awn

Herein, a self-formed multifunctional grain boundary (GB) passivation strategy is reported, where an ultrathin GB passivation layer is in situ constructed via incorporating K₂SO₄ into perovskite precursor solution. The efficiency is increased from 20.4% to 22.4% after K₂SO₄ modification along with improved stability.

The deep-level defects at grain boundary (GB) result in serious trap-assisted non-radiative recombination. Moreover, the degradation of perovskite films is preferentially triggered by the attack of GBs by water and/or oxygen. Therefore, it is urgently needed to develop a multifunctional GB tailoring strategy to address the abovementioned issues. Herein, a self-formed multifunctional GB passivation strategy is reported, where an ultrathin GB passivation layer is in situ constructed via incorporating K₂SO₄ into perovskite precursor solution. The self-formed GB passivation layer plays multiple functions, including crystallization improvement, defect passivation, and moisture resistance. The GB manipulation strategy endows perovskite films reduced defect density, boosted carrier lifetime, and thus suppressed non-radiative recombination, which contributes to efficiency enhancement from 20.39% to 22.40%. The GB tailoring approach makes the unencapsulated target device exhibit no degradation while the control device degrades to 93% of its initial power conversion efficiency after 1200 h ambient exposure with a relative humidity of 10–20%. The modified device maintains 98% of its original efficiency after aging at 60 °C for 1200 h, whereas only 89% for the control device. Herein, the importance of developing an in situ GB modification strategy in enhancing performance of perovskite photovoltaics is highlighted.

Heating colloidal tin oxide solutions changes the particle size distribution from bimodal to unimodal. This mitigates agglomerates, resulting in uniform, compact, and gap-free SnO₂ electron transport layers. Processing perovskite layers on top results in films with reduced grain boundaries and fewer defects, along with improved perovskite/SnO₂ interfaces. This facile process results in significantly enhanced perovskite solar cell performance.

Tin dioxide is a frequently reported electron transporting material for perovskite solar cells (PSCs) that yields high-performance devices and can be solution processed from aqueous colloidal solutions. While being very simple to process, electron transport layers deposited in this manner often lead to nonuniform film morphology, significantly affecting the morphology of the subsequent perovskite layer, lowering the overall device performance. Herein, it is shown that heating the SnO₂ colloidal solution (70 °C) results in compact SnO₂ films with increased surface coverage and fewer gaps in the SnO₂ film. Such films possess threefold higher lateral electrical conductivity than those obtained from room-temperature solutions. The narrow gaps in the SnO₂ film also reduce the chances of direct contact between the indium tin oxide electrode and the perovskite layer, yielding better contact with less voltage loss. The improved SnO₂ surface coverage induces larger perovskite grains (≈565 nm) than those prepared from the room-temperature solution (≈273 nm). Finally, using these compact SnO₂ layers, efficient and stable PSCs that retain ≈85% of the initial power conversion efficiency of 20.67% after 100 h of maximum power point tracking are demonstrated.

Novel Ullazine derivatives bearing thiophene units along with various functional group are reported, and their use as hole-transporting materials (HTMs) in perovskite solar cells (PSCs) is investigated. The high potential of Ullazine-based HTMs for the fabrication of efficient and stable PSCs is substantiated for the first time.

Organic hole-transporting materials (HTMs) based on the Ullazine core yield so far only moderate power conversion efficiencies of up to 13.08% in perovskite solar cells (PSCs). Aiming to fabricate efficient and stable PSCs, novel Ullazine derivatives bearing thiophene units were designed and synthesized, allowing modulation of the electronic states of the HTMs and further providing defect passivation of the perovskite surface. Experimental and theoretical analysis show that thiophene units with -N(p-MeOC₆H₄)₂ groups improve the conductivity of Ullazine HTMs, boosting the efficiency of PSCs to 20.21%. This value is the highest reported to date for Ullazine-based HTMs, and is close to the performance of Spiro-OMeTAD. In addition, unencapsulated PSCs based on the champion Ullazine exhibit superior stability with respect to Spiro-OMeTAD, retaining nearly 90% of the initial efficiency following 1000 h aging, which is ascribed to a combination of higher water repellency and passivation of defects on the perovskite surface. This work demonstrates the high potential of HTMs based on Ullazine core as substitutes to Spiro-OMeTAD.

