Chen Weijie

Nature Photonics, Published online: 10 April 2023; doi:10.1038/s41566-023-01180-6

Herein, a two-step vapor–solid reaction approach is developed to deposit high-quality methylamine-free hybrid perovskite thin films with large grain size exceeding 1.5 μm. Perovskite solar cells based on these thin films have achieved a remarkable champion power conversion efficiency of 20.79%.

Thin-film solar cells based on organic–inorganic hybrid perovskite light absorbers have attracted intense attention both from the scientific and industrial communities in recent years. Researchers worldwide have developed various strategies for depositing high-quality perovskite thin films including composition optimization, surface modification, and solvent engineering. However, these strategies are mainly based on the perovskite thin films which are deposited via solution processes. Though vacuum and vapor-based techniques have been widely used in the modern thin-film industry, these technologies still need further developments for the deposition of high-quality organic–inorganic hybrid perovskite thin films. Herein, a novel two-step vapor–solid reaction procedure for the deposition of high-quality methylamine-free hybrid perovskite thin films is proposed. The first vapor–solid reaction step gives the perovskite a proper chemical stoichiometric ratio, and the second step can refine the crystallinity of the film. Therefore, by utilizing this method, it is possible to obtain high-quality perovskite thin films with larger grain sizes and lower tap densities. Consequently, perovskite solar cells based on these films have achieved a high power conversion efficiency of 20.79%.

A good compatibility between fullerene PC₇₀BM or nonfullerene ITIC-M as guest and Y7 as host acceptors with higher lowest unoccupied molecular orbital energy level to achieve complementary absorption is the key to realizing synergistically modified nanomorphology and photophysical processes toward 17.7% efficiency of PM6:Y7-based ternary organic solar cells, higher than those of 16.46% in binary device.

A ternary strategy has been demonstrated as being an effective method to improve the power conversion efficiency (PCE); however, general rules for materials selection are not fully comprehended. Herein, nonfullerene acceptor ITIC-M and fullerene acceptor PC₇₀BM possessing higher lowest unoccupied molecular orbital (LUMO) and good miscibility with nonfullerene acceptor Y7 are incorporated as third components in the state-of-the-art of PM6:Y7 binary blend. As a result, the device PCE for both ternary devices improves from 16.46% for binary host to 17.73% and 17.67% for ITIC-M- and PC₇₀BM-based ternary devices, respectively. The higher LUMO of the guest acceptor can play multiple roles to elevate the open-circuit voltage such as reducing energy-loss and reverse saturation current, creating less-localized shallow trap sites along with suppressing charge recombination, and decreasing Urbach energy. Moreover, the good miscibility facilitates an alloy-like phase in acceptors domain for efficient exciton dissociation and electron transport, which leads to improved short-circuit current density and fill factor in ternary devices. The results provide a promising approach to realize high-performance ternary organic solar cells by synergizing the compatible third component with host acceptor.

Star-shaped unfused ring electron acceptors are incorporated, for the first time, as third components into binary bulk heterojunction to drastically enhance organic solar cell performance. The concept of structural complementarity is proposed for ternary bulk heterojunction organic solar cells, that is, star-shaped unfused ring acceptors incorporated into linear donor and linear fused ring-based acceptor blends.

Ternary strategy has attracted extensive attention for bulk heterojunction organic solar cells (BHJ OSCs) owing to their potentially improved light harvesting, cascaded energy levels, and optimized film morphology of binary BHJs. Herein, three novel star-shaped unfused ring electron acceptors (SSUFREAs), i.e., H1–3, with and without fluorine-substituent in phenyl core or peripheral group are designed and synthesized as third components via direct C–H arylation to incorporate into PM6:Y6 BHJ films. The structure–property–performance dependence study reveals that the isotropic charge transfer, complementary star-shape structure and light absorption, and energy-level cascades of H1–3 with PM6 and Y6 allow ternary BHJs to have higher power conversion efficiency (PCE) compared to the PM6:Y6 binary BHJ. Among them, the ternary BHJ involving fluorine-free H1, i.e., H1:PM6:Y6, possesses the highest PCE (16.57%) owing to the high-lying frontier molecular orbital and the enlarged torsion angle, which enhances open-circuit voltage, inhibits the excessive crystallization of Y6, and facilitates exciton dissociation as well as collection. The findings indicate that SSUFREAs have great potential to serve as third components to optimize morphology and improve the open-circuit voltage of BHJ OSCs.

