Chen Weijie

Nature Energy, Published online: 28 July 2022; doi:10.1038/s41560-022-01087-6

An ethanol soluble polymer PFO is developed. PFO-based organic photovoltaics assembled in air and via ethanol deliver a fine efficiency of 2.25% and preserve 45.24% of their initial efficiency after continuous illumination for 200 h. However, PFO-based devices present self-healing characteristics with remained efficiency increasing by 19.20% when undergoing intermittent illumination but with light-soaking time of 200 h.

Eco-friendly fabrication of organic solar cells (OSCs) via alcohol or water is highly desired for their cost-effective feature and benign profit for derived operators and ambient environment. Herein, a simple polyfuran derivative (PFO) that exhibits good solubility in ethanol/water solvent mixture is reported. Moreover, PFO displays broad optical absorption, high-lying electronic energy level, and large hole mobility. The air- and ethanol-processed PFO-based OSCs deliver a fine efficiency of 2.25%. Even though only 45.24% of their initial efficiency is preserved for optimized devices after continuous illumination for 200 h in ambient atmosphere, the remained efficiency value of optimized devices can increase by 19.20% when undergoing intermittent illumination yet for the same light-soaking time of 200 h. The self-healing efficiency of devices suffering from discontinuous illumination is associated with the partial dissolution and reconstruction of hydrogen bonds in active layer. The results provide important guidelines for designing electroactive materials for safe and environmentally benign fabrication of OSCs with self-sealing function.

Herein, a two-step annealing method in which solvent vapor annealing and thermal annealing are included is applied and 15% efficiency for block copolymer-based or single-component (called by some other peers) organic solar cells is achieved. This two-step annealing also pushes the nonhalogenated solvent-dissolved binary all-polymer solar cells toward >17% efficiency.

Block copolymer-based organic solar cells (OSCs) possess better stability than their binary all-polymer counterparts; thus, promoting the power conversion efficiency (PCE) of them to a higher level would be meaningful to achieving a higher level of efficiency–stability balance. Herein, two-step annealing combining solvent vapor and thermal annealing (TA) upon cast films is deployed and 15% efficiency for block copolymer PM6-b-PY-IT-based OSCs is realized, which appeals to the level of traditional binary all-polymer solar cells. The morphology optimization of the properly enhanced crystallite size, global crystallinity, and reduced pure phase length scale and maintained phase purity are supposed to be the driving force of increase device performance. This work offers a high PCE for the typical type of solar cell, brightening the prospect of realizing OSCs’ application.

Herein, fill factor roll-off of binary and ternary solar cells with the best power conversion efficiency of 11.6% is shown. By addition of a third component (ITIC-4F), an enhancement of photostability compared to the binary devices, PM6:ITIC-4F and PM6:ITIC-4Cl, is obtained. This is because the addition of a third component forms an acceptor cocrystal and inhibits the dissolution of ITIC-4Cl crystals.

The formation of photoinduced traps resulting in the loss of electron mobility deteriorates the performance of organic solar cells under continuous light soaking. The genesis of these loss mechanisms is elucidated by examining the structural stability of halogenated ITIC derivative films and the phase behavior of the respective binary systems by blending with the donor polymer PBDBT-2F. Under constant illumination, ITIC-4Cl is found to maintain its structural integrity, whereas fluorine on the peripheral moieties of ITIC-4F undergoes chemical substitution to form a mixture of ITIC and ITIC-4F. Thermal analysis of the light-soaked binary films reveals that ITIC-4Cl loses its crystalline phase while the crystallinity of ITIC-4F does not undergo changes. Further, it is shown that the addition of a small amount of ITIC-4F as a third component hinders the loss of ITIC-4Cl crystalline phase in bulk heterojunction blends through the formation of cocrystals. These results suggest that long-range ordering of NFAs does not necessarily improve the photostability of organic solar cells and that the addition of a third component, irrespective of the crystalline nature, can prevent changes in bulk heterojunction blend nanostructure.

By integrating Bi₂Te₃-based thermoelectric generator with all-inorganic CsPbBr₃ perovskite solar cell to form concentrator CsPbBr₃/Bi₂Te₃-integrated solar cell, a champion efficiency up to 12.46% with an ultrahigh open-circuit voltage of 2.114 V has been achieved by photovoltaic–thermoelectric principle under 5 suns irradiation owing to the full-spectra absorbance.