The results of the modeling study are summarized in the figure. The figure shows the performance parameters of the solar cell device configurations containing a single perovskite CsSn_0.5Ge_0.5I₃, a double perovskite Cs₄CuSb₂Cl₁₂, and a ternary perovskite Cs₃Bi₂I₉ as light-capturing layers, respectively, after the optimization of various input parameters of the absorber layer and the device operating conditions.

A comprehensive device performance optimization of perovskite solar cells (PSCs) having the device configurations FTO/IGZO/CsSn_0.5Ge_0.5I₃/CuO/Au, FTO/IGZO/Cs₄CuSb₂Cl₁₂/CuO/Au, and FTO/IGZO/Cs₃Bi₂I₉/CuO/Au containing the single, double, and ternary perovskites CsSn_0.5Ge_0.5I₃, Cs₄CuSb₂Cl₁₂, and Cs₃Bi₂I₉, respectively, is done utilizing the SCAPS 1D tool. The bandgap tuning of the perovskite layers and the work function optimization of the rear-contact metals for the chosen device designs provide an enhanced power conversion efficiency of 23.15%, 17.39%, and 9.75% for the solar cell architecture with the light-captivating layers CsSn_0.5Ge_0.5I₃, Cs₄CuSb₂Cl₁₂, and Cs₃Bi₂I₉, respectively. Herein, it is identified the variation of electron affinity of the perovskite layer for the aforementioned device configurations does not produce any significant enhancement in the output parameters of the simulated configurations.

Herein, two spirobifluorene-based dyes are deposited from aqueous solutions as efficient anode interlayers (AILs) as a step towards all-solution-processed environmentally friendly organic solar cells. The nonacidic nature of these water-soluble small molecules solves the electrode corrosion issue associated with the commonly employed poly(3,4-ethylenedioxythiophene):poly(styrenesulfonate) (PEDOT:PSS) interlayers while producing higher efficiencies than the photovoltaic devices prepared with PEDOT:PSS AILs.

Solution-processed inverted organic solar cells (OSCs) generally use poly(3,4-ethylenedioxythiophene):poly(styrenesulfonate (PEDOT:PSS) as hole selective anode interlayer (AIL). However, the acidic nature of PEDOT:PSS considerably accelerates the degradation dynamics of OSCs, which shortens the durability of these low-cost photovoltaic devices. Small organic molecules are attracting growing interest as alternative AIL materials, but their solubility limited to toxic organic solvents hinders the production of environmentally friendly OSCs. Herein, the first inverted OSCs employing non-PEDOT:PSS solution-processed top small organic molecule AILs deposited from aqueous solution are reported. The investigated water-soluble spirobifluorene (SBF) derivatives 1 and 2 show hole mobility (≈4 × 10⁻³ cm² V⁻¹ S⁻¹) higher than PEDOT:PSS. Because of their nonacidic nature, the interlayers formed with derivatives 1 or 2 considerably delay the degradation of the top metal electrode compared to OSCs employing PEDOT:PSS interlayers. The PEDOT:PSS-free OSC devices with inverted configuration with the water-soluble SBF derivatives as AIL produce power conversion efficiencies above 5% with PTB7-Th:ITIC active layers and above 8% with PBDB-T-2Cl:Y6 active layers, respectively, with an enhancement up to 28% compared to OSCs employing PEDOT:PSS. These results correspond to the highest reported values for PEDOT:PSS-free small-molecule inverted OSCs deposited from an aqueous solution.

Herein, vacuum-deposited p–i–n perovskite solar cells employing very thin films of intrinsic organic semiconductors as the hole transport layers is studied. When no dopants nor high work function interlayers are used, the devices show a dynamic electrical behavior before reaching efficient steady state operation. Devices with small molecules are not thermally stable, as opposite to polymer transport layers in the same configuration.

