PSCs. The outcomes of this work are very inspiring, providing a commercially viable and cost‐effective approach for attaining high‐performance solution‐processable PSCs.

The performance of perovskite solar cells (PSCs) has been improved substantially over the past few years. However, the related fundamental understanding of improving the built‐in potential on the efficiency of the PSCs is still far from adequate. A combination of morphology, charge extraction, and built‐in potential studies would help us to gain an insight on efficient operation of the PSCs. Herein, the effect of the hybrid hole extraction layer (HEL), comprising a mixture of tungsten oxide (WO₃) and poly(3,4‐ethylenedioxythiophene)‐poly(styrenesulfonate) (PEDOT:PSS) (WO₃–PEDOT:PSS), on the growth of the perovskite photoactive layer and built‐in potential in PSCs is investigated using structural analyses, photoelectron spectroscopy, and transient photocurrent (TPC) measurements. It shows that the use of hybrid HEL is an effective approach for enhancing the built‐in potential across the photoactive layer in the PSCs, leading to >20% increase in power conversion efficiency as compared to that of a control PSC prepared using a pristine PEDOT:PSS HEL. PSCs with a higher built‐in potential are favorable for efficient cell operation, as manifested by the charge extraction analyses and TPC measurements.

All‐inorganic hole‐transport layer (HTL)‐free CsPbBr₃‐based perovskite solar cells doped with Eu²⁺ are studied. The decrement in trap‐state density and suppression of nonradiative recombination after doping is achieved with a higher power conversion efficiency (PCE) of 7.28% and V _OC of 1.45 V.

All‐inorganic perovskite of CsPbBr₃ thin‐films solar cells has attracted increasing interest in recent years due to its potential long‐term stability over the generally used hybrid perovskites. Herein, all‐inorganic CsPbBr₃ perovskites are doped with Eu²⁺ to enhance the efficiency of perovskite solar cells (PVSCs). The perovskite films exhibit a better crystallinity with smooth morphology after the introduction of rare‐earth elements. Hence, the hole‐transport layer‐free device with presence of Eu²⁺ and low‐cost carbon electrode achieves both enhanced efficiency and stability. In particular, the power conversion efficiency (PCE) enhances from 5.66% to 7.28% with high V _OC of 1.45 V by optimizing the doping concentration of Eu²⁺. In addition, the storage stability measurements reveal excellent performances of PCE without encapsulation in air with relative humidity of 70–80%. These results can pave changes in future inorganic PVSCs.

A novel perovskite‐compatible carbon electrode based on low polar alkane solvent decreases the defect at CsPbI₂Br/carbon interface and hinders moisture in the atmosphere. The champion device obtains a power conversion efficiency (PCE) of 13.16% and provides outstanding stability with a PCE maintaining 93% of the initial value after 1000 h under a humidity of 30–40% without additional encapsulation.

Carbon electrodes are a promising alternative to metal electrodes in the access of high‐stable and low‐cost perovskite solar cells (PSCs). However, polar components (including cyclohexanone, terpineol, etc.) in commercial carbon pastes for carbon electrodes usually corrode perovskite materials, thereby deteriorating the photovoltaic performance of the resulting solar cells. Therefore, the development of perovskite‐compatible carbon pastes and carbon electrodes is of great significance in obtaining high‐performance carbon‐based PSCs. Herein, carbon pastes based on low polar alkane solvents are developed for perovskite‐compatible carbon electrode (PCCE) in the construction of carbon‐based CsPbI₂Br PSCs. The optimized cells based on PCCE offer a champion efficiency of 13.16% (J _SC = 14.33 mA cm⁻², V _OC = 1.22 V, and fill factor (FF) = 0.75), which is remarkably higher than that of commercial carbon paste‐derived counterparts (11.51%). Even without encapsulation, CsPbI₂Br PSCs based on PCCE maintain over 93% of their initial efficiency in an air atmosphere with a humidity of 30–40% for over 1000 h.