PM6:Y6:PC₇₁BM ternary organic solar cells are prepared with 1,8-diiodooctane (DIO) and 1-chloronaphthalene (CN) binary additives. The addition of trace amounts of the second additive (DIO) further improves the molecule packing of active layer and induces acceptor materials on the active layer surface. An improved power conversion efficiency of 17.53% is achieved.

Solvent additive can be used to regulate active layer morphology and improve photovoltaic performance of organic solar cells (OSCs). Herein, the PM6:Y6:PC₇₁BM ternary bulk heterojunction OSCs are prepared by introducing 1,8-diiodooctane (DIO) and 1-chloronaphthalene (CN) as binary additives. On the basis of optimizing the photovoltaic performance with CN additive, the addition of trace amounts of DIO additive further improves the molecular packing of active layer and induces Y6:PC₇₁BM acceptor on the surface of active layer. With the optimized active layer morphology, the CN and DIO binary additives restrict carrier recombination and improve charge transport efficiently, and the prepared PM6:Y6:PC₇₁BM ternary OSCs with binary additives demonstrate a high short-circuit current density of 27.15 mA cm⁻² and a fill factor of 76.79%, and yield an improved power conversion efficiency of 17.53%, which is higher than that of devices without additives (16.50%) and with DIO (16.79%) or CN additive (17.21%). Binary solvent additives engineering provides an effective strategy to finely regulate active morphology and boost photovoltaic performance of ternary OSCs.

By the passivation of 12-aminolauric acid, the efficiency of the perovskite solar cells (PSCs) can increase from 18.42% to 19.96%. The treatments of the passivation agents also increase the hydrophobicity of the perovskite films, improving the stability of the PSCs.

Defects in perovskite film are sources of charge recombination centers, which are detrimental to the performance of perovskite solar cells (PSCs). To decrease the density of defects, dodecylamine (DAM), dodecylic acid (DAC), and 12-aminolauric acid (ALA) are utilized as additives to prepare methyl ammonium lead iodide (MAPbI₃) perovskite films. Herein, the passivation effects of these molecules on the properties of the MAPbI₃ films and the performances of the corresponding PSCs are studied. The results show that DAM and DAC which contain –NH₂ and –COOH groups, respectively, can increase the PCEs of the devices. This result implies that both groups serve as the Lewis base, passivating the defects of undercoordinated Pb²⁺. For the ALA molecules, the –NH₂ and –COOH groups are present simultaneously at the two ends of the molecule; the passivation ability is more significant than the others, which is attributable to the synergistic effects of the two groups. By the passivation of ALA, the PCE of the PSC can increase from 18.42% to 19.96% under one sun illumination. Furthermore, the treatments of the passivation agents also increase the hydrophobicity of the perovskite films, improving the stability of the PSCs.

By incorporating bottom decoration in perovskite film, the Piperazine Dihydriodide (PDI₂) layer can alleviate the mismatched thermal expansion between the perovskite and substrate. This enables the PDI₂ layer to function as a lubricant, resulting in the release of lattice strain and the formation of a void-free buried interface. The modulation leads to a significant enhancement in performance of solar cells.