Thin polymeric and small-molecular-weight organic semiconductors are widely employed as hole transport layers (HTLs) in perovskite solar cells. To ensure ohmic contact with the electrodes, the use of doping or additional high work function (WF) interlayer is common. In some cases, however, intrinsic organic semiconductors can be used without any additive or buffer layers, although their thickness must be tuned to ensure selective and ohmic hole transport. Herein, the characteristics of thin HTLs in vacuum-deposited perovskite solar cells are studied, and it is found that only very thin (<5 nm) HTLs readily result in high-performing devices, as the HTL acts as a WF enhancer while still ensuring selective hole transfer, as suggested by ultraviolet photoemission spectroscopy and Kelvin probe measurements. For thicker films (≥5 nm), a dynamic behavior for consecutive electrical measurements is observed, a phenomenon which is also common to other widely used HTLs. Finally, it is found that despite their glass transition temperature, small-molecule HTLs lead to thermally unstable solar cells, as opposed to polymeric materials. The origin of the degradation is still not clear, but might be related to chemical reactions/diffusion at the HTL/perovskite interface, in detriment of the device stability.

Structural and theoretical aspects of ABO₃ perovskites along with its photovoltaic performances aid to develop better photoanodes for dye-sensitized solar cells.

In terms of addressing the rapid global energy demand while simultaneously suppressing important environmental issues from an economic aspect, dye-sensitized solar cell (DSSC) technology has emerged as a most viable option for traditional silicon-based solar cell technology. In the DSSC, the photoanode takes precedence over other components. There have been numerous reviews of binary oxides-based photoanodes to date. From the last decade, ternary oxides, particularly ABO₃-type perovskites, have gained popularity as DSSC photoanodes. Due to their excellent physiochemical properties, supply of excellent photovoltaic performance, and simple modification method by modifying the atomic composition of their constituents, ABO₃ perovskites have firmly established themselves as innovative over the conventional photoanode materials for DSSC. The lack of a review based on ABO₃ perovskites limits its further exploration. Furthermore, the theoretical means of a material is a prerequisite to designing efficient photoanode materials for DSSC. Taking these facts into an account, this review will focus on fundamental aspects of ABO₃ perovskite materials, theoretical insights, and their potential application as photoanode materials in DSSCs. It is anticipated that this review pool will aid in gaining in-depth knowledge about ABO₃ perovskites by utilizing their experimental, theoretical, and photovoltaic aspects for future advancement.

Publication date: March 2022

Source: Nano Energy, Volume 93

Author(s): Jiachen Xi, Yeyong Wu, Weijie Chen, Qilong Li, Jiajia Li, Yunxiu Shen, Haiyang Chen, Guiying Xu, Heyi Yang, Ziyuan Chen, Na Li, Jian Zhu, Yaowen Li, Yongfang Li

A molecularly engineered cyclobutane-based hole-transporting material synthesised using simple and green-chemistry-inspired protocols achieves an impressive efficiency of 21 % in perovskite solar cells and over 19 % in perovskite solar module with an active area of 30.24 cm².

Abstract

Hybrid lead halide perovskite solar cells (PSCs) have emerged as potential competitors to silicon-based solar cells with an unprecedented increase in power conversion efficiency (PCE), nearing the breakthrough point toward commercialization. However, for hole-transporting materials, it is generally acknowledged that complex structures often create issues such as increased costs and hazardous substances in the synthetic schemes, when translated from the laboratory to manufacture on a large scale. Here, we present cyclobutane-based hole-selective materials synthesized using simple and green-chemistry inspired protocols in order to reduce costs and adverse environmental impact. A series of novel semiconductors with molecularly engineered side arms were successfully applied in perovskite solar cells. V1366-based PSCs feature impressive efficiency of 21 %, along with long-term operational stability under atmospheric environment. Most importantly, we also fabricated perovskite solar modules exhibiting a record efficiency over 19 % with an active area of 30.24 cm².

To reveal the charge-carrier dynamics in single-component organic solar cells based on a double-cable polymer, investigations across seven orders of magnitude in time scale are demonstrated. Thermal post-treatment demonstrates a positive effect on charge generation in parallel to suppressed recombination.

Abstract

Single-component organic solar cells (SCOSCs) have witnessed great improvement during the last few years with the champion efficiency jumping from the previous 2–3% to currently 6–11% for the representative material classes. However, the photophysics in many of these materials has not been sufficiently investigated, lacking essential information regarding charge-carrier dynamics as a function of microstructure, which is highly demanded for a better understanding and potential guidance for further improvements. In this work, for the first time, the charge-carrier dynamics of a representative double-cable polymer, which achieves efficiencies of over 6% as an active layer in SCOSCs, is investigated across seven orders of magnitude in time scale, from fs–ps charge generation to ns–µs charge recombination processes. Specific emphasis is placed on understanding the impact of thermal post-treatment on the charge dissociation and recombination dynamics. Annealing the photoactive layer at 230 °C results in the highest photovoltaic performance because of efficient charge generation in parallel to suppressed recombination. This work intends to present a complete picture of the charge-carrier dynamics in SCOSCs using the representative double-cable polymer PBDBPBICl.

