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Publication date: July 2021

Source: Nano Energy, Volume 85

Author(s): Qi Liu, Yang Wang, Jin Fang, Haiqin Liu, Lei Zhu, Xia Guo, Mengyuan Gao, Zheng Tang, Long Ye, Feng Liu, Maojie Zhang, Yongfang Li

A solution‐based passivation strategy focusing on near‐surface defects is explored for CuInS₂ absorbers grown under Cu‐excess conditions. The impact of near‐surface defects, similar to Cu‐rich selenides, on the device performance is investigated. A model for explaining electrical characteristics is evoked. Results of sulfur‐based treatment using thiourea solution as the sulfur source record an improvement in device performance.

Interface recombination at the absorber surface impedes the efficiency of a solar cell with an otherwise excellent absorber. The internal voltage or quasi‐Fermi‐level splitting (qFLs) measures the quality of the absorber. Interface recombination reduces the open‐circuit voltage (V _OC) with respect to the qFLs. A facile solution‐based sulfur postdeposition treatment (S‐PDT) is explored to passivate the interface of CuInS₂ grown under Cu‐rich conditions, which show excellent qFLs values, but much lower V _OCs. The absorbers are treated in S‐containing solutions at 80 °C. Absolute calibrated photoluminescence and current–voltage measurements demonstrate a reduction of the deficit between qFLs and V _OC by almost one‐third compared with the untreated device. Temperature dependence of the open‐circuit voltage shows increased activation energy for the dominant recombination path, indicating less interface recombination. In addition, capacitance transients reveal the presence of slow metastable defects in the untreated solar cell. The slow response is considerably reduced by the S‐PDT, suggesting passivation of these slow metastable defects. The results demonstrate the effectiveness of solution‐based S‐treatment in passivating defects, presenting a promising strategy to explore and reduce defect states near the interface of chalcogenide semiconductors.

Transient optical spectroscopy is used to study the temperature dependence of exciton dissociation and free charge generation dynamics in two model nonfullerene organic solar cell blends: P3TEA:SF‐PDI₂ and PM6:Y6. The results suggest that overcoming the Coulomb barrier for interfacial charge separation is the main reason for the endothermic charge separation observed for these material systems, instead of diffusion‐limited exciton dissociation.

Organic solar cells based on nonfullerene acceptor molecules show high charge generation yields with negligible driving force at the donor–acceptor (D/A) interface to drive exciton dissociation. Understanding the underlying charge generation dynamics in these material systems is crucial for further development of this technology. Herein, the acceptor exciton dissociation dynamics in these materials is studied using transient optical spectroscopy. The results show that exciton dissociation at the D/A interface takes up to ≈100 ps to complete, and this process is not significantly affected by temperature. A similar timescale for charge transfer (CT) state separation into free electrons and holes is observed at room temperature. But in contrast to the weak temperature dependence of exciton dissociation, the free charge generation rate and yield are significantly reduced at low temperature. This suggests that overcoming the Coulomb barrier for charge separation at the D/A interface is the main reason for the endothermic charge separation observed for these material systems, instead of diffusion‐limited exciton dissociation.

An SnS homojunction solar cell is fabricated for the first time by the deposition of p‐type polycrystalline thin films on n‐type single crystals. The cell shows an open‐circuit voltage (V _OC) of 360 mV and a conversion efficiency of 1.4%. The high V _OC (≈the highest V _OC of previously reported SnS‐based heterojunction cells) reveals the potential of the homojunction solar cells.