Abstract

Given that it is closely related to perovskite crystallization and interfacial trap densities, buried interfacial engineering is crucial for creating effective and stable perovskite solar cells. Compared with the in-depth studies on the defect at the top perovskite interface, exploring the defect of the buried side of perovskite film is relatively complicated and scanty owing to the non-exposed feature. Herein, the degradation process is probed from the buried side of perovskite films with continuous illumination and its effects on morphology and photoelectronic characteristics with a facile lift-off method. Additionally, a buffer layer of Piperazine Dihydriodide (PDI₂) is inserted into the imbedded bottom interface. The PDI₂ buffer layer is able to lubricate the mismatched thermal expansion between perovskite and substrate, resulting in the release of lattice strain and thus a void-free buried interface. With the PDI₂ buffer layer, the degradation originates from the growing voids and increasing non-radiative recombination at the imbedded bottom interfaces are suppressed effectively, leading to prolonged operation lifetime of the perovskite solar cells. As a result, the power conversion efficiency of an optimized p-i-n inverted photovoltaic device reaches 23.47% (with certified 23.42%) and the unencapsulated devices maintain 90.27% of initial efficiency after 800 h continuous light soaking.

A BF₄ ⁻ anion–assisted molecular doping (AMD) strategy is proposed to enhance the doping level of both poly[bis(4-phenyl) (2,4,6-trimethylphenyl) amine] and poly[N,N′-bis(4-butilphenyl)-N,N′-bis(phenyl)-benzidine] films and induce the formation of p–n homojunctions in the perovskite film, which results in a highest power conversion efficiency of 24.26% due to the reduced energy loss at the buried interface.

Abstract

The energy loss (E _loss) aroused by inefficient charge transfer and large energy level offset at the buried interface of p-i-n perovskite solar cells (PVSCs) limits their development. In this work, a BF₄ ⁻ anion-assisted molecular doping (AMD) strategy is first proposed to improve the charge transfer capability of hole transport layers (HTLs) and reduce the energy level offset at the buried interface of PVSCs. The AMD strategy improves the carrier mobility and density of poly[bis(4-phenyl) (2,4,6-trimethylphenyl) amine] (PTAA) and poly[N,N′-bis(4-butilphenyl)-N,N′-bis(phenyl)-benzidine] (Poly-TPD) HTLs while lowering their Fermi levels. Meanwhile, BF4− anions regulate the crystallization and reduce donor-type iodine vacancies, resulting in the energetics transformation from n-type to p-type on the bottom surface of perovskite film. The faster charge transfer and formed p–n homojunction reduce charge recombination and E _loss at the HTL/perovskite buried interface. The PVSCs utilizing AMD treated PTAA and Poly-TPD as HTLs demonstrate a highest power conversion efficiency (PCE) of 24.26% and 22.65%, along with retaining 90.97% and 85.95% of the initial PCE after maximum power point tracking for 400 h. This work provides an effective way to minimize the E _loss at the buried interface of p-i-n PVSCs by accelerating charge transfer and forming p–n homojunctions.

This study demonstrates a novel, highly transparent Al_yTiO_x/ZnO/TiO₂ stack, based on earth-abundant materials, that simultaneously achieves outstanding silicon surface passivation while maintaining very low contact resistivity, providing a close-to-ideal passivating contact to silicon surfaces. Device simulations reveal that the electrical characteristics of such contacts wouldnot limit the performance of c-Si solar cells, when compared to state-of-the-art SiO_x/poly-Si contacts.