A solution to breaking through the Shockley–Queisser efficiency limit of solar cells is to increase the irradiation intensity beyond one standard sun by means of fabricating concentrator photovoltaics (CPVs). Herein, it is demonstrated that the power conversion efficiency (PCE) of carbon-electrode, all-inorganic CsPbBr₃ perovskite solar cell (PSC) can be enhanced to 10.08% under 5 suns from 8.94% under one sun. The efficiency improvement mainly contributes to the especially boosted open-circuit voltage (V _oc) up to 1.643 V, which is delivered by the high-irradiation enlarged quasi-Fermi-level splitting in CsPbBr₃ perovskite film. The substantially detrimental heat induced by carbon electrode owing to its full-spectral absorbance to light is further used by integrating a Bi₂Te₃ thermoelectric generator (TEG) into this all-inorganic CsPbBr₃ PSC to play the role of refrigerant under concentrated light condition. The CsPbBr₃/Bi₂Te₃-integrated device achieves a PCE of 12.46% with an ultrahigh V _oc of 2.114 V by the photovoltaic–thermoelectric principle. More importantly, the integrated solar cell maintains over 90% of the initial efficiency after 150 h irradiation under 5 suns, suggesting a great potential to enhance efficiency by fabricating integrated perovskite/thermoelectric devices.

The amino-functionalized carbon nanotube (NH₂-CNT) as both the crystal growth templates and the grain boundary passivator can anchor the perovskite crystal nuclear on the NH₂-CNT skeleton to modulate the grain growth and carrier behavior dynamics of perovskite films. A high power conversion efficiency (PCE) of 21.01% has been achieved in the PSCs based on MAPbI₃: NH₂-CNT film.

Simultaneously enlarging perovskite grain size and passivating grain boundary defects are highly desired for achieving a high photovoltaic performance of perovskite solar cells (PSCs). Herein, the amino-functionalized carbon nanotube (NH₂-CNT) is introduced into the perovskite precursor solution as both the crystal growth templates and the grain boundary passivator to modulate the grain growth and carrier behavior dynamics of perovskite films. The amino groups can anchor the perovskite crystal nuclear on the NH₂-CNT skeleton to obtain perovskite films with larger grain sizes. Moreover, the NH₂-CNT mainly located at the grain boundaries can not only effectively passivates the defects due to the strong interaction between amino group and perovskite, but also tunes the energy band alignment and provides a faster carrier transport channel to accelerate the electrons extraction and transfer process. As a result, the MAPbI₃-based PSCs with NH₂-CNT exhibit a power conversion efficiency of 21.01%. This work presents a promising strategy for fabricating efficient and stable PSCs by tuning perovskite films using environmentally friendly functionalized carbon materials.

An amine-free precursor consisting of zinc acetate dehydrate (ZAH) in methanol is proposed to prepare ZnO films. The temperature required for converting the precursor complex into ZnO was as low as 90 °C, which is substantially lower than that (over 120 °C) required for the traditional amine-containing precursor. Low-temperature-processed ZnO can function efficiently as an electron-transport layer in nonfullerene solar cells.

Abstract

Sol-gel-derived ZnO is one of the most widely used electron-transport layers in inverted organic solar cells. The sol-gel ZnO precursor consists of zinc acetate dehydrate (ZAH) and ethanolamine dissolved in 2-methoxyethanol, where ethanolamine chelates with ZAH, which helps ZAH dissolve in the 2-methoxyethanol. However, an annealing temperature above 120 °C is required to convert the complexes into ZnO. High temperatures are incompatible with flexible plastic substrates such as polyethylene terephthalate. In this work, we report an amine-free recipe consisting of ZAH in methanol to prepare ZnO films. The complex formed in the amine-free precursor solution is methanol-solvated ZAH, which is simpler than that of the amine-containing precursor solution. The temperature required for converting the precursor complex into ZnO was reduced to 90 °C for the amine-free recipe. Low-temperature-processed ZnO can function efficiently as an electron-transport layer in both rigid and flexible inverted nonfullerene solar cells.

New D _2h symmetric porphyrin hole-transporting materials were synthesized for high-efficiency perovskite solar cells. The best device based on MDA4 with two diphenylamino groups directly attached to the porphyrin core exhibited a power conversion efficiency of 22.67 % (certified value of 22.19 %) with exceptional thermal stability. The novel strategy paves the way for efficient and stable PSCs with porphyrin HTMs.