Herein, a pn homojunction SnS solar cell is fabricated for the first time by the deposition of p‐type SnS polycrystalline thin films on the recently reported large n‐type SnS single crystals. The p‐type thin films consist of columnar grains that grow along the <100> direction, which is the same orientation as the n‐type single crystal. In addition, the interface of the pn homojunctions is void‐free and compositionally sharp. The SnS homojunction solar cell achieves an open‐circuit voltage (V _OC) of 360 mV, which is as large as the highest V _OC of previously reported SnS‐based heterojunction solar cells. The built‐in potential of the homojunction cell is 0.92 eV, which is close to the bandgap energy of SnS (≈1.1 eV), and larger than reported for heterojunctions (≈0.7 eV). The resulting 1.4% conversion efficiency (η) of the homojunction solar cell is smaller than the record 4–5% in heterojunctions, mainly due to the low short‐circuit current density (J _SC) of 7.5 mA cm⁻². Once the device structure of the homojunction cell is optimized to efficiently collect the photogenerated carriers and achieve a comparable J _SC as the conventional heterojunction cells (≈25 mA cm⁻²), high η exceeding 4–5% will be realized with improving the V _OC.

The alkylated reduced graphene oxide (AF‐rGO) is well dispersed in nonpolar solvents; thus, it is successfully coated on top of the perovskite layer as a hole transport layer (HTL) through a solution process. An AF‐rGO‐based planar n‐i‐p perovskite solar cell (PeSC) shows the highest efficiency among the planar n‐i‐p PeSC using graphene materials as the sole HTL.

Reduced graphene oxides (rGOs), despite their excellent electrical properties, have been seldom used as the solution‐processed sole hole transport material (HTM) in perovskite solar cells (PeSCs) with an n‐i‐p structure, due to their low dispersity in orthogonal solvent of perovskite, such as chlorobenzene (CB). The limited rGO dispersion in nonpolar solvents precludes the formation of a fully covered film on top of the perovskite layer. A newly designed alkylated rGO (AF‐rGO) is synthesized, which can be highly dispersed in a nonpolar solvent, for use as a solution‐processed HTM on top of the perovskite layer in PeSCs. The AF‐rGO can be dispersed in CB at a high concentration, and a fully covered AF‐rGO film is successfully introduced on top of the perovskite layer as HTM through a simple solution process. The AF‐rGO in the PeSC exhibits minimal series resistance and charge recombination and exhibits efficient hole extraction and transport abilities, resulting in a maximum power conversion efficiency (PCE) of 17%, which is the highest PCE of PeSCs with an n‐i‐p structure, which use graphene‐based materials as the sole HTM. Moreover, devices with AF‐rGO HTM exhibit improved ambient stability, exhibiting 89% of their original performance after 240 h of storage without encapsulation.

2D Ti₃C₂T _x nanosheets are fabricated and incorporated into the active layer of devices as a third component to obtain an enhancement of the photovoltaic device performance. The optimized devices based on PBDB‐T:ITIC@Ti₃C₂T _x and PM6:Y6@Ti₃C₂T _x reach a power conversion efficiency of 10.72% and 16.25%, respectively.

Solution‐processed 2D Ti₃C₂T _x nanosheets are incorporated into the active layer of organic solar cells (OSCs) as a third component to obtain an enhancement of the photovoltaic device performance. The power conversion efficiency (PCE) of the devices is boosted from 9.34% to 10.72% for the PBDB‐T:ITIC blend and from 14.64% to 16.25% for the PM6:Y6 blend after adding 2D Ti₃C₂T _x nanosheets. The light scattering of the 2D flakes in Ti₃C₂T _x nanosheets not only increases the short‐circuit current density (J _SC) but also improves the carrier dissociation and transfer efficiency in devices, thus leading to reduced bimolecular recombination. Furthermore, Ti₃C₂T _x with appropriate content has little effect on the interpenetrating network morphology and instead provides an additional pathway for charge transport in photoactive layers. Herein, a potential direction for the application of 2D Ti₃C₂T _x materials in the field of OSCs is provided.

A modified two-step sequential deposition method is proposed to prepare the CsRb-based multi-cation perovskite film. The method provides fine control over the processes of crystal nucleation and grain growth, resulting in high-quality, large-grained perovskite films, and leads to efficient perovskite solar cells with high reproducability.