Abstract

Passivating contact technologies are essential for fabricating high-efficiency crystalline silicon (c-Si) solar cells, and their application and incorporation into manufacturing lines has ranked as a hot topic of research. Generally, ideal passivating contacts should combine excellent electrical contact, outstanding surface passivation, and high optical transparency. However, addressing all these criteria concurrently is challenging since it is unlikely for any single material to exhibit both efficient carrier transport and surface-defect passivation while demonstrating negligible parasitic absorption. In this work, several earth-abundant, wide-bandgap materials are combined to engineer high-quality transparent electron-selective passivating contact structures capable of overcoming these obstacles. A highly transparent Al_yTiO_x/ZnO/TiO₂ stack with a total thickness of 3 nm, prepared by atomic layer deposition, is shown to provide a close-to-ideal passivating contact to Si surfaces by enabling dual functions of remarkable silicon surface passivation (with an effective minority carrier lifetime of 12.3 ms, an implied open-circuit voltage of 730 mV, and a surface recombination current density prefactor of 2.6 fA cm⁻²), combined with efficient carrier transport with a very low contact resistivity of 3.4 mΩ cm². These results demonstrate that low-cost silicon interface-engineering strategiesbased on transition metal oxides can push c-Si solar cell performance to its theoretical limits.

A simple, facile, and versatile strategy of pre-grafted halides is developed for strengthening the SnO₂–perovskite buried interface, in which precise manipulation of perovskite defects and carrier dynamics has been realized by altering halide electronegativity (χ).

Abstract

The perovskite buried interfaces have demonstrated pivotal roles in determining both the efficiency and stability of perovskite solar cells (PSCs); however, challenges remain in understanding and managing the interfaces due to their non-exposed feature. Here, we proposed a versatile strategy of pre-grafted halides to strengthen the SnO₂–perovskite buried interface by precisely manipulating perovskite defects and carrier dynamics through alteration of halide electronegativity (χ), thereby resulting in both favorable perovskite crystallization and minimized interfacial carrier losses. Specifically, the implementation of fluoride with the highest χ induces the strongest binding affinity to uncoordinated SnO₂ defects and perovskite cations, leading to retarded perovskite crystallization and high-quality perovskite films with reduced residual stress. These improved properties enable champion efficiencies of 24.2% (the control: 20.5%) and 22.1% (the control: 18.7%) in rigid and flexible devices with extremely low voltage deficit down to 386 mV, all of which are among the highest reported values for PSCs with a similar device architecture. In addition, the resulting devices exhibit marked improvements in the device longevity under various stressors of humidity (>5000 h), light (1000 h), heat (180 h), and bending test (10 000 times). This method provides an effective way to improve the quality of buried interfaces toward high-performance PSCs.

Through single-molecule detection, it is found that an acceptor–donor–acceptor (A–D–A)-type molecule with 1,1-dicyano methylene-3-indanone acceptor units exhibits enhanced conductance compared with the control donor molecule. Furthermore, the charge transport of the D central part is directly detected, proving that the conductive orbitals contributed by the acceptor groups can penetrate the whole A–D–A molecule.

Abstract

The electronic characteristics of organic optoelectronic materials determine the performance of corresponding devices. Clarifying the relationship between molecular structure and electronic characteristics at the single-molecule level can help to achieve high performance for organic optoelectronic materials and devices, especially for organic photovoltaics. In this work, a typical acceptor–donor–acceptor (A–D–A)-type molecule is explored by combining theoretical and experimental studies to reveal the intrinsic electronic characteristics at the single-molecule level. Specifically, the A–D–A-type molecule with 1,1-dicyano methylene-3-indanone (INCN) acceptor units exhibits an enhanced conductance in single-molecule junctions when compared with the control donor molecule, because the acceptor units of the A–D–A-type molecule contribute additional transport channels. In addition, through opening the S∙∙∙O noncovalent conformational lock by protonation to expose the −S anchoring sites, the charge transport of the D central part is detected, proving that the conductive orbitals contributed by the INCN acceptor groups can penetrate the whole A–D–A molecule. These results provide important insights into the development of high-performance organic optoelectronic materials and devices toward practical applications.

An interfacial gradient heterostructure (denoted as BTA⁺-CsPbI_3−x Br _x ) is constructed to simultaneously tune CsPbI₃ perovskite defects and interfacial energy levels. This strategy can significantly suppress nonradiative recombination in perovskites and facilitate charge transfer in a device. An efficiency of 21.31% is achieved for CsPbI₃ solar cells, and a record efficiency of 16.60% is demonstrated for printed inorganic CsPbI₃ minimodules.

