Tongle Bu

A novel quadruple-cation absorber for universal hysteresis elimination for high efficiency and stable perovskite solar cells

Organic–inorganic metal halide perovskite solar cells (PSCs) have made a striking breakthrough with a power conversion efficiency (PCE) over 22%. However, before moving to commercialization, the hysteresis of PSCs, characterized as an inconsistent photovoltaic conversion property at varied electric fields, should be eliminated for stable performance. Herein, we present a novel quadruple-cation perovskite absorber, KxCs0.05(FA0.85MA0.15)0.95Pb(I0.85Br0.15)3 (labeled as KCsFAMA), with which the hysteresis in PSCs can be fully eliminated irrespective of the electron transportation layers. The incorporation of potassium intensively promotes the crystallization of the perovskite film with a grain size up to ∼1 μm, doubled compared to the K free counterparts. Further characterization revealed that a lower interface defect density, longer carrier lifetime and fast charge transportation have all made contributions to the hysteresis-free, stable and high PCE (20.56%) of the KCsFAMA devices. Moreover, we present a 6 × 6 cm2 sub-module with the KCsFAMA composition achieving a high efficiency of 15.76% without hysteresis. This result suggests that the quadruple-cation perovskite is a highly attractive candidate for future developments of efficient and stable PSC modules.

Non‐Conjugated Polymer as an Efficient Dopant‐Free Hole‐Transporting Material for Perovskite Solar Cells

A new non-conjugated polymer (PVCz-OMeDAD) with good solution processability was developed to serve as an efficient dopant-free hole-transporting material (HTM) for perovskite solar cells (PSCs). PVCz-OMeDAD was simply prepared by the free-radical polymerization of vinyl monomers, which were synthesized from low-cost raw materials through three high-yield synthesis steps. The combination of the flexible non-conjugated polyvinyl main chain and hole-transporting methoxydiphenylamine-substituted carbazole side chains endowed PVCz-OMeDAD with excellent film-forming ability, a suitable energy level, and high hole mobility. As a result, by using an ultra-thin (≈30 nm) PVCz-OMeDAD film as cost-effective dopant-free polymer HTM, the conventional n-i-p-type PSCs demonstrated a power conversion efficiency (PCE) up to 16.09 %, suggesting the great potential of the polymer film for future low-cost, large-scale, flexible PSCs applications.

Robust transparent superamphiphobic coatings on non-fabric flat substrates with inorganic adhesive titania bonded silica

The technological implementation of superamphiphobic surfaces has been largely hindered by the stability issues caused by surface abrasion, corrosion, contamination, etc. Robustness still remains the major challenge for a well-performing superamphiphobic coating. In this study, the simple route of spraying inks containing pre-designed silica, cetyltrimethylammonium bromide (CTAB) and titanium diisopropoxide bis-2,4-pentanedionate (TAA) is presented to prepare micro–nanostructure films. The mechanical properties of the films are significantly strengthened by titania after the pyrogenic decomposition of TAA, and the films are able to withstand a standard 2H pencil scratching and sand flow impact. The as-made films exhibit excellent super-repellency to various liquids after treatment with 1H,1H,2H,2H-perfluorodecyltrichlorosilane (PFTS). The static contact angles (SCAs) for water (surface tension 72.1 mN m−1) and dodecane (surface tension 25.3 mN m−1) can reach 166° ± 3° and 153° ± 3°, respectively. On controlling the thickness of the films, the optical transmittance of the films (400 nm thick) can come close to that of glass. Moreover, efficient photocatalytic decomposition of an organic substance attached on the surfaces is demonstrated; this decomposition enables the recovery of the superamphiphobic property of the contaminated films. Thus, the unique properties of robustness, transparency and self-healing, etc., combined with the relatively low cost fabrication, make these superamphiphobic coatings promising in various applications.