High-quality perovskite films with low defect densities and high carrier-diffusion lengths are essential for high-performance perovskite devices. Herein, a modified two-step sequential method is proposed, in which equal amounts of Cs⁺ and Rb⁺ ions (Cs⁺Rb⁺) are added to a PbI₂ solution in the first step of perovskite deposition. The incorporation of Cs⁺Rb⁺ results in trace amounts of δ-CsPbI₃, leading to a reduction in the grain size in the PbI₂ layer that facilitates better penetration of the organic salts in the second step of the precursor deposition. Meanwhile, the low density of the δ-CsPbI₃ crystals act as seeds to regulate the nucleation and growth of the perovskite crystals. A single-layered columnar large-grain perovskite film is obtained. The addition of Cs⁺Rb⁺ promotes crystal growth along the (100) orientation, which is beneficial for the reduction of surface defects. The incorporated Rb⁺ ions can regulate the remaining PbI₂ in the perovskite. The improved quality of the perovskite film results in a significantly prolonged carrier lifetime of ≈7.01 μs and an enhanced electron diffusion length of ≈2.84 μm. As a result, the photovoltaic parameters are all improved in the established devices and a power conversion efficiency of 21.49% is reached.

Non‐fullerene organic solar cells without 1,8‐Diiodooctane additive are found to degrade with a self‐doping increase toward the interfaces, whereas the concentration of recombination centers homogeneously increase along the active layer. The study comprises monitoring current–voltage curves during in situ photostability tests, impedance spectroscopy under illumination at open‐circuit and in dark via Mott–Schottky analysis, and drift–diffusion numeric simulations.

Non‐fullerene‐based organic solar cells (OSCs) have recently proven to perform with efficiencies above 18%. This is an important milestone for one of the most promising technologies in the fields of flexible and transparent/semitransparent photovoltaics. However, the stability of OSCs is still a challenging issue to meet the industry requirements. Herein, several devices with IT‐4F:PM6 as the active layer with and without 1,8‐Diiodooctane (DIO) additive are characterized before and after a 1400 h degradation test under 1 sun white light‐emitting diode (LED) illumination intensity. The optoelectronic study via impedance spectroscopy under illumination at quasi‐open‐circuit correlates the use of DIO as an additive with a retarded degradation behavior and an overall improved device performance. In dark conditions, the Mott–Schottky analysis suggests that samples without DIO develop self‐doping during degradation, changing the p‐i‐n doping profile into a p–n type, most likely related to the evolution of the blend demixing. These mechanisms are further confirmed by drift‐diffusion simulations. Space‐oriented redistribution of shallow trap levels (self‐doping) and homogeneous increase in deep‐trap levels (nonradiative recombination) are shown to be hindered by the use of the DIO additive.

An aromatic diammonium cation p‐phenyl dimethylammonium iodide is applied to facilitate the formation of Dion−Jacobson phase‐based quasi‐2D perovskites at the grain boundaries. Due to passivating defect and suppressing Sn²⁺ oxidation, the trap density of the perovskite film decreases by one order of magnitude. Consequently, the Pb–Sn mixed narrow‐bandgap perovskite solar cells achieve an efficiency of 20.5% and exhibit great stability.

The mixed Pb–Sn perovskites have the ideal bandgap of ≈1.2 eV for photovoltaic application. However, the undesirable p‐doping introduced by Sn²⁺ oxidation restrains the device's power conversion efficiency (PCE) and stability. Herein, an additive strategy with p‐phenyl dimethylammonium iodide (PhDMADI) is proposed, which has a bulky divalent organic cation and facilitates the formation of Dion–Jacobson phase‐based quasi‐2D perovskites at the grain boundaries. It is found that this unique 2D/3D bulk heterojunction structure is beneficial to suppress the oxidation of Sn²⁺ and isolate the moisture and oxygen, resulting in a good stability of the solar cell. Moreover, the quasi‐2D perovskites can passivate defects effectively. The trap density of the perovskite film has decreased by one order of magnitude, thus the carrier lifetime is increased more than twice. These enhanced properties enable us to fabricate a device of 20.5% PCE with great stability.

