wangzhaowei

Benzylamine is introduced as a surface passivation molecule that improves the moisture-resistance of the perovskites while simultaneously enhancing their electronic properties. Solar cells based on benzylamine-modified formamidinium lead iodide perovskite films exhibit a champion efficiency of 19.2% and an open-circuit voltage of 1.12 V. The modified FAPbI₃ films exhibit no degradation after >2800 h air exposure.

The addition of Sr²⁺ in CH₃NH₃PbI₃ perovskite films enhances the charge carrier collection efficiency of solar cells leading to very high fill factors, up to 85%. The charge carrier lifetime of Sr²⁺-containing perovskites is in excess of 40 μs, longer than those reported for perovskite single crystals.

Side-chain fluorination of polymers is demonstrated as a highly effective strategy to improve the efficiency of all-polymer solar cells from 2.93% (nonfluorinated P1) to 7.13% (fluorinated P2). This significant enhancement is achieved by synergistic improvements in open-circuit voltage, charge generation, and charge transport, as fluorination of the donor polymer optimizes the band alignment and the film morphology.

Two different nonfullerene acceptors and one copolymer are used to fabricate ternary organic solar cells (OSCs). The two acceptors show unique interactions that reduce crystallinity and form a homogeneous mixed phase in the blend film, leading to a high efficiency of ≈10.3%, the highest performance reported for nonfullerene ternary blends. This work provides a new approach to fabricate high-performance OSCs.

Hybrid halide perovskite solar cells generally show differences in the power output depending on the voltage sweep direction, an undesired phenomenon termed hysteresis. Although the causes of this behavior have not yet been univocally determined, commonly, hysteresis heavily affects solar cells based on flat TiO₂ as electron extracting layer. Herein, it is shown how perovskite material quality has a preeminent impact on hysteresis, and how combined deposition and post-deposition engineered manufacturing could lead to highly efficient and hysteresis-less solar cells, notwithstanding a planar TiO₂-based layout. This methodology relies on solvent engineering during the casting process, leading to an ultra-flat, uniform, and thick film ensuring an optimal interface connection with the charge-extracting layer combined with post-deposition thermal and vacuum treatments, which merge the crystalline domains and cure the defects at the grain boundaries. This method allows obtaining perovskite active layer with superior optical properties, explaining the ideal device behavior and performances, therefore, a simple optimization of perovskite processing conditions can efficiently stem hysteresis targeting different device layouts. Power conversion efficiency of 15.4% and reduced hysteresis are achieved.

Perovskite material quality has a preeminent impact on hysteresis. The presented method relies on solvent engineering during the casting process, leading to a thick film that ensures an optimal interface connection with the charge-extracting layer. This method allows obtaining perovskite active layer with superior optical properties, explaining the ideal device behavior and device performances.

In this work, different from the commonly explored strategy of incorporating a smaller cation, MA⁺ and Cs⁺ into FAPbI₃ lattice to improve efficiency and stability, it is revealed that the introduction of phenylethylammonium iodide (PEAI) into FAPbI₃ perovksite to form mixed cation FA_xPEA_1–xPbI₃ can effectively enhance both phase and ambient stability of FAPbI₃ as well as the resulting performance of the derived devices. From our experimental and theoretical calculation results, it is proposed that the larger PEA cation is capable of assembling on both the lattice surface and grain boundaries to form quais-3D perovskite structures. The surrounding of PEA⁺ ions at the crystal grain boundaries not only can serve as molecular locks to tighten FAPbI₃ domains but also passivate the surface defects to improve both phase and moisture stablity. Consequently, a high-performance (PCE:17.7%) and ambient stable FAPbI₃ solar cell could be developed.

The introduction of a bulkier phenylethylammonium cation into FAPbI₃ is revealed to effectively enhance both phase and ambient stability of FAPbI₃. The larger hydrophobic cation is proposed to assemble on lattice surface and grain boundaries to form quasi-3D perovskite structures, which tightens FAPbI₃ domains and passivates surface defects, leading to a efficient and stable FAPbI₃ based solar cell.