Efficient ternary blend nonfullerene organic solar cells based on two polymer donors and one fused‐ring electron acceptor are fabricated. The fine‐tuning blend morphology and reduced nonradiative energy loss in this ternary system enable achievement of a power conversion efficiency of over 16%, which is among the highest values for ternary organic solar cells with two polymer donors.

High‐performance nonfullerene ternary organic solar cells (OSCs) with two polymer donors are less frequently reported because of the limited numbers of efficient polymer donors with good compatibility. Herein, a wide‐bandgap polymer P1 with a deep‐lying highest occupied molecular orbital (HOMO) level is incorporated as the third component into the benchmark PM6:Y6 binary system to fabricate ternary OSCs. The introduction of P1 not only leads to extended absorption coverage and forms a cascade‐like energy level alignment but also shows excellent compatibility with PM6, resulting in a favorable morphology in the ternary blend. More importantly, P1 possesses a deeper HOMO level (−5.6 eV) than most well‐known donor polymers, which enables resulting ternary OSCs with an improved open‐circuit voltage. As a result, the optimized ternary OSCs with 40 wt% P1 in donors achieve a power conversion efficiency (PCE) of 16.2% with a small nonradiative recombination loss of 0.23 eV, which is among the highest values of ternary OSCs based on two polymer donors. In addition, the ternary OSCs show a broad composition tolerance with a high PCE of over 14% throughout the whole blend ratios. These results provide an effective approach to fabricate efficient ternary OSCs by synergizing two wide‐bandgap polymer donors.

Ternary organic solar cells (TOSCs) are developed through synergizing small‐molecule donor BPR‐SCl into PM6:Y6 host binary blend, which effectively addresses the trade‐off between photovoltage and photocurrent of regular bulk heterojunction OSCs. An optimal power conversion efficiency of 16.74% is obtained for TOSCs, accounting for 10% and 70% improvements over those of pristine PM6:Y6 and BPR‐SCl:Y6 binary devices, respectively.

Despite the impressive progress that has been achieved for organic solar cells (OSCs) in recent years, challenges remain for OSCs due to the presence of the trade‐off between photovoltage and photocurrent that sets limitation on the performance enhancement of regular bulk heterojunction (BHJ) blends. Herein, a new small‐molecule (SM) donor, BPR‐SCl, with the deep‐lying highest occupied molecular orbital and strong crystallinity has been developed, which, as the third component, is synergized with PM6:Y6 host blend. The introduction of BPR‐SCl enhances molecular packing, exciton dissociation, as well as charge mobilities of ternary blends, yielding simultaneous enhancement of open‐circuit voltage, short‐circuit current density, and fill factor of ternary OSCs (TOSCs). As a result, an optimal power conversion efficiency (PCE) of 16.74% is obtained for TOSCs with 25 wt% BPR‐SCl, accounting for 10% and 70% improvements over those of pristine PM6:Y6 and BPR‐SCl:Y6 binary devices, respectively. Overall, herein, it is demonstrated that the design of SM donor as the third component is effective in achieving high‐performance TOSCs.

Antisolvent engineering is employed to tune the crystal nucleation and grain growth of perovskite for achieving efficient perovskite solar cells. The engineering of perovskites treated with the green antisolvent MABr‐Eth, suppressing defects‐induced nonradiative recombination in perovskite solar cells, is developed. As expected, the device delivers over 21% power conversion efficiency and a better storage and light‐soaking stability.

Abstract

Organic–inorganic hybrid perovskites have attracted considerable attention due to their superior optoelectronic properties. Traditional one‐step solution‐processed perovskites often suffer from defects‐induced nonradiative recombination, which significantly hinders the improvement of device performance. Herein, treatment with green antisolvents for achieving high‐quality perovskite films is reported. Compared to defects‐filled ones, perovskite films by antisolvent treatment using methylamine bromide (MABr) in ethanol (MABr‐Eth) not only enhances the resultant perovskite crystallinity with large grain size, but also passivates the surface defects. In this case, the engineering of MABr‐Eth‐treated perovskites suppressing defects‐induced nonradiative recombination in perovskite solar cells (PSCs) is demonstrated. As a result, the fabricated inverted planar heterojunction device of ITO/PTAA/Cs_0.15FA_0.85PbI₃/PC₆₁BM/Phen‐NADPO/Ag exhibits the best power conversion efficiency of 21.53%. Furthermore, the corresponding PSCs possess a better storage and light‐soaking stability.