A hollow and compressible photothermal evaporator is designed and fabricated to realize portable solar steam generation without any energy loss. An extremely high evaporation rate of 7.6 kg m⁻² h⁻¹ with a corresponding energy efficiency far beyond the theoretical limit is achieved. The evaporator can be compressed for easy storage.

Solar steam generation offers a sustainable strategy to mitigate global clean water scarcity. To this end, 3D photothermal evaporators have attracted increasing research interest since they can significantly improve both evaporation rate and energy efficiency. However, compared to the 2D evaporators, the 3D ones consume more raw materials and occupy more storage space, which limits their applications for practical portable solar steam generation. To address this issue, a 3D hollow and compressible photothermal evaporator is designed and fabricated which can be compressed to less than one third of its original volume, thus enabling easier transport and storage. Moreover, under 1.0 sun illumination, all evaporation surfaces of this 3D evaporator are lower in temperatures than the surrounding environment, thus providing the unique advantage of zero energy loss to the environment during solar evaporation. Due to the all-cold evaporation surfaces, during solar evaporation, the evaporator is able to harvest massive energy from both the surrounding air and bulk water, delivering an extremely high evaporation rate of up to 7.6 kg m⁻² h⁻¹ under 1.0 sun irradiation. Furthermore, seawater desalination tests demonstrate that the device has great potential for portable solar thermal desalination by delivering clean water with a salinity well below 50 ppb.

Herein, solution-processed copper-doped chromium oxide (Cu:CrO _x ) films with tunable oxygen vacancy are demonstrated via a postannealing process. The properties of solution-processed Cu:CrO _x films annealed at different temperatures are characterized, showing that the average cation oxidation states and the work function of the Cu:CrO _x films have a strong dependence on the postannealing temperature.

Compared with vacuum evaporation, metal oxides deposited by solution process exhibit advantages, for example, dopants can be easily incorporated in a wide range and the contents are easy to be regulated by changing the composition of precursors. Herein, solution-processed p-type copper-doped chromium oxide (Cu:CrO _x ) films with tunable oxygen vacancy are demonstrated via a postannealing process. The synthetic and postannealing temperature have a significant impact on the chromium cation oxidation state in the Cu:CrO _x films, leading to the variation of work function for the oxide films. By adjusting the work function of Cu:CrO _x films, a low contact resistivity of 95 mΩ cm² can be realized for the Ag/Cu:CrO _x /p-Si contact. Finally, the optimized Cu:CrO _x films are used as the hole transporting layer in c-Si solar cells, showing an increased power conversion efficiency from 15.2% (without Cu:CrO _x ) to 16.9% (with Cu:CrO _x ). The results show an effective stage to use p-type metal oxides as a hole-selective layer in c-Si solar cells.

A dual function interfacial layer is proposed with p-type dopant, tetrafluoro-tetracyanoquinodimethane (F4TCNQ), which induces a favorable energy level alignment and passivated contacts between the hole transport layer and perovskite layer. The optimized device achieves an improved power conversion efficiency of 8.11% compared with the pristine solar cell.

Interfacial engineering plays a key role for the stability and efficiency of perovskite photovoltaics, especially for the tin perovskite solar cells (TPSCs). Herein, a simple and effective interfacial layer approach to modify the heterointerface between hole transport layer (HTL) and perovskite active layer is reported. By the deposition of a p-type dopant, tetrafluoro-tetracyanoquinodimethane (F4TCNQ) onto the commonly used poly(3,4-ethylenedioxythiophene)-poly(styrenesulfonate) (PEDOT:PSS) HTL, a favorable energy level alignment with the mixed-cation tin perovskite is obtained. Moreover, the F4TCNQ interfacial layer introduces a passivated contact and suppressed trap density at the HTL/perovskite interface through halogen bonding. As a result, the optimized TPSC yields an improved efficiency of 8.11% as compared with 6.41% of the reference device. Meanwhile, the stability of the TPSC is also improved due to the hydrophobicity of the F4TCNQ interfacial layer. This work demonstrates that the incorporation of an interfacial layer at the HTL/perovskite interface is a feasible approach to boost the efficiency and stability of inverted TPSC.