Abstract

Severe nonradiative recombination originating from interfacial defects together with the pervasive energy level mismatch at the interface remarkably limits the performance of CsPbI₃ perovskite solar cells (PSCs). These issues need to be addressed urgently for high-performance cells and their applications. Herein, an interfacial gradient heterostructure based on low-temperature post-treatment of quaternary bromide salts for efficient CsPbI₃ PSCs with an impressive efficiency of 21.31% and an extraordinary fill factor of 0.854 is demonstrated. Further investigation reveals that Br⁻ ions diffuse into the perovskite films to heal undercoordinated Pb²⁺ and inhibit Pb cluster formation, thus suppressing nonradiative recombination in CsPbI₃. Meanwhile, a more compatible interfacial energy level alignment resulting from Br⁻ gradient distribution and organic cations surface termination is also achieved, hence promoting charge separation and collection. Consequently, the printed small-size cell with an efficiency of 20.28% and 12 cm² printed CsPbI₃ minimodules with a record efficiency of 16.60% are also demonstrated. Moreover, the unencapsulated CsPbI₃ films and devices exhibit superior stability.

Antisolvent engineering is proposed to realize high-quality dominantly oriented perovskite film by the antisolvent of isopropyl alcohol (IPA). The interaction between IPA and PbI₂ leads to the direct crystallization of (111)-α-FAPbI₃ at room temperature, sidestepping the intermediates of PbI₂•DMSO, FA₂Pb₃I₈•4DMSO, and δ-FAPbI₃. Solar cells based on (111)-α-FAPbI₃ demonstrate improved performance compared to the randomly oriented perovskite films treated by other antisolvents.

Abstract

Fabricating perovskite films with a dominant crystal orientation is an effective path to realizing quasi-single-crystal perovskite film, which can eliminate the fluctuation of the electrical properties in films arising from grain-to-grain variations, and improve the performance of perovskite solar cells (PSCs). Perovskite (FAPbI₃) films based on one-step antisolvent methods usually suffer from chaotic orientations due to the inevitable intermediate phase conversion from intermediates of PbI₂•DMSO, FA₂Pb₃I₈•4DMSO, and δ-FAPbI₃ to α-FAPbI₃. Here, a high-quality perovskite film with (111) preferred orientation ((111)-α-FAPbI₃) using a short-chain isomeric alcohol antisolvent, isopropanol (IPA) or isobutanol (IBA), is reported. The interaction between IPA and PbI₂ leads to a corner-sharing structure instead of an edge-sharing PbI₂ octahedron, sidestepping the formation of these intermediates. With the volatilization of IPA, FA⁺ can replace IPA in situ to form α-FAPbI₃ along the (111) direction. Compared to randomly orientated perovskites, the dominantly (111) orientated perovskite ((111)-perovskite) exhibits improved carrier mobility, uniform surface potential, suppressed film defects and enhanced photostability. PSCs based on the (111)-perovskite films show 22% power conversion efficiency and excellent stability, which remains unchanged after 600 h continuous working at maximum power point, and 95% after 2000 h of storage in atmosphere environment.

An effective interfacial defect and carrier management strategy is developed by synergistically modulating organic functional groups and spatial conformation of organic ammonium salt modification molecules. The 3-ammonium propionic acid iodide-modified device based on vacuum flash technology achieves an alluring peak efficiency of 24.72% (certified 23.68%), which is among highly efficient devices fabricated without antisolvents.