The stability of single-crystalline/monocrystalline-like perovskite film is expected to be better than its microcrystalline counterparts. In the present work, highly orientated perovskite thin films (CH₃NH₃PbI_3–xCl_x) are prepared by means of aquointermediates assisted solution process. It displays super-duper preferred-orientation along <110> direction that is close to the single crystal, and its diffraction intensity ratio of (110)/(310) is nearly two orders of magnitude higher in contrast to the films that prepared by traditional way. Owing to its superior performances, e.g., highly crystallized quality, stress-free inside films, longer electron lifetime, faster temporal response time, etc., the highly orientated perovskite-based solar cells accordingly allow realizing high efficiency while improving its thermal stability.

Highly orientated perovskite thin films (CH₃NH₃PbI_3–xCl_x) are prepared by means of aquointermediate assisted one-step solution process. It demonstrates monocrystalline-like performances, e.g., extremely high preferred-orientation, stress-free inside films, longer electron lifetime, lower defect density, and faster temporal response time. The highly orientated perovskite-based solar cells allow realizing the efficiency as high as 16.9% while improving its thermal stability.

The chemical structure of conjugated polymers plays an important role in determining their physical properties that, in turn, dictates their performance in photovoltaic devices. 5-Fluoro-2,1,3-benzothiadiazole, an asymmetric unit, is incorporated into a thiophene-based polymer backbone to generate a hole conducting polymers with controlled regioregularity. A high dipole moment is seen in regioregular polymers, which have a tighter interchain stacking that promotes the formation of a morphology in bulk heterojunction blends with improved power conversion efficiencies. Aliphatic side chain substitution is systematically varied to understand the influence of side chain length and symmetry on the morphology and resultant performance. This side chain modification is found to influence crystal orientation and the phase separated morphology. Using the asymmetric side chain substitution with regioregularity of the main chain, an optimized power conversion efficiency of 9.06% is achieved, with an open circuit voltage of 0.72 V, a short circuit current of 19.63 mA cm⁻², and a fill factor over 65%. These results demonstrate that the local chemical environment can dramatically influence the physical properties of the resultant material.

The unidirectional regioregular conjugated polymers using 5-fluoro-2,1,3-benzothiadiazole (FBT) asymmetric unit were synthesized. Compared with the regiorandom control polymers, the regioregular polymers with a unidirectional fluorine atom alignment can lead to a progressive dipole moment along the backbone. The regioregular FBT polymers exhibit tighter interchain stacking and better morphology in bulk heterojunction blends, giving rise to improved power conversion efficiency.

The large energy loss (>0.6 eV) in polymer solar cells (PSCs) is limiting the improvement of photovoltage. In article number 1600148, Xiaofeng Xu, Wei Ma, Ergang Wang, and co-workers report that a low band gap (1.49 eV) polymer attains a high photovoltage of 1.0 V with efficiency of 6.7% in PSCs. It represents an impressively low energy loss of 0.49 eV, which challenges the current paradigm and reveals the potential to further enhance the performance of PSCs.

Solution-based perovskite solar cell fabrication typically involves rather complex processing sequences to yield highest performance. While most studies concentrate on the exploration of processing conditions, the purity levels of common perovskite precursor solutions have been investigated and a number of impurities that are critically important toward controlling the crystallization of perovskites are found. In this study, an in-depth chemical study of the possible impurities formed during CH₃NH₃I preparation is presented and their relevance on solar cell processing is revealed. A primary consideration is the chemical transformation of hypophosphorous acid, which plays the role of the stabilizer for HI. The detrimental role of the impurities is best demonstrated by comparing perovskite solar cell devices fabricated from impurity-free precursors versus precursors containing different concentrations of impurities. Most interestingly, it is revealed that a certain concentration of impurities is detrimental to the growth of large-grained crystals. PbHPO₃ nanoparticles, which are formed after hypophosphorous acid transformation, actually cause crystal domain growth through serving as a nucleation center. This study gives valuable insight into the rate determining steps of perovskite crystal growth and further provides the basis for developing reliable and reproducible high-performance recipes for perovskite solar cell processing.

A chemical study of the impurities formed during CH₃NH₃I preparation and their impact on solar cell processing is reported. These impurities initiate PbHPO₃ nanoparticles formation in the perovskite precursor solution, with further seed growth of grains. The detrimental role of the impurities is best demonstrated by comparing perovskite solar cell devices fabricated from impurity-free precursors versus precursors containing different concentrations of impurities.