Herein, the requirements for making nonfullerene acceptor-based solar cells with thick active layers and high efficiencies are clarified. A combined electro-optical device model is used to determine the effect on the efficiency of varying the charge carrier mobilities, doping concentration, and recombination pre-factor. The results show that a mobility imbalance and doping can lead to improved performance at large thicknesses.

Organic bulk-heterojunction solar cells based on the newly developed nonfullerene electron acceptors have the potential for very low-cost energy production. However, to enable large-scale production with common printing techniques, the active layer thicknesses need to be increased by up to an order of magnitude, which is currently not possible without significant loss in performance. Herein, the requirements for making nonfullerene acceptor (NFA)-based solar cells with thick active layers and high efficiencies are clarified. The charge carrier mobility, unintentional doping concentrations, and bimolecular recombination prefactor in the model high-efficiency system PM6 (Poly[(2,6-(4,8-bis(5-(2-ethylhexyl-3-fluoro)thiophen-2-yl)-benzo[1,2-b:4,5-b′]dithiophene))-alt-(5,5-(1′,3′-di-2-thienyl-5′,7′-bis(2-ethylhexyl)benzo[1′,2′-c:4′,5′-c′]dithiophene-4,8-dione)]):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) are determined. The results are implemented in a combined electro-optical device model, which is used to determine the effect of varying these parameters on the efficiency. The results show that a mobility imbalance and doping can lead to improved performance at large thicknesses, partially contradicting previous studies performed on fullerene-based systems. The findings highlight the importance of determining electron and hole mobilities selectively, as well as characterizing recombination and doping concentrations.

Various polymers and 1D polymer-like materials are added to perovskite precursor solutions to increase perovskite solar cell efficiency and device stability. Correlations between key material properties and device performance are chronologically discussed and summarized according to material type.

Polymers or polymeric materials are used as additives for promoting the nucleation and crystallization of perovskite films to increase the crystal grain size. Due to their high molecular weight, polymers remain within perovskite-crystal grain boundaries (GBs), where they passivate trap sites. Furthermore, some polymers function as charge-transport materials in interfacial layers to effectively separate charge carriers and reduce charge recombination. Certain hydrophobic polymers protect perovskite films against moisture, whereas elastic polymers contribute to the mechanical resilience of perovskite films by crosslinking and self-healing. Although polymeric additives have become essential to perovskite fabrication, a thorough review has not summarized their application to perovskite solar cells. Therefore, various strategies are comprehensively discussed for incorporating typical polymers and 1D polymeric materials into perovskite materials to improve the efficiency and stability of perovskite devices. Herein, thermoplastic, hydrophilic, and conductive polymers and elastomers are focused and related works are chronologically discussed to clearly elucidate the advances in perovskite devices.

The application of additive engineering in tin perovskite solar cells is reviewed, from the aspects of the structures and properties of tin perovskite, additives used for stabilizing divalent Sn²⁺, purifying the tin source to improving the crystalline quality. In addition, challenges and perspectives are proposed to promote the performance of tin perovskite solar cells.