The authors demonstrate that designing functional fullerenes with roles beyond defect passivation is essential for perovskite solar cells (PSCs). By taking the advantages of fullerene, porphyrin, and pentafluorophenyl, a novel fullerene-porphyrin dyad is intentionally synthesized to stitch grain boundaries and trap lead ions in the perovskite film by forming chemical interactions in-situ. This robust strategy yields high-performance and eco-friendly PSCs.

Abstract

Designing functional fullerenes with roles beyond defect passivation and electron-transporting for perovskite solar cells (PSCs) is essential to the development of fullerenes and PSCs. Here, the authors design and synthesize a functional fullerene, FPD, composed of a C₆₀ cage, a porphyrin ring, and three pentafluorophenyl groups. The structure features of FPD enable it can form chemical interactions with the perovskite lattices. These interactions enhance the defect passivation effect and prevent the decomposition of perovskite under irradiation. As a result, the FPD-based device yields an improved power conversion efficiency of 23% with substantially enhanced operational stability (T ₈₀ > 1500 h). Furthermore, once got damaged, the FPD can prevent lead leakage by forming a stable and water-insoluble complex (FPD-Pb). Their findings provide a novel strategy to achieve high-performance and eco-friendly PSCs with functional fullerene materials.

Adding methylammonium bromide into the precursor solution of double perovskites promotes the high-quality crystallization of Cs₂AgBiBr₆, obtaining dense surface and less pin-holes. Reduced trap density and longer carrier lifetime are also observed. The power conversion efficiency reaches 2.53%, significantly higher than 1.43% of control device, beneficial from the efficient carrier collection with suppressed defect-assisted recombination.

Abstract

Cs₂AgBiBr₆, has recently gained wide attention as a possible alternative to lead-halide perovskites, considering the nontoxicity and improved stability. However, this double perovskite suffers from defects, especially deep electron traps, severely hampering the photovoltaic performance. This work reports a simple method to control the double perovskite crystallization by adding volatile salts into the precursor solution. X-ray diffraction patterns reveal that the organic cation with suitable radius (such as methylammonium, MA⁺) is introduced into the perovskite lattice, forming an organic/inorganic mixed double perovskite intermediate phase. The organic salt is thereafter fully evaporated during high temperature annealing, and the all-inorganic double perovskite is obtained with dense surface and less pin-holes. From optical and electrical characterization, it is concluded that the Cs₂AgBiBr₆ film exhibits high quality, with higher light absorptance and emission. Reduced trap density and longer carrier lifetime are also observed. The improved Cs₂AgBiBr₆ film is beneficial for efficient carrier collection with suppressed defect-assisted recombination. With this strategy, a power conversion efficiency (PCE) of 2.53% is achieved for the champion Cs₂AgBiBr₆-based solar cell device, which is significantly higher compared to the control device with 1.43% PCE. This work is therefore helpful for further improvement of inorganic lead-free perovskite materials for optoelectronic applications.

Roll-to-roll fabrication of perovskite solar cells (PSCs) on flexible substrates represents a promising approach for commercialization. By using a triple cation perovskite and a novel passivation strategy by doping guanidinium iodide into poly(3,4-ethylenedioxythiophene):polystyrene sulfonate, it is demonstrated that slot-die-coated PSCs under ambient environment enables millimeter-sized perovskite clusters, leading to a record power conversion efficiency of 12%.