Abstract

Interfacial nonradiative recombination loss is a huge barrier to advance the photovoltaic performance. Here, one effective interfacial defect and carrier dynamics management strategy by synergistic modulation of functional groups and spatial conformation of ammonium salt molecules is proposed. The surface treatment with 3-ammonium propionic acid iodide (3-APAI) does not form 2D perovskite passivation layer while the propylammonium ions and 5-aminopentanoic acid hydroiodide post-treatment lead to the formation of 2D perovskite passivation layers. Due to appropriate alkyl chain length, theoretical and experimental results manifest that COOH and NH₃ ⁺ groups in 3-APAI molecules can form coordination bonding with undercoordinated Pb²⁺ and ionic bonding and hydrogen bonding with octahedron PbI₆ ⁴⁻, respectively, which makes both groups be simultaneously firmly anchored on the surface of perovskite films. This will strengthen defect passivation effect and improve interfacial carrier transport and transfer. The synergistic effect of functional groups and spatial conformation confers 3-APAI better defect passivation effect than 2D perovskite layers. The 3-APAI-modified device based on vacuum flash technology achieves an alluring peak efficiency of 24.72% (certified 23.68%), which is among highly efficient devices fabricated without antisolvents. Furthermore, the encapsulated 3-APAI-modified device degrades by less than 4% after 1400 h of continuous one sun illumination.

The interfacial chemistry of a single-molecule junction plays a pivotal role in determining the final charge-transport efficiency. Internal charge reorganisation is responsible for the observed behaviour, and the results provide a general, intuitive strategy for the structural design of efficient molecular wires.

Abstract

Most studies in molecular electronics focus on altering the molecular wire backbone to tune the electrical properties of the whole junction. However, it is often overlooked that the chemical structure of the groups anchoring the molecule to the metallic electrodes influences the electronic structure of the whole system and, therefore, its conductance. We synthesised electron-accepting dithienophosphole oxide derivatives and fabricated their single-molecule junctions. We found that the anchor group has a dramatic effect on charge-transport efficiency: in our case, electron-deficient 4-pyridyl contacts suppress conductance, while electron-rich 4-thioanisole termini promote efficient transport. Our calculations show that this is due to minute changes in charge distribution, probed at the electrode interface. Our findings provide a framework for efficient molecular junction design, especially valuable for compounds with strong electron withdrawing/donating backbones.

Tandem solar is attractive replacement to overcome the shortcomings of single-junction solar cells (SCs). This review summarizes various attractive top cell materials for silicon tandem SCs, highlights the fundamental challenges in way of commercialization, and describes the promising approaches and solutions that overcome these challenges and lead us toward terawatt era.

Silicon (Si) is a low-cost, stable photovoltaic market contributor which is approaching its single-junction theoretical efficiency limit. To further elevate the efficiency of crystalline Si (c-Si) afterward, Si solar cells (SCs) need a proper top cell absorber in Si tandem SCs. Herein, the top cell absorber is studied by evaluating their current state of the art, the existing challenges, and possible future solutions which can enhance their efficiency. The progress of perovskite/Si tandem SC both for monolithic and four terminals is exceptional but still many challenges limit their commercialization. In view of these challenges, the relative's solutions are prescribed in detail to make possible their realization. III–V semiconductors being mature candidates still face a growth/fabrication problem, which makes them a costly option for III–V/Si tandem SCs. Effective growth strategies along with technical solutions are discussed in detail. Emerging chalcogenides are considered the future of tandem technology. Recent developments in the chalcogenides/Si tandem SC are highlighted and the possible options are presented. In the end, a short note is given on the near future tandem materials for Si tandem SCs.

Efficient multifunctional anti-corrosive interface modification is developed with 2,2′-(1,3-phenylene)-bis[5-(4-tert-butylphenyl)-1,3,4-oxadiazole] (OXD-7). The OXD-7 strategy can tackle most of the cathode interface issues and a relatively higher power conversion efficiency of 21.84%, high fill factor of 84.63%, and excellent device stability are achieved in inverted perovskite solar cells based on a MAPbI₃/PCBM heterojunction.