Perovskite solar cells (PSCs) have emerged as one of the third-generation photovoltaic technologies. However, the toxicity issue of the lead element in perovskite absorbers hinders their large-scale production. Thus, exploiting lead-free perovskite materials becomes an important solution to overcome this challenge. Among all the candidates, tin perovskites have advanced rapidly in recent years due to their low toxicity, favorable bandgap, and high carrier mobility. After a few years of development, the highest power conversion efficiency (PCE) of tin PSCs has exceeded 13%, which is mainly attributed to the breakthroughs arising from additive engineering of the Sn perovskite layer. Herein, the role of additive engineering in the research community of tin PSCs is emphasized. First, the crystal structure, electronic characteristics, and the chemical instability of Sn perovskites are introduced. Next, additives used for stabilizing the Sn²⁺ components, purifying SnI₂ sources, and improving the crystal quality of perovskite films are discussed in detail. Finally, challenges and perspectives are laid out to advance the properties of tin halide perovskites for further improving the device efficiency and stability.

Publication date: 21 April 2021

Source: Joule, Volume 5, Issue 4

Author(s): Tao Liu, Tao Yang, Ruijie Ma, Lingling Zhan, Zhenghui Luo, Guangye Zhang, Yuan Li, Ke Gao, Yiqun Xiao, Jianwei Yu, Xinhui Zou, Huiliang Sun, Maojie Zhang, Top Archie Dela Peña, Zengshan Xing, Heng Liu, Xiaojun Li, Gang Li, Jianhua Huang, Chunhui Duan

Publication date: 17 March 2021

Source: Joule, Volume 5, Issue 3

Author(s): Lujia Xu, Wenzhu Liu, Haohui Liu, Cangming Ke, Mingcong Wang, Chenlin Zhang, Erkan Aydin, Mohammed Al-Aswad, Konstantinos Kotsovos, Issam Gereige, Ahmed Al-Saggaf, Aqil Jamal, Xinbo Yang, Peng Wang, Frédéric Laquai, Thomas G. Allen, Stefaan De Wolf

Perovskite Solar Cells In their Communication on page 6294, Jing Cao et al. report the preparation of a nickel phthalocyanine decorated with four methoxyethoxy units and its application as a hole‐transporting material in perovskite solar cells.

Hexyltrimethylammonium bromide modification of the CsPbI₂Br film improved the energy level mismatch, the hole transformation at the CaPbI₂Br/carbon electrode interface, and suppressed charge recombination in devices. Combined with the high‐quality thick perovskite films (up to 800 nm), a champion efficiency of 14.3% and a new certified efficiency record of 14.0% are obtained for carbon‐based all‐inorganic perovskite solar cells.

Abstract

Hole transfer material (HTM)‐free, carbon‐based all‐inorganic perovskite solar cells (C‐PSCs) are promising alternatives to conventional organic–inorganic hybrid PSCs in addressing thermal and moisture instability issues. However, the energy level mismatch between the inorganic perovskite and carbon electrode coupled, together with the incapability of the carbon electrode to reflect incident light for reabsorption, limits the power conversion efficiency (PCE) of C‐PSCs. To address these issues, herein, a new strategy of a hexyltrimethylammonium bromide (HTAB)‐modified CsPbI₂Br perovskite surface is devised to reduce this energy offset from 0.70 to 0.32 eV and increase the built‐in potential by 70 mV for the final devices. Additionally, a CsPbI₂Br perovskite film with a thickness of up to 800 nm is realized via a hot‐flow‐assisted spin coating approach in an ambient atmosphere with humidity of less than 80%. Reduced energy offset coupled with suppressed charge recombination and thick perovskite layer boosts the champion PCE of CsPbI₂Br C‐PSCs to 14.3% (J _sc = 14.1 mA cm⁻², V _oc = 1.26 V, and fill factor = 0.806), and the average PCE to 13.9% under one sun illumination. A new certified efficiency record of 14.0% is obtained for HTM‐free inorganic C‐PSCs. Meanwhile, the moisture‐resistant barrier from the alkyl chain in HTAB improves the stability of the final devices.

A simple, solution-processed, highly transparent, and cost-effective polyelectrolyte hole transport layer (HTL) consisting of copper (II) poly(styrene sulfonate) (Cu:PSS) is introduced and employed in inverted perovskite solar cells. Easily reduced Cu²⁺ counter-ions balance the negative charges on the PSS polyelectrolyte backbone, supporting p-doping at the interface with the perovskite and Cu:PSS and allowing efficient extraction of p-type carriers at the anode.