Abstract

The high-power conversion efficiencies (PCEs) of perovskite solar cells (PSCs) on lab-scale devices trigger the need to develop scalable manufacturing processes to accelerate their commercialization transition. A roll-to-roll (R2R) vacuum-free printing on flexible substrates allows for high-volume and low-cost manufacturing which is especially well-suited for PSCs due to its solution processibility and low-temperature annealing requirements. Herein, a facile hot deposition technique is reported to fabricate triple-cation (Cs_0.07FA_0.79MA_0.14Pb(I_0.83Br_0.17)₃) perovskite films in an ambient environment using a R2R slot-die coating method. This perovskite composition, whilst being most studied in lab devices due to its high efficiency and stability, has not been applied in R2R fabrication thus far. The demonstrated R2R slot-die coated flexible PSCs achieve stabilized PCE reaching 12% at maximum power point in inverted “p-i-n” architectures, the highest efficiency reported to date for R2R inverted PSCs. To achieve this, the underlying hole transport layer (poly(3,4-ethylenedioxythiophene):polystyrene sulfonate) is modified with guanidinium iodide additive which leads to the formation of large millimeter-sized perovskite clusters, improved perovskite crystallinity, and enhanced charge-transfer efficiency. This study highlights the potential of the facile hot-deposition method while providing critical insights into the role of interfacial engineering in eliminating performance losses and fabricating efficient printed flexible PSCs.

Herein, a simple dynamic vacuum-assisted low-temperature engineering is developed to prepare high quality CsPbIBr₂ film (VALT-CsPbIBr₂ film). The derived VALT-CsPbIBr₂ PSCs yield a superior PCE of 11.01% with a remarkable fill factor of 75.31%, which both are impressive among the reported CsPbIBr₂ PSCs. Meanwhile, VALT-CsPbIBr₂ PSCs feature stronger endurance against heat and moisture than control ones.

Among all-inorganic perovskite photoactive materials, CsPbIBr₂ demonstrates the most balanced trade-off between optical bandgap and phase stability. However, the poor quality and high-temperature engineering of CsPbIBr₂ film hinder the further optimization of derived perovskite solar cells (PSCs). Herein, a simple dynamic vacuum-assisted low-temperature engineering (merely 140 °C) is proposed to prepare high-quality CsPbIBr₂ film (VALT-CsPbIBr₂ film). Compared to HT-CsPbIBr₂ film processed via conventionally high temperature (280 °C), VALT-CsPbIBr₂ film presents higher crystallinity and more full coverage consisting of larger grains and fewer grain boundaries, which results in intensified light-harvesting capability, reduced defects, and extended charge carrier lifetime. Benefiting from those improved merits, VALT-CsPbIBr₂ PSCs show lower trap-state densities, more proficient charge dynamics, and larger built-in potential than HT-CsPbIBr₂ PSCs. Consequently, VALT-CsPbIBr₂ PSCs deliver a higher efficiency of 11.01% accompanied by a large open-circuit voltage of 1.289 V and a remarkable fill factor of 75.31%, being highly impressive among those reported CsPbIBr₂ PSCs. By contrast, the efficiency of HT-CsPbIBr₂ PSCs is only 9.00%. Moreover, VALT-CsPbIBr₂ PSCs present stronger endurance against heat and moisture than HT-CsPbIBr₂ PSCs. Herein, a feasible avenue to fabricate efficient yet stable all-inorganic PSCs via low-temperature engineering is provided.

The buried ionic liquid functional layer provides electron-rich environment for the perovskite growth to suppress Sn²⁺ oxidation, resulting in improved bulk crystallinity. Consequently, a high efficiency of 11.28% is obtained for the inorganic CsPb_0.75Sn_0.25I₂Br perovskite solar cells (PSCs).

The enlightening inorganic Sn-based metal halide perovskites hold promise for environment-friendly and efficient energy conversion. However, the undesired Sn²⁺ oxidation and uncontrollable crystallization of the perovskite absorber slow the development of highly efficient Sn-based inorganic perovskite solar cells. Herein, an ionic liquid layer of 1-butylpyridinium bromide (BPB) is employed as a buried functional template for the growth of the inorganic CsPb_0.75Sn_0.25I₂Br perovskite absorber. The buried functional layer provides lone electron pairs from N atom to coordinate with the unsaturated metal ions (Pb and Sn) via the coupling effect. In addition, the electronegative atom from the hydrogen bond acceptor offers an electron-rich environment for the perovskite growth to suppress Sn²⁺ oxidation. More importantly, this positive effect transduces from the interface to the bulk perovskite growth, leading to enhanced crystallinity and thus reduced nonradiative trap defects. Consequently, the efficiency of the inorganic CsPb_0.75Sn_0.25I₂Br PSCs is improved from 6.80% to 11.28%, and the unencapsulated device exhibits superior ambient stability, maintaining 62% of its initial power conversion efficiency in dried air for 200 h. The buried ionic liquid functional layer approach provides an avenue for the development of high-efficiency Sn-based optoelectronics.