Improved air stability of perovskite hybrid solar cells via blending poly(dimethylsiloxane)–urea copolymers

A new kind of PDMS–urea co-polymer has been synthesized and successfully incorporated into the fabrication process of perovskite solar cells. Such a polymer possesses both a flexible and hydrophobic PDMS backbone and urea groups capable of hydrogen binding. Scanning electron microscopy showed that the morphology of the perovskite layer was greatly improved after addition of 10 mg ml−1 PDMS–urea into perovskite precursor solution. As a result, the short circuit current of the devices was improved by 10% and the energy conversion efficiency by 27%, reaching 16.15% under 1 sun simulated sunlight. Steady-state photoluminescence spectra reveal a much improved photoluminescence intensity after the introduction of PDMS–urea into the perovskite layer. The devices with the perovskite-PDMS–urea (20 mg ml−1) hybrid demonstrate an almost unchanged efficiency for 2500 h, proving its remarkable effect on improving the stability of perovskite solar cells.

Ultrasonic Spray-Coating of Large-Scale TiO2 Compact Layer for Efficient Flexible Perovskite Solar Cells

Flexible electronics have attracted great interest in applications for the wearable devices. Flexible solar cells can be integrated into the flexible electronics as the power source for the wearable devices. In this work, an ultrasonic spray-coating method was employed to deposit TiO2 nanoparticles on polymer substrates for the fabrication of flexible perovskite solar cells (PSCs). Pre-synthesized TiO2 nanoparticles were first dispersed in ethanol to prepare the precursor solutions with different concentrations (0.5 mg/mL, 1.0 mg/mL, 2.0 mg/mL) and then sprayed onto the conductive substrates to produce compact TiO2 films with different thicknesses (from 30 nm to 150 nm). The effect of the different drying processes on the quality of the compact TiO2 film was studied. In order to further improve the film quality, titanium diisopropoxide bis(acetylacetonate) (TAA) was added into the TiO2-ethanol solution at a mole ratio of 1.0 mol % with respect to the TiO2 content. The final prepared PSC devices showed a power conversion efficiency (PCE) of 14.32% based on the indium doped tin oxide coated glass (ITO-glass) substrate and 10.87% on the indium doped tin oxide coated polyethylene naphthalate (ITO-PEN) flexible substrate.

Organic/inorganic self-doping controlled crystallization and electronic properties of mixed perovskite solar cells

Organic and inorganic molecules/atoms located at different lattice positions in hybrid perovskite films play various roles in crystallization and carrier transport for perovskite films. For efficient and stable solar devices, high quality crystals and the proper dispersion of organic/inorganic species are required. In a preferably mixed perovskite system (a blend of MA, FA, I, Br, etc.), however, the effects of inorganic/organic ratios on the performances and electrical properties of perovskite solar cells have not been fully understood. Here, we present perovskite solar cells with self-doped organic and inorganic components to investigate in detail their effect on crystallization and electrical properties. The organic component enhances the conductivity and reduces the hysteresis, while the inorganic component promotes crystal growth. A critical composition is beneficial to perovskite crystallization, with larger crystals and a pinhole-free morphology, and the corresponding device achieved a high efficiency over 19.14% (0.16 cm2, mask area) and 16.2% at an area of 1.21 cm2. Thus, evaluation of the organic/inorganic variation effects provides an understanding of self-doping in mixed perovskites and is beneficial to pursue high-performance perovskite devices.

Low-Temperature Presynthesized Crystalline Tin Oxide for Efficient Flexible Perovskite Solar Cells and Modules