High‐performance semitransparent organic solar cells are achieved through combined design efforts on the formulation of near‐infrared ternary blends and optical control over photonic reflectors, which exhibit excellent features of power generation, they being see‐through, and infrared reflection.

Abstract

Clean energy production and saving play vital impacts on the sustainability of the global community. Herein, high‐performance semitransparent organic solar cells (ST‐OSCs) with excellent features of power generation, being see‐through, and infrared reflection of heat dissipation, with promising perspectives for building‐integrated photovoltaics (BIPVs) are reported. To simultaneously improve average visible transmittance (AVT) and power conversion efficiency (PCE), formally in a trade‐off relationship, of ST‐OSCs, new ternary blends with alloy‐like near‐infrared (NIR) acceptors are employed, which are effective to improve device efficiency while maintaining visible absorption unchanged, resulting in PCEs of 16.8% for opaque devices and 13.1% for semitransparent OSCs (AVT of 22.4% and infrared photon radiation rejection (IRR) of 77%). Further, multifunctional ST‐OSCs are realized via introducing simple, yet effective photonic reflectors, together with optical simulation, leading to not only perfect fitting of the visible transmittance peak (555 nm) to the photopic response of the human eye but also an excellent IRR of 90% (780–2500 nm), along with 23% AVT and over 12% PCE. This is thought to be the best‐performing multifunctional ST‐OSC with promising prospects as BIPVs in terms of power generation, heat dissipation, and being see‐through.

A formamidinium (FA)‐based quasi‐2D Ruddlesden–Popper (RP) perovskite, namely, (ThMA)₂(FA) _{n −1}Pb _n I_{3 n +1} (nominal n = 5), is successfully demonstrated with high photovoltaic performance by using an organic‐salt‐assisted crystal growth method. The optimized device exhibits a champion efficiency of 19.06%, which is a record for quasi‐2D RP perovskite solar cells with nominal n‐value lower than 6.

Abstract

Quasi‐2D Ruddlesden–Popper (RP) perovskite solar cells (PSCs) have drawn significant attention due to their appealing environmental stability compared to their 3D counterparts. However, the relatively low power conversion efficiency (PCE) greatly limits their applications. Here, high photovoltaic performance is demonstrated for quasi‐2D RP PSCs using 2‐thiophenemethylammonium as spacer with nominal n‐value of 5, which is based on the stoichiometry of the precursors. The incorporation of formamidinium (FA) in quasi‐2D RP perovskites reduces the bandgap and improves the light absorption ability, resulting in enlarged photocurrent and an increased PCE of 16.18%, which is higher than that of reported analogous methylammonium (MA)‐based quasi‐2D PSC (≈15%). A record high PCE of 19.06% is further demonstrated by using an organic salt, namely, 4‐(trifluoromethyl)benzylammonium iodide, assisted crystal growth (OACG) technique, which can induce the crystal growth and orientation, tune the surface energy levels, and suppress the charge recombination losses. More importantly, the devices based on OACG‐processed quasi‐2D RP perovskites show remarkable environmental stability and thermal stability, for example, the PCE retaining ≈96% of its initial value after storage at 80 °C for 576 h, while only ≈37% of the original efficiency left for FAPbI₃‐based

3D PSCs.

A unique strategy of “transparent hole‐transporting frameworks” is proposed. A hole‐transporting large‐bandgap polymer, PTAA, is employed to partially replace the polymer donors in the active layer. As a result, semitransparent organic photovoltaic devices with power conversion efficiencies ≈12% and average visible transmittances ≈20% are achieved both on rigid and flexible substrates.