A new D–π–A-type Zinc zinc pyridine porphyrin derivative (ZnPP) is synthesized and used as a graded passivation molecular for modifying the perovskite solar cell (PSC). It is found that ZnPP treatment significantly improves the quality of perovskite films and passivates the defects, yielding devices with a high efficiency of 21.08% with fill factor (FF) of 82.91

While perovskite solar cells (PSCs) have recently experienced a rapid rise in power conversion efficiency (PCE), the prevailing PSCs still contain nondesirable defects in the interior and interface of the perovskite layer, which limits further enhancement in PCE and device stability. Herein, a new D–π–A-type zinc pyridine porphyrin derivative (ZnPP) is synthesized and used as a passivation molecular via the antisolvent process for modifying the typical perovskite bulk thin film, leading to a new type of PSC with a graded passivation of the perovskite layer. Impressively, it is found that ZnPP treatment significantly improves the quality of perovskite films and reduces charge transport losses through passivating the uncoordinated Pb²⁺ cations, yielding devices with a high efficiency of 21.08% with fill factor (FF) of 82.91% and demonstrating the promise of integration of perovskite bulk thin films with tailor molecular via graded modification.

In this work, highly foldable polyimide (PI)/silver nanowires (AgNWs) conductive substrates with 1000 cyclic mechanical stability are constructed by embedding AgNWs into ultrathin PI films. The perovskite solar cells on PI/AgNWs exhibit high folding stability which can endure bending at a curvature radius of 0.4 mm as well as direct folding for 1000 cycles.

Abstract

Foldable solar cells, with the advantages of size compactness and shape transformation, are attractive power sources for wearable and portable devices. The challenge for realizing highly foldable solar cells is to exploit highly foldable conductive substrates to replace brittle indium tin oxide. In this work, highly foldable and smooth polyimide (PI)/silver nanowires (AgNWs) conductive substrates are constructed by embedding AgNWs into ultrathin PI films to improve the interface binding force. As a result, the embedded PI/AgNWs complex shows a neglectable change in resistance after folding for 1000 cycles. The perovskite solar cells (PSCs) on PI/AgNWs substrates exhibit power conversion efficiency (PCE) of 11.8%. More importantly, beneficial from the highly foldable PI/AgNWs conductive substrates, the PSCs maintain 73.5% and 55.2% of the initial PCE after +180° and −180° folding for 1000 cycles, respectively, which is the first report on the foldable AgNWs-based PSCs. In addition, the degradation mechanism of PSCs subjected to different folding conditions is tentatively exploited. This work paves the way toward realizing highly foldable PSCs for various practical applications.

MXene sheets are inserted between silver nanowires and graphene to fill the voids of the network and connect the nanowires with graphene. The nanowire junctions are welded together due to the solvent evaporation effect and thermal effect. The proposed transparent conductive electrodes show good photoelectric performance, stability under various environmental conditions, and are used to prepare organic solar cells.

Abstract

Flexible transparent conductive electrodes (TCEs) are an essential part of flexible electronic and energy devices. As a promising alternative to ITO (In₂O₃:Sn), silver nanowire has poor environmental stability and adhesion, which limits its development. Herein, transition metal carbides and carbonitrides called MXene are inserted between silver nanowires and graphene grown by chemical vapor deposition to improve the conductivity, adhesion, roughness, and stability of the electrode. Nanosheets fill the voids of the network and connect the nanowires with graphene to provide more conductive channels. In addition, due to the solvent evaporation effect and thermal effect in the preparation process, the nanowire junctions are welded together. Based on the unique structure, the proposed composite TCE shows low sheet resistance (18.1 Ω sq⁻¹) and high optical transmittance (88.1% at 550 nm). Furthermore, compared to the reference samples, the composite TCEs demonstrate stable electrical performances under different environmental conditions, including thermal environment, exposures to air for 80 days, and bending for 2000 cycles. Finally, flexible organic solar cells (OSCs) are prepared using the composite TCEs, which show comparable efficiency to that of ITO-based OSCs. Therefore, the flexible transparent electrodes are expected to be applied in solar cells, organic light-emitting diodes, and a broader range.