Abstract

One effective strategy to improve the performance of perovskite solar cells (PSCs) is to develop new hole transport layers (HTLs). In this work, a simple polyelectrolyte HTL, copper (II) poly(styrene sulfonate) (Cu:PSS), which comprises easily reduced Cu²⁺ counter-ions with an anionic PSS polyelectrolyte backbone is investigated. Photoelectron spectroscopy reveals an increase in the work function of the anode and upward band bending effect upon incorporation of Cu:PSS in PSC devices. Cu:PSS shows a synergistic effect when mixed with polyethylenedioxythiophene: polystyrenesulfonate (PEDOT:PSS) in various proportions and results in a decrease in the acidity of PEDOT:PSS as well as reduced hysteresis in completed devices. Cu:PSS functions effectively as a HTL in PSCs, with device parameters comparable to PEDOT:PSS, while mixtures of Cu:PSS with PEDOT:PSS shows greatly improved performance compared to PEDOT:PSS alone. Optimized devices incorporating Cu:PSS/PEDOT:PSS mixtures show an improvement in efficiency from 14.35 to 19.44% using a simple CH₃NH₃PbI₃ active layer in an inverted (P-I-N) geometry, which is one of the highest values yet reported for this type of device. It is expected that this type of HTL can be employed to create p-type contacts and improve performance in other types of semiconducting devices as well.

The syntheses tactics and structural modifications of semiconducting polymers based on isoinidgo and its derivatives are comprehensively presented. The current progress of these polymers in organic field-effect transistors, chemical sensors, organic electrochemical transistors, organic phototransistors, organic photovoltaics, organic thermoelectrics, organic spin valves, and biophotonic applications is summarized, and the influences of structural modifications on device performance are discussed.

Abstract

The past few decades have witnessed the tremendous development of semiconducting polymers in electronic applications, which is inextricably related to the diversity of polymer structure. The change of polymer structure significantly influences the polymer packing, thin film morphology, and other optoelectronic properties, thus meeting the need for different device applications. With the development of synthetic chemistry and theoretical computation, many high-performance building blocks and polymers have emerged. Among them, isoindigo- and isoindigo derivatives-based polymers are widely studied in various fields of organic electronics, and many of them showed excellent properties. This review summarizes the synthetic tactics of isoindigo-derived monomers and polymers. Moreover, the structural modification strategies of polymers are discussed in detail, including the modification of isoindigo derivatives and the regulation of polymer type. Using isoindigo-derived polymers, various applications, such as organic field-effect transistors, chemical sensors, organic electrochemical transistors, organic phototransistors, organic photovoltaics, organic thermoelectrics, organic spin valves, and biophotonic applications, are introduced to illustrate the important effects of structural modification.

A facile strategy of employing an acceptor‐analogue is developed to efficiently reduce trap density to a magnitude of 10¹⁵ cm⁻³ for organic photovoltaic materials, which is comparable to and even lower than those of some inorganic counterparts, and boosts the power conversion efficiency of organic solar cells up to 17.8%.

Abstract

Typical organic semiconductor materials exhibit a high trap density of states, ranging from 10¹⁶ to 10¹⁸ cm⁻³, which is one of the important factors in limiting the improvement of power conversion efficiencies (PCEs) of organic solar cells (OSCs). In order to reduce the trap density within OSCs, a new strategy to design and synthesize an electron acceptor analogue, BTPR, is developed, which is introduced into OSCs as a third component to enhance the molecular packing order of electron acceptor with and without blending a polymer donor. Finally, the as‐cast ternary OSC devices employing BTPR show a notable PCE of 17.8%, with a low trap density (10¹⁵ cm⁻³) and a low energy loss (0.217 eV) caused by non‐radiative recombination. This PCE is among the highest values for single‐junction OSCs. The trap density of OSCs with the BTPR additives, as low as 10¹⁵ cm⁻³, is comparable to and even lower than those of several typical high‐performance inorganic/hybrid counterparts, like 10¹⁶ cm⁻³ for amorphous silicon, 10¹⁶ cm⁻³ for metal oxides, and 10¹⁴ to 10¹⁵ cm⁻³ for halide perovskite thin film, and makes it promising for OSCs to obtain a PCE of up to 20%.