Abstract

The interface stability and non-radiative recombination loss of the cathode interface greatly limit the stability and performance of inverted perovskite solar cells (PSCs). Here, an efficient multifunctional anti-corrosive interface modification strategy based on 2,2′-(1,3-phenylene)-bis[5-(4-tert-butylphenyl)-1,3,4-oxadiazole] (OXD-7) is proposed to overcome the cathode interface issues. OXD-7 molecules chemically coordinate to the Ag electrode and form a chemically stable complex film of OXD7-Ag, which suppresses halide ion migration and thus enhances the corrosion resistance of the electrode as well. In addition, the trap density of perovskite film, PCBM/Ag interfaces contact, the built-in potential, moisture resistance, as well as the unfavorable interface exciton dissociation elimination of the devices, are also improved with the OXD-7 arrangement upon PCBM film, which correspondingly enhances the device performance and stability. Bidirectional halide ion migration and the ITO corrosion are observed, which is also suppressed by the OXD-7 modification. The high power conversion efficiency (PCE) of 21.84% and the high fill factor (≈84.63%) is obtained via this strategy, which is one of the highest PCEs and FFs based on solution-process MAPbI₃/PCBM heterojunctions. The PCE can maintain ≈80% of its initial value after 1080 h at 85 °C with OXD-7 modification.

A symmetry–asymmetry dual-acceptor (SADA) strategy to construct ternary device is discussed. The employing of symmetric L8-BO and asymmetric BTP-S9 allows the ternary device delivers a high efficiency of 18.84% (certified result of 18.44%). In addition, asymmetric BTP-S9 with a larger dipole moment exhibits good crystalline properties, which enhances the intrinsic molecular photostability and further consolidates the operational lifetime of devices which feature L8-BO.

Abstract

Simultaneously achieving improvements in power conversion efficiency (PCE) and stability is the main task of the current development stage of organic solar cells (OSCs). This work reports a symmetry–asymmetry dual-acceptor (SADA) strategy to construct ternary devices, which is found to be feasible for increasing both the PCE and the operational lifetime of OSCs. In this contribution, the symmetric acceptor L8-BO and the asymmetric acceptor BTP-S9 are blended in equal proportions with polymer donor PM6 for the consideration of absorption spectrum complementarity and cascade energetic alignment. In addition, the features of crystallinity and miscibility of the dual-acceptor deliver optimized morphology lead to a high PCE of 18.84%. In addition, the asymmetric acceptor BTP-S9 with a larger dipole moment shows tighter molecular stacking and longer crystal correlation length, which favor intrinsic molecular photostability, and further consolidate the operational lifetime of OSCs when coordinated with L8-BO. This work demonstrates the efficacy of the SADA strategy for constructing efficient and stable OSCs.

Chlorinated PTB7-Th boostsperylene diimides (PDI)-based organic solar cells (OSCs), exceeding 10% efficiency. This is the highest power conversion efficiency (PCE) value with one of the lowest energy losses for OSCs based on PTB7-Th derivatives:PDI-type nonfullerene acceptors. The chlorinated side thienyl groups can elevate the charge-transfer state, reduce the degree of energetic disorder, and increase the electroluminescent quantum efficiency by two orders of magnitude, thus resulting in 0.103 eV lower nonradiative energy loss.

Abstract

The scarcity of narrow bandgap donor polymers matched with perylene diimides (PDI)-based nonfullerene acceptors (NFAs) hinders improvement of the power conversion efficiency (PCE) value of organic solar cells (OSCs). Here, it is reported that a narrow bandgap donor polymer PDX, the chlorinated derivative of the famous polymer donor PTB7-Th, blended with PDI-based NFA boosts the PCE value exceeding 10%. The electroluminescent quantum efficiency of PDX-based OSCs is two orders of magnitude higher than that of PTB7-Th-based OSCs;therefore, the nonradiative energy loss is 0.103 eV lower. This is the highest PCE value for OSCs with the lowest energy loss using the blend of PTB7-Th derivatives and PDI-based NFAs as the active layer. Besides, PDX-based devices showed larger phase separation, faster charge mobilities, higher exciton dissociation probability, suppressed charge recombination, elevated charge transfer state, and decreased energetic disorder compared with the PTB7-Th-based OSCs. All these factors contribute to the simultaneously improved short circuit current density, open circuit voltage, and fill factor, thus significantly improving PCE. These results prove that chlorinated conjugated side thienyl groups can efficiently suppress the non-radiative energy loss and highlight the importance of fine-modifying or developing novel narrow bandgap polymers to further elevate the PCE value of PDI-based OSCs.