Nanoepitaxy growth of Sb₂Se₃ nanorod arrays (NRAs) is carried out on polycrystalline, randomly orientated fluorine-doped tin oxide-coated glass substrates for efficient and quasiomnidirectional solar cells. The thermodynamic and kinetic processes behind the growth of Sb₂Se₃ NRAs on polycrystalline surfaces are discussed. The broadband quasiomnidirectional characteristics of Sb₂Se₃ NRA solar cells are investigated and found to be favorable with respect to planar devices.

Low-symmetric and structurally anisotropic materials are of widespread research interest. Antimony selenide and analogues from group V₂−VI₃ metal chalcogenides, have emerged recently due to their distinctive crystalline symmetries, highly anisotropic electronic and physical properties, Earth abundance, and environmentally friendly characteristics. Its intrinsic quasi-1D crystal structure leads to much easier and efficient carrier transport along the [hk1] orientation than in other directions. Effective manipulation of the growth orientation and concomitant natural features of the anisotropic materials, which are crucial for the device performance based on the anisotropic Sb₂Se₃, is still poorly developed. Herein, the growth of monocrystalline Sb₂Se₃ nanorod arrays (NRAs) along the [hk1] orientation on polycrystalline and mixed-oriented fluorine-doped tin oxide (SnO₂:F, FTO) glass is carried out under different growth conditions. The thermodynamic and kinetic processes behind the growth of Sb₂Se₃ NRAs on polycrystalline surfaces are discussed. Solar cells based on the [hk1]-oriented Sb₂Se₃ NRAs achieve a power conversion efficiency of 9.0%, comparable with the conversion efficiency of the state-of-the-art Sb₂Se₃ solar cells. Moreover, these Sb₂Se₃ NRA solar cells exhibit quasiomnidirectional light absorption characteristics, showing high potential as solar cells with high output power over extended daytime operating hours.

Polyacrylonitrile which has C≡N groups was introduced to passivate the uncoordinated lead cations in perovskite films. The coordination of C≡N with the lead cation was much stronger than that of the normally used C=O group. It could also reduce the I/Pb ratio at the film surface. The device efficiency was improved from 21.58 % to 23.71 %, with the open-circuit voltage enhanced from 1.12 V to 1.23 V.

Abstract

In solution-processed organic–inorganic halide perovskite films, halide-anion related defects including halide vacancies and interstitial defects can easily form at the surfaces and grain boundaries. The uncoordinated lead cations produce defect levels within the band gap, and the excess iodides disturb the interfacial carrier transport. Thus these defects lead to severe nonradiative recombination, hysteresis, and large energy loss in the device. Herein, polyacrylonitrile (PAN) was introduced to passivate the uncoordinated lead cations in the perovskite films. The coordinating ability of cyano group was found to be stronger than that of the normally used carbonyl groups, and the strong coordination could reduce the I/Pb ratio at the film surface. With the PAN perovskite film, the device efficiency improved from 21.58 % to 23.71 % and the open-circuit voltage from 1.12 V to 1.23 V, the ion migration activation energy increased, and operational stability improved.

Two small-molecule donors, SM-BF1 and SM-BF2, are synthesized by a low-cost synthesis route utilizing cheap raw materials. The champion device based on SM-BF1:Y6 shows a power conversion efficiency (PCE) of 15.71%, benefitted from its better miscible morphology and more balanced charge-carrier transport characteristics. Furthermore, through the figure of merit (FOM) analysis, SM-BF1 also shows a good prospect for commercial application.