Carbon nanotubes have a variety of remarkable electronic and mechanical properties that, in principle, lend them to promising optoelectronic applications. However, the field has been plagued by heterogeneity in the distributions of synthesized tubes and uncontrolled bundling, both of which have prevented nanotubes from reaching their full potential. Here, a variety of recently demonstrated solution-processing avenues is presented, which may combat these challenges through manipulation of nanoscale structures. Recent advances in polymer-wrapping of single-walled carbon nanotubes (SWNTs) are shown, along with how the resulting nanostructures can selectively disperse tubes while also exploiting the favorable properties of the polymer, such as light-harvesting ability. New methods to controllably form nanoengineered SWNT networks with controlled nanotube placement are discussed. These nanoengineered networks decrease bundling, lower the percolation threshold, and enable a strong enhancement in charge conductivity compared to random networks, making them potentially attractive for optoelectronic applications. Finally, SWNT applications, to date, in organic and perovskite photovoltaics are reviewed, and insights as to how the aforementioned recent advancements can lead to improved device performance provided.

The state of the art in functionalized single-walled carbon nanotubes (SWNTs) and conductive networks for opto-electronic applications is reviewed. An outlook on new strategies for enhancing charge extraction and transport in photovoltaic systems incorporating SWNTs is discussed, including organic photovoltaics and the new field of perovskite-based photovoltaics.

Small-molecule nonfullerene-based tandem organic solar cells (OSCs) are fabricated for the first time by utilizing P3HT:SF(DPPB)₄ and PTB7-Th:IEIC bulk heterojunctions as the front and back subcells, respectively. A power conversion efficiency of 8.48% is achieved with an ultrahigh open-circuit voltage of 1.97 V, which is the highest voltage value reported to date among efficient tandem OSCs.

Organic solar cells hold promise of providing low-cost, renewable power generation, with current devices providing up to 13% power conversion efficiency. The rational design of more performant systems requires an in-depth understanding of the interactions between the electron donating and electron accepting materials within the active layers of these devices. Here, we explore works that give insight into the intermolecular interactions between electron donors and electron acceptors, and the impact of molecular orientations and environment on these interactions. We highlight, from a theoretical standpoint, the effects of intermolecular interactions on the stability of charge carriers at the donor/acceptor interface and in the bulk and how these interactions influence the nature of the charge transfer states as well as the charge separation and charge transport processes.

An assessment of intermolecular interactions and their impact on electronic processes in organic solar cells is presented. While a great deal has been learned about the molecular-scale optical and electronic processes in these devices, a complete understanding of how the active-layer composition and morphology influence the charge transfer states, polarization and charge separation still needs to be reached.

All-polymer solar cells (all-PSCs) utilizing p-type polymers as electron-donors and n -typepolymers as electron-acceptors have attracted a great deal of attention, and their efficiencies have been improved considerably. Here, five polymer donors with different molecular orientations are synthesized by random copolymerization of 5-fluoro-2,1,3-benzothiadiazole with different relative amounts of 2,2′-bithiophene (2T) and dithieno[3,2-b;2′,3′-d]thiophene (DTT). Solar cells are prepared by blending the polymer donors with a naphthalene diimide-based polymer acceptor (PNDI) or a [6,6]-phenyl C₇₁-butyric acid methyl ester (PC₇₁BM) acceptor and their morphologies and crystallinity as well as optoelectronic, charge-transport and photovoltaic properties are studied. Interestingly, charge generation in the solar cells is found to show higher dependence on the crystal orientation of the donor polymer for the PNDI-based all-PSCs than for the conventional PC₇₁BM-based PSCs. As the population of face-on-oriented crystallites of the donor increased in PNDI-based PSC, the short-circuit current density (J_SC) and external quantum efficiency of the devices are found to significantly improve. Consequently, device efficiency was enhanced of all-PSC from 3.11% to 6.01%. The study reveals that producing the same crystal orientation between the polymer donor and acceptor (face-on/face-on) is important in all-PSCs because they provide efficient charge transfer at the donor/acceptor interface.

Five polymer donors showing different molecular orientations are synthesized by carrying out random copolymerization, and their photovoltaic properties are investigated by fabricating all-polymer solar cells using a PNDI polymer acceptor. As compared with PC₇₁BM-based devices, charge generation in the PNDI-based devices is found to be highly dependent on the orientation of the polymer donor.