Using DPI-TPFB as a dopant in Spiro-OMeTAD improves electrical conductivity by serving as a Lewis acid and also stabilizes Sn²⁺ ions by coordinating with them on the FASnI₃ surface. This dopant enables fabricating FASnI₃-based perovskite solar cells with 10.9% efficiency, and these devices retain 80% of their initial performance even after 1597 h under maximum power point tracking.

Abstract

Improving the performance, reproducibility, and stability of Sn-based perovskite solar cells (PSCs) with n–i–p structures is an important challenge. Spiro-OMeTAD [2,2′,7,7′-tetrakis(N,N-di-p-methoxyphenyl-amine)9,9′-spirobifluorene], a hole transporting material (HTM) with n–i–p structure, requires the oxygen exposure after addition of Li-TFSI [Lithium bis(trifluoromethanesulfonyl)imide] as a dopant to increase the hole concentration. In Sn-based PSC, Sn²⁺ is easily oxidized to Sn⁴⁺ under such a condition, resulting in a sharp decrease in efficiency. Herein, a formamidinium tin triiodide (FASnI₃)-based PSCs fabricated using DPI-TPFB [4-Isopropyl-4′-methyldiphenyliodonium tetrakis(pentafluorophenyl)borate] instead of Li-TFSI are reported as a dopant in Spiro-OMeTAD. The DPI-TPFB enables the fabrication of PSCs with an efficiency of up to 10.9%, the highest among FASnI₃-based PSCs with n–i–p structures. Moreover, ≈80% of the initial efficiency is maintained even after 1,597 h under maximum power point tracking conditions. In particular, the encapsulated device does not show any decrease in efficiency even after holding for 50 h in the 85 °C/85% RH condition. The high efficiency and excellent stability of PSCs prepared by doping with DPI-TPFB are attributed to not only increasing electrical conductivity by acting as a Lewis acid, but also stabilizing Sn²⁺ through coordination with Sn²⁺ on the surface of FASnI₃.

The pre-buried 3-aminopropionic acid hydroiodide (3AAH) into the electron transport layer (ETL) and modified the ETL/perovskite (PVK) interface by a bottom-up strategy. 3AAH treatment induces a templated perovskite grain growth and improves the quality of the ETL. By this, the residual stresses generated in PVK during the annealing-cooling process are released and converted into micro-compressive stresses, while reducing the defect density. The flexible device obtained an excellent power conversion efficiency of 23.36%.

Abstract

With rapid development of photovoltaic technology, flexible perovskite solar cells (f-PSCs) have attracted much attention for their light weight, high flexibility and portability. However, the power conversion efficiency (PCE) achieved so far is not yet comparable to that of rigid devices. This is mainly due to the great challenge of depositing homogeneous and high-quality perovskite films on flexible substrate. In this study, the pre-buried 3-aminopropionic acid hydroiodide (3AAH) additives into the electron transport layer (ETL) and modified the ETL/perovskite (PVK) interface by a bottom-up strategy. 3AAH treatment induced a templated perovskite grain growth and improved the quality of the ETL. By this, the residual stresses generated in PVK during the annealing-cooling process are released and converted into micro-compressive stresses. As a result, the defect density of f-PSCs with pre-buried 3AAH is reduced and the photovoltaic performance is greatly improved, reaching an exceptional PCE of 23.36%. This strategy provides a new idea to bridge the gap between flexible and rigid devices.