Abstract

A series of new D _2h symmetric porphyrins (MDA4, MTA4, and MDA8) with donor-π-donor structures have been synthesized as the hole-transporting materials for perovskite solar cells (PSCs). The novel porphyrin molecules feature a D _2h symmetrically substituted Zn^II porphyrin core and two kinds of donor systems (diarylamine (DAA) and triarylamine (TAA)), which can regulate energy level, increase thermal stability, solubility, and hydrophobicity via long alkoxyl chains. PSC devices based on MDA4 as the HTM showed impressive power-conversion efficiency (PCE) of 22.67 % under AM1.5G solar illumination. Notably, the device was sent for certification, and a PCE of 22.19 % was reported, representing the highest PCE from porphyrin-based HTMs. Furthermore, the MDA4-based PSCs showed excellent thermal stability under 60 °C and RH 60 % and preserved 88 % of initial performance after 360 hours. The strategy opens a new avenue for developing efficient and stable porphyrin HTMs for PSCs.

N-tert-butyl-2-benzothiazolesulfenamide (TBBS) is added to the PbI₂ precursor solution and thermally decomposes to yield volatile tert-butylamine, which volatilizes during annealing to induce porous PbI₂. On front layer of perovskite, S-H combines with uncoordinated Pb²⁺ and branches of hydrophobic PTAA fill MA⁺ vacancies on back layer to achieve synergistic passivation, enhancing the stability of device.

Moisture stability is one of the key factors that hinders the commercialization of perovskite solar cells (PSCs). Herein, a new method of front and back layer synergistic passivation of perovskite is investigated. On the front layer, porous PbI₂ nanostructures are induced by N-tert-butyl-2-benzothiazolesulfenamide (TBBS), which is added into PbI₂ precursor solution and thermally decomposed to tert-butylamine (TBA) and 2-mercaptobenzothiazole (2-MBT) during annealing process. TBA volatilization leaves voids to induce porous PbI₂, promoting diffusion of organic salts, facilitating crystallization of perovskite. Thickness of perovskite with TBBS doping increases from 527.7 to 561.2 nm, and the champion power conversion efficiency (PCE) increases from 19.71% to 20.97%. On the back layer, hydrophobic hole transport material PTAA is introduced onto perovskite surface to fill cation vacancies. Eventually, the highest efficiency of 22.35% with outstanding moisture stability is achieved after front and back layer synergistic passivation, which can maintain 71.14% of its initial efficiency after 7 days under high relative humidity (RH = 65 ± 2%) in ambient conditions without any encapsulation, while the control one can only remain 12.38%.

Herein, ultrathin ZrO₂ is deposited on the mesoporous TiO₂ surface of fully printable mesoscopic perovskite solar cells by using spray pyrolysis. Thanks to surface lattice perturbation of Zr⁴⁺, reduction of surface oxygen vacancies of TiO₂ decreases density of defective states at TiO₂-perovskite interface inhibiting Shockly-Read-Hall recombination. Based on perovskite Cs_0.05(FA_0.92MA_0.08)_0.95Pb(I_0.92Br_0.08)₃, a high power conversion efficiency of 17.81% is obtained.

For carbon-based fully printable mesoscopic perovskite solar cells (FP-PSCs), due to the serious interfacial defects formed in the uncontrollable crystallization process, modifying the interface between perovskite and electron transport layer is an effective way to enhance their photovoltaic performance. Herein, ultrathin ZrO₂ is deposited on the mesoporous TiO₂ surface by using spray pyrolysis, and Zr⁴⁺ intercalates into the TiO₂ surface lattice and works together with Ti⁴⁺ and O²⁻ ions. Thanks to this surface lattice perturbation of Zr⁴⁺, the reduction of surface oxygen vacancies of TiO₂ (electron transport layer) decreases the density of defective states at the TiO₂–perovskite interface inhibiting the Shockley–Read–Hall recombination (nonradiative recombination) in the charge cross-interface transfer. Furthermore, both the open-circuit voltage and short-circuit current density are improved significantly. Based on perovskite Cs_0.05(FA_0.92MA_0.08)_0.95Pb(I_0.92Br_0.08)₃ for carbon-based FP-PSCs, a high power conversion efficiency of 17.81% is obtained. It provides a novel idea and technology for efficient interfacial modification of the electron transport layer for FP-PSCs.

A synchronous strategy consisting of surface reconstruction and defect control for fabricating high-performance inorganic CsPbI_{3− x} Br _x perovskite solar cells (PSCs) is demonstrated. The power conversion efficiency is significantly increased from 18.43% to 20.40%, making it one of the most efficient inorganic PSCs. Furthermore, the optimized devices exhibit better environmental stability.