Abstract

Low cost, high efficiency, and high stability are the three key issues of organic solar cells (OSCs) that should be carefully considered to meet the requirement of future commercial applications. Therefore, the development of high-performance organic photovoltaic materials with low synthetic cost has been becoming a crucial challenge in the field of OSCs. Herein, two new low-cost small-molecule donors (SM-BF1 and SM-BF2) are designed and synthesized with a facile synthetic route by replacing 4-bromo-2-fluorobenzenethiol and 4-bromo-3-fluorobenzenethiol with low-cost 4-bromo-2-fluoro-1-iodobenzene and 4-bromo-3-fluoro-1-iodobenzene as key raw materials. Besides, the influence of the chemical steric effect of the phenyl conjugated side chains of the benzodithiophene (BDT) unit on photophysical properties, charge transfer, and photovoltaic properties are deeply investigated by the modulation of fluorine atom substituted position. As a result, SM-BF1 with ortho-fluorinated substituent has outstanding crystallization properties and better miscibility with acceptor Y6 and exhibits more desirable morphology and more balanced charge-carrier transport properties, leading to a superior power conversion efficiency (PCE) to 15.71%. More encouragingly, according to the figure of merit (FOM) and the industrial figure of merit (i-FOM) to evaluate the small-molecule donors, the SM-BF1-based device has excellent potential for future commercial applications.

By taking advantage of the synergetic effect of diradical feature and strong intermolecular interactions, a stable croconium derivative, CR-DPA-T, with high-spin state and ultra-broadband absorption covering 300 to 2000 nm in the aggregated state is obtained. CR-DPA-T demonstrates highly efficient photothermal conversion promoted by multiple nonradiative decay pathways, being a potential candidate for solar thermoelectric generation.

Abstract

Organic materials with radical characteristics are gaining increasing attention, due to their potential implications in highly efficient utilization of solar energy. Manipulating intermolecular interactions is crucial for tuning radical properties, as well as regulating their absorption bands, and thus improving the photothermal conversion efficiency. Herein, a diradical-featured organic small-molecule croconium derivative, CR-DPA-T, is reported for highly efficient utilization of solar energy. Upon aggregation, CR-DPA-T exists in dimer form, stabilized by the strong intermolecular π–π interactions, and exhibits a rarely reported high-spin state. Benefiting from the synergic effects of radical characteristics and strong intermolecular π–π interactions, CR-DPA-T powder absorbs broadly from 300 to 2000 nm. In-depth investigations with transient absorption analysis reveal that the strong intermolecular π–π interactions can promote nonradiative relaxation by accelerating internal conversion and facilitating intermolecular charge transfer (ICT) between dimeric molecules to open up faster internal conversion pathways. Remarkably, CR-DPA-T powder demonstrates a high photothermal efficiency of 79.5% under 808 nm laser irradiation. By employing CR-DPA-T as a solar harvester, a CR-DPA-T-loaded flexible self-healing poly(dimethylsiloxane) (H-PDMS) film, named as H-PDMS/CR-DPA-T self-healing film, is fabricated and employed for solar–thermal applications. These findings provide a feasible guideline for developing highly efficient diradical-featured organic photothermal materials.

An aerosol-assisted crystallization method to prepare high-quality, pure α-FAPbI₃ films at only 100 °C without chemical additives is reported. Remarkably improved phase stability of the α-FAPbI₃ films and their applications in solar cells are demonstrated. The overriding mechanism of stabilizing α-FAPbI₃ is shown to be relaxation of residual tensile strains in the films.

Abstract

Formamidinium lead triiodide (FAPbI₃) is attractive for photovoltaic devices due to its optimal bandgap at around 1.45 eV and improved thermal stability compared with methylammonium-based perovskites. Crystallization of phase-pure α-FAPbI₃ conventionally requires high-temperature thermal annealing at 150 °C whilst the obtained α-FAPbI₃ is metastable at room temperature. Here, aerosol-assisted crystallization (AAC) is reported, which converts yellow δ-FAPbI₃ into black α-FAPbI₃ at only 100 °C using precursor solutions containing only lead iodide and formamidinium iodide with no chemical additives. The obtained α-FAPbI₃ exhibits remarkably enhanced stability compared to the 150 °C annealed counterparts, in combination with improvements in film crystallinity and photoluminescence yield. Using X-ray diffraction, X-ray scattering, and density functional theory simulation, it is identified that relaxation of residual tensile strains, achieved through the lower annealing temperature and post-crystallization crystal growth during AAC, is the key factor that facilitates the formation of phase-stable α-FAPbI₃. This overcomes the strain-induced lattice expansion that is known to cause the metastability of α-FAPbI₃. Accordingly, pure FAPbI₃ p–i–n solar cells are reported, facilitated by the low-temperature (≤100 °C) AAC processing, which demonstrates increases of both power conversion efficiency and operational stability compared to devices fabricated using 150 °C annealed films.