Notable developments of SnO₂ as an electron‐selective layer for efficient perovskite solar cells (PSCs) are reviewed, along with an overview of the fabrication methods and interfacial passivation routes. Furthermore, techno‐economic and toxicology analyses of SnO₂ are discussed for possible large‐scale deployment of PSCs. Finally, the role of SnO₂ in scaled module and tandem solar cell production is revealed.

Abstract

Perovskite solar cells (PSCs) have become a promising photovoltaic (PV) technology, where the evolution of the electron‐selective layers (ESLs), an integral part of any PV device, has played a distinctive role to their progress. To date, the mesoporous titanium dioxide (TiO₂)/compact TiO₂ stack has been among the most used ESLs in state‐of‐the‐art PSCs. However, this material requires high‐temperature sintering and may induce hysteresis under operational conditions, raising concerns about its use toward commercialization. Recently, tin oxide (SnO₂) has emerged as an attractive alternative ESL, thanks to its wide bandgap, high optical transmission, high carrier mobility, suitable band alignment with perovskites, and decent chemical stability. Additionally, its low‐temperature processability enables compatibility with temperature‐sensitive substrates, and thus flexible devices and tandem solar cells. Here, the notable developments of SnO₂ as a perovskite‐relevant ESL are reviewed with emphasis placed on the various fabrication methods and interfacial passivation routes toward champion solar cells with high stability. Further, a techno‐economic analysis of SnO₂ materials for large‐scale deployment, together with a processing‐toxicology assessment, is presented. Finally, a perspective on how SnO₂ materials can be instrumental in successful large‐scale module and perovskite‐based tandem solar cell manufacturing is provided.

A moiré interference structure augments light‐diffraction channels, leading to elongated optical paths, and “folds” sunlight into the perovskite layer. Besides, the sets of moiré diffracted light achieve “1 + 1 = 3” comparing to the single diffraction grating. Therefore, moiré perovskite solar cells are constructed by way of a commercial DVD disc, resulting in a champion efficiency up to 20.17% (MAPbI₃) and 21.76% ((FAPbI₃)_{1‐ x} (MAPbBr₃) _x ).

Abstract

Light harvesting is crucial for thin‐film solar cells. To substantially reduce optical loss in perovskite solar cells (PSCs), hierarchical light‐trapping nano‐architectures enable absorption enhancement to exceed the conventional upper limit and have great potential for achieving state‐of‐the art optoelectronic performances. However, it remains a great challenge to design and fabricate a superior hierarchical light‐trapping nano‐architecture, which exhibits extraordinary light‐harvesting ability and simultaneously avoids deteriorating the electrical performance of PSCs. Herein, colorful efficient moiré‐PSCs are designed and fabricated incorporating moiré interference structures by the imprinting method with the aid of a commercial DVD disc. It is experimentally and theoretically demonstrated that the light harvesting ability of the moiré interference structure can be well manipulated through changing the rotation angle (0°–90°). The boosted short‐circuit current is credited to augment light diffraction channels, leading to elongated optical paths, and fold sunlight into the perovskite layer. Moreover, the imprinting process suppresses the trap sites and voids at the active‐layer interfaces with eliminated hysteresis. The moiré‐PSC with an optimized 30° rotation angle achieves the best enhancement of light harvesting (28.5% higher than the pristine), resulting in efficiencies over 20.17% (MAPbI₃) and 21.76% ((FAPbI₃)_{1‐ x} (MAPbBr₃) _x ).