Abstract

The nonradiative charge recombination caused by surface defects and inferior crystalline quality are major roadblocks to further enhancing the performance of CsPbI_{3− x} Br _x perovskite solar cells (PSCs). Theoretical calculations indicate that sodium diethyldithiocarbamate (NaDDTC), a popular bacteriostatic benign material, can initiate multiple interactions with the CsPbI_{3− x} Br _x perovskite surface to effectively passivate the defects. The experimental results reveal that the NaDDTC can indeed passivate the electron trap states and lock active sites for charge traps and water adsorption. In addition, it is found that a solid-state reaction is triggered for perovskite crystal regrowth by the NaDDTC post-treatment, which not only enlarges grain size for reducing the density of grain boundary defects but also compensates some surface defects induced by the primary film growth. Consequently, the power conversion efficiency (PCE) of the CsPbI_{3− x} Br _x PSC is increased to as high as 20.40%, with significant improvement in fill factor and open-circuit voltage (V _OC), making it one of the highest for this type of solar cell. Furthermore, the optimized devices exhibit better environmental stability. Overall, this robust synchronous strategy provides efficient surface reconstruction and defect passivation for achieving both high PCE and stable inorganic perovskite.

Modification of the ITIC backbone by selenium or halogen atoms can modulate the polarity of the IC group end, thus inducing molecular assembly as 2D brickwork or 3D web structures.

Abstract

The current research investigates the structure features and intermolecular interactions of nonfullerene acceptors (NFAs) in single crystal and thin films, as well as their solar cell applications. Guiding parameters and key intermolecular forces that lead to 2D brickwork or 3D web packing are identified. The atomic modification is shown as the key to induce hydrogen bonding or π–π stacking column, which results in different crystalline packing. The molecular assembly in thin film is initiated by hydrogen bonding, and completed by π–π stacking reorganization. The packing energy is seen as a guiding parameter that dictates the NFA crystalline morphology in blended thin films. The crystalline packing motif is not directly related with device efficiency. However, the crystalline morphology is the key parameter to influence exciton/carrier dynamics and device performance. A broader picture on the scaling behavior of organic semiconductor crystals ranging from oligoacenes to NFAs is established.

N-benzyloxycarbonyl-d-valine is demonstrated to be a simple surface post-treatment material to improve the grain sizes, crystallinity, trap states, cathode interfaces, built-in field as well as [6,6]-phenyl-C₆₁-butyric acid methyl ester film formation for perovskite solar cells. A relatively higher power conversion efficiency of 21.80% and good stability are obtained in the MAPbI₃-based inverted perovskite solar cells.

Abstract

Defects in perovskite films and the suboptimal interface contact largely limit the performance and stability of inverted perovskite solar cells (PSCs). A simple surface post-treatment with N-benzyloxycarbonyl-d-valine (NBDV) is developed to overcome these problems. The device performance following NBDV treatment is systemically investigated. It is showed that NBDV surface post-treatment results in the bulk restructure of the entire perovskite film and improves the film-forming property of [6,6]-phenyl-C₆₁-butyric acid methyl ester. The grain sizes, crystallinity, trap states, cathode interfaces, as well as the built-in field are also improved, which result in PSC performance and stability enhancement. A relatively higher power conversion efficiency (PCE) of 21.80% is reached, which is comparable to the PCE record based on single-crystal MAPbI₃. Meanwhile, the PCE of the NBDV devices can retain ≈77% and 84% of the initial value after storage for 768 h (32 days) in air and 8376 h (349 days) in N₂, respectively, while the control devices only maintain ≈53% and 38% of their initial PCE values under the same exposure conditions. This work provides means to promote bulk, surface, and interface regulation toward high performance and stable inverted PSCs.

Brominated polythiophene, prepared via a novel and simple two-step approach, can markedly reduce the energy level of polythiophenes and modulate their molecular stacking, therefore facilitating charge transport in quantum dot/organic heterojunctions. Accordingly, the performance of hybrid solar cells is boosted from ≈8.7% to a benchmark of ≈11% (26% increase), which is to date the highest value in this field.

Abstract

The emerging solution-processed solar cells have attracted worldwide effort in the last decade. Developing efficient, stable, and cost-effective solar cells is strongly desirable in countering the growing global warming. Nevertheless, the photovoltaic performance and stability of hybrid solar cells based on low-cost polythiophenes are far from satisfactory, due to their high-lying energy levels and excessive aggregation. Herein, it is shown that brominated polythiophene (P3HT-Br), prepared via a facile two-step approach can effectively facilitate charge transport and suppress recombination in quantum dot (QD)/organic heterojunctions. Accordingly, the power conversion efficiency of the optimized hybrid polythiophene/QD cell is boosted from 8.7% to 11% (a 26% increase) with markedly reduced energy loss. More strikingly, the device achieves record-high thermal stability with a lifetime of over 400 h maintaining 80% of the initial performance. Both device efficiency and stability are the best reported for polythiophene/QD hybrid solar cells. Moving forward, brominated polythiophenes hold great application in perovskite solar cells with significantly improved performance and offer new opportunities for other emerging solar cells.