Organic-inorganic metal halide perovskite solar cells (PSCs) have been emerging as one of the most promising next generation photovoltaic technologies with a breakthrough power conversion efficiency (PCE) over 22%. However, aiming for commercialization, it still encounters challenges for the large-scale module fabrication, especially for flexible devices which have attracted intensive attention recently. Low-temperature processed high-performance electron-transporting layers (ETLs) are still difficult. Herein, we present a facile low-temperature synthesis of crystalline SnO2 nanocrystals (NCs) as efficient ETLs for flexible PSCs including modules. Through thermal and UV-ozone treatments of the SnO2 ETLs, the electron transporting resistance of the ETLs and the charge recombination at the interface of ETL/perovskite were decreased. Thus, the hysteresis-free highly efficient rigid and flexible PSCs were obtained with PCEs of 19.20 and 16.47%, respectively. Finally, a 5 × 5 cm2 flexible PSC module with a PCE of 12.31% (12.22% for forward scan and 12.40% for reverse scan) was fabricated with the optimized perovskite/ETL interface. Thus, employing presynthesized SnO2 NCs to fabricate ETLs has showed promising for future manufacturing.

Efficient and stable mixed perovskite solar cells using P3HT as a hole transporting layer

Inorganic–organic hybrid perovskite solar cells (PSCs) have drawn great attention in the past several years. As the stability of PSCs has been a major obstacle for their commercialization, a lot of work has been focused on improving the long-term stability. Here, we reported a meso-structured mixed PSC employing poly(3-hexylthiophene-2,5-diyl) (P3HT) as a hole transport layer (HTL) showing a stable performance even after one year of exposure to air. The impact of different HTL thicknesses on the power conversion efficiency (PCE) of the PSCs has been investigated. The performance of the PSCs was further improved by doping Li-salt/4-tert-butylpyridine into the P3HT HTL. A maximum PCE of 17.55% was achieved, superior to the 14.30% PCE of the pristine P3HT-based devices. The effect of the dopants on the stability of the devices has also been studied.

A helical perylene diimide-based acceptor for non-fullerene organic solar cells: synthesis, morphology and exciton dynamics

Helical perylene diimide-based (hPDI) acceptors have been established as one of the most promising candidates for non-fullerene organic solar cells (OSCs). In this work, we report a novel hPDI-based molecule, hPDI2-CN2, as an electron acceptor for OSCs. Combining the hPDI2-CN2 with a low-bandgap polymeric donor (PTB7-Th), the blending film morphology exhibited high sensitivity to various treatments (such as thermal annealing and addition of solvent additives), as evidenced by atomic force microscope studies. The power conversion efficiency (PCE) was improved from 1.42% (as-cast device) to 2.76% after thermal annealing, and a PCE of 3.25% was achieved by further addition of 1,8-diiodooctane (DIO). Femtosecond transient absorption (TA) spectroscopy studies revealed that the improved thin-film morphology was highly beneficial for the charge carrier transport and collection. And a combination of fast exciton diffusion rate and the lowest recombination rate contributed to the best performance of the DIO-treated device. This result further suggests that the molecular conformation needs to be taken into account in the design of perylene diimide-based acceptors for OSCs.

Enhanced Crystallinity of Low-Temperature Solution-Processed SnO2 for Highly Reproducible Planar Perovskite Solar Cells

Low-temperature solution-processed SnO2 as a promising electron-transport material for planar perovskite solar cells (PSCs) has attracted particular attention because of its outstanding properties such as high optical transparency or high electron mobility. However, low-temperature sol-gel processes used in the synthesis are inevitably affected by the humidity of the atmosphere, which results in a wide distribution in the performance of the prepared PSCs owing to the inability to control crystallinity and defects. Herein, a highly crystalline SnO2 film is synthesized using a simple water bath post-treatment, which can remove the surface residuals of SnCl4 on the SnO2 films, which is beneficial for the interface charge transport from the perovskite to the SnO2 electron-transport layer. An improved performance of the PSCs can be easily obtained applying this treatment, giving rise to a high power conversion efficiency (PCE) of 19.17 %, much higher than that of the pristine SnO2 -based device (17.59 %). Most importantly, the reproducibility of the devices has been greatly improved, independent of the environmental humidity. Therefore, the enhanced crystallinity of SnO2 has shown promise for future commercial PSC applications: 5 cm×5 cm PSC modules have achieved a PCE of 16.16 %.