Abstract

Thanks to the nature of molecular orbitals, the absorption spectra of organic semiconductors are not continuous like those in traditional inorganic semiconductors, which offers a unique application of organic photovoltaics (OPVs): semitransparent OPVs. Recently, the exciting progress of materials design has promoted the development of semitransparent OPVs. However, in the perspective of device engineering, almost all reported works reduce the thickness of back/reflected electrode to obtain high average visible transmittance (AVT), which is a trade‐off between power conversion efficiency (PCE) and the transmittance of the whole solar spectrum (visible and infrared), and therefore limit the further development. Herein, a unique strategy of “transparent hole‐transporting frameworks” is proposed. A hole‐transporting large‐bandgap polymer (poly[bis(4‐phenyl)(2,4,6‐trimethylphenyl)amine (PTAA)) is employed to partially replace polymer donors in the active layer of PBDB‐T/Y1. PTAA is a p‐type polymer with a large bandgap of 2.9 eV; the partial substitution of PBDB‐T by PTAA reduces the absorption of the active layer only in the visible region, keeping the hole‐transporting pathways as well as the optimized film morphology. As a result, semitransparent OPVs with PCEs of 12% and AVTs of 20% are achieved, both on rigid and flexible substrates. To demonstrate the generality, this strategy is also used in three different active layers.

Introduction of multi‐cation hybrid halide perovskite quantum dots reduces ionic defects at the surface and grain boundaries via a solid‐state interdiffusion process. The enhanced moisture and photostability enable power conversion efficiency (PCE) exceeding 21% to be achieved with more than 90% of its initial PCE retained on exposure to continuous illumination of more than 550 h.

Abstract

Realization of reduced ionic (cationic and anionic) defects at the surface and grain boundaries (GBs) of perovskite films is vital to boost the power conversion efficiency of organic–inorganic halide perovskite (OIHP) solar cells. Although numerous strategies have been developed, effective passivation still remains a great challenge due to the complexity and diversity of these defects. Herein, a solid‐state interdiffusion process using multi‐cation hybrid halide perovskite quantum dots (QDs) is introduced as a strategy to heal the ionic defects at the surface and GBs. It is found that the solid‐state interdiffusion process leads to a reduction in OIHP shallow defects. In addition, Cs⁺ distribution in QDs greatly influences the effectiveness of ionic defect passivation with significant enhancement to all photovoltaic performance characteristics observed on treating the solar cells with Cs_0.05(MA_0.17FA_0.83)_0.95PbBr₃ (abbreviated as QDs‐Cs5). This enables power conversion efficiency (PCE) exceeding 21% to be achieved with more than 90% of its initial PCE retained on exposure to continuous illumination of more than 550 h.

The inclusion of a novel in situ polymerizable ionic liquid, 1,3‐bis(4‐vinylbenzyl)imidazolium chloride ([bvbim]Cl), allows perovskite films to be manufactured under humid environments, conferring improved materials quality, higher power conversion efficiency, and long‐term stability.

Abstract

Despite the excellent photovoltaic properties achieved by perovskite solar cells at the laboratory scale, hybrid perovskites decompose in the presence of air, especially at high temperatures and in humid environments. Consequently, high‐efficiency perovskites are usually prepared in dry/inert environments, which are expensive and less convenient for scale‐up purposes. Here, a new approach based on the inclusion of an in situ polymerizable ionic liquid, 1,3‐bis(4‐vinylbenzyl)imidazolium chloride ([bvbim]Cl), is presented, which allows perovskite films to be manufactured under humid environments, additionally leading to a material with improved quality and long‐term stability. The approach, which is transferrable to several perovskite formulations, allows efficiencies as high as 17% for MAPbI₃ processed in air % relative humidity (RH) ≥30 (from an initial 15%), and 19.92% for FAMAPbI₃ fabricated in %RH ≥50 (from an initial 17%), providing one of the best performances to date under similar conditions.