E. Ruggeri, M. Anaya, K. Gałkowski, A. Abfalterer, Y.-H. Chiang, K. Ji, Z. Andaji-Garmaroudi, S. D. Stranks

Mixed-cation mixed-halide perovskite compositions represent a promising route toward achieving stable and efficient solar cells. Here, the structural evolution of these absorber layers during full device operation is investigated via operando X-ray diffraction techniques. A stabilizing compressive strain effect leading to the remixing of the halide population is unveiled, providing insight into new strategies toward increased device lifetimes and stability.

Mixed-halide mixed-cation hybrid perovskites are among the most promising perovskite compositions for application in a variety of optoelectronic devices due to their high performance, low cost, and bandgap-tuning capabilities. Instability pathways such as those driven by ionic migration, however, continue to hinder their further progress. Here, an operando variable-pitch synchrotron grazing-incidence wide-angle X-ray scattering technique is used to track the surface and bulk structural changes in mixed-halide mixed-cation perovskite solar cells under continuous load and illumination. By monitoring the evolution of the material structure, it is demonstrated that halide remixing along the electric field and illumination direction during operation hinders phase segregation and limits device instability. Correlating the evolution with directionality- and depth-dependent analyses, it is proposed that this halide remixing is induced by an electrostrictive effect acting along the substrate out-of-plane direction. However, this stabilizing effect is overwhelmed by competing halide demixing processes in devices exposed to humid air or with poorer starting performance. The findings shed new light on understanding halide de- and re-mixing competitions and their impact on device longevity. These operando techniques allow real-time tracking of the structural evolution in full optoelectronic devices and unveil otherwise inaccessible insights into rapid structural evolution under external stress conditions.

Heterogenous seeding-induced crystallization is introduced to assist perovskite growth. Di-tert-butyl(methyl)phosphonium tetrafluoroborate is introduced into the precursor to form a low-solubility complex with PbI₂, which serve as seed to induce perovskite crystallization during solvent evaporation. The hetero-SiC process is a proven effective way to manipulate the nucleation process and crystal growth, visualized by several in situ measurement tools.

Abstract

The addition of small seeding particles into a supersaturated solution is one among the most effective approaches to obtain high-quality semiconductor materials via increased crystallization rates. However, limited study is conducted on this approach for the fabrication of perovskite solar cells. Here, a new strategy—“heterogenous seeding-induced crystallization (hetero-SiC)” to assist the growth of FAPbI₃-based perovskite is proposed. In this work, di-tert-butyl(methyl)phosphonium tetrafluoroborate is directly introduced into the precursor, which forms a low-solubility complex with PbI₂. The low-solubility complex can serve as the seed to induce crystallization of the perovskite during the solvent-evaporation process. Various in situ measurement tools are used to visualize the hetero-SiC process, which is shown to be an effective way of manipulating the nucleation and crystal growth of perovskites. The hetero-SiC process greatly improves the film quality, reduces film defects, and suppresses nonradiative recombination. A hetero-SIC proof-of-concept device exhibits outstanding performance with 24.0% power conversion efficiency (PCE), well over the control device with 22.2% PCE. Additionally, hetero-SiC perovskite solar cell (PSC) stability under light illumination is enhanced and the PSC retains 84% of its initial performance after 1400 h of light illumination.

Nature Materials, Published online: 25 July 2022; doi:10.1038/s41563-022-01311-4

Publication date: 17 August 2022

Source: Joule, Volume 6, Issue 8

Author(s): Yuan Gao, Renxing Lin, Ke Xiao, Xin Luo, Jin Wen, Xu Yue, Hairen Tan

Publication date: 17 August 2022

Source: Joule, Volume 6, Issue 8

Author(s): Minyong Du, Shuai Zhao, Lianjie Duan, Yuexian Cao, Hui Wang, Youming Sun, Likun Wang, Xuejie Zhu, Jiangshan Feng, Lu Liu, Xiao Jiang, Qingshun Dong, Yantao Shi, Kai Wang, Shengzhong (Frank) Liu

Nature Energy, Published online: 21 July 2022; doi:10.1038/s41560-022-01076-9