Ambipolar black phosphorene (BP) nanosheets with tailored thicknesses concurrently enhance carrier extraction at both the electron‐transport layer/perovskite and hole‐transport layer/perovskite interfaces for high‐efficiency perovskite solar cells, demonstrating the appealing implementation of BP as a dual‐functional carrier‐transport material for a diversity of optoelectronic devices, including solar cells, photodetectors, sensors, light‐emitting diodes, etc.

Abstract

2D black phosphorene (BP) carries a stellar set of physical properties such as conveniently tunable bandgap and extremely high ambipolar carrier mobility for optoelectronic devices. Herein, the judicious design and positioning of BP with tailored thickness as dual‐functional nanomaterials to concurrently enhance carrier extraction at both electron transport layer/perovskite and perovskite/hole transport layer interfaces for high‐efficiency and stable perovskite solar cells is reported. The synergy of favorable band energy alignment and concerted cascade interfacial carrier extraction, rendered by concurrent positioning of BP, delivered a progressively enhanced power conversion efficiency of 19.83% from 16.95% (BP‐free). Investigation into interfacial engineering further reveals enhanced light absorption and reduced trap density for improved photovoltaic performance with BP incorporation. This work demonstrates the appealing characteristic of rational implementation of BP as dual‐functional transport material for a diversity of optoelectronic devices, including photodetectors, sensors, light‐emitting diodes, etc.

Judicious incorporation of ambiopolar black phosphorene with tailored thickness to concurrently impart electron and hole extractions in perovskite solar cells is reported by Jinsong Huang, Zhiqun Lin, and co‐workers in article number https://doi.org/10.1002/adma.2020009992000999. This work underpins the potential implementation of black phosphorene as a dual‐functional transport material for a diversity of optoelectronic devices, including photodetectors, sensors, and light‐emitting diodes.

A highly efficient organic solar cell with a ternary architecture is successfully demonstrated by enhancing and balancing charge transport as well as matching integer charge transfer energy in a bulk heterojunction blend. As a result, a power conversion efficiency of 17.13% is obtained with the significantly improved fill factor of 0.813.

Abstract

Ternary architecture is one of the most effective strategies to boost the power conversion efficiency (PCE) of organic solar cells (OSCs). Here, an OSC with a ternary architecture featuring a highly crystalline molecular donor DRTB‐T‐C4 as a third component to the host binary system consisting of a polymer donor PM6 and a nonfullerene acceptor Y6 is reported. The third component is used to achieve enhanced and balanced charge transport, contributing to an improved fill factor (FF) of 0.813 and yielding an impressive PCE of 17.13%. The heterojunctions are designed using so‐called pinning energies to promote exciton separation and reduce recombination loss. In addition, the preferential location of DRTB‐T‐C4 at the interface between PM6 and Y6 plays an important role in optimizing the morphology of the active layer.

A highly efficient organic solar cell with a ternary architecture is successfully demonstrated by enhancing and balancing charge transport as well as matching integer charge transfer energy in a bulk heterojunction blend. As a result, a power conversion efficiency of 17.13% is obtained with the significantly improved fill factor of 0.813.

Abstract

Ternary architecture is one of the most effective strategies to boost the power conversion efficiency (PCE) of organic solar cells (OSCs). Here, an OSC with a ternary architecture featuring a highly crystalline molecular donor DRTB‐T‐C4 as a third component to the host binary system consisting of a polymer donor PM6 and a nonfullerene acceptor Y6 is reported. The third component is used to achieve enhanced and balanced charge transport, contributing to an improved fill factor (FF) of 0.813 and yielding an impressive PCE of 17.13%. The heterojunctions are designed using so‐called pinning energies to promote exciton separation and reduce recombination loss. In addition, the preferential location of DRTB‐T‐C4 at the interface between PM6 and Y6 plays an important role in optimizing the morphology of the active layer.