Highly Efficient and Stable FAPbI_(3) Perovskite Solar Cells and Modules Based on Exposure of the(011)Facet

Perovskite crystal facets greatly impact the performance and stability of their corresponding photovoltaic devices.Compared to the(001)facet,the(011)facet yields better photoelectric properties,including higher conductivity and enhanced charge carrier mobility.Thus,achieving(011)facet-exposed films is a promising way to improve device performance.However,the growth of(011)facets is energetically unfavorable in FAPbI_(3) perovskites due to the influence of methylammonium chloride additive.Here,1-butyl-4-methylpyridinium chloride([4MBP]Cl)was used to expose(011)facets.The[4MBP]^(+)cation selectively decreases the surface energy of the(011)facet enabling the growth of the(011)plane.The[4MBP]^(+)cation causes the perovskite nuclei to rotate by 45°such that(011)crystal facets stack along the out-of-plane direction.The(011)facet has excellent charge transport properties and can achieve better-matched energy level alignment.In addition,[4MBP]Cl increases the activation energy barrier for ion migration,suppressing decomposition of the perovskite.As a result,a small-size device(0.06 cm2)and a module(29.0 cm2)based on exposure of the(011)facet achieved power conversion efficiencies of 25.24%and 21.12%,respectively.

The Main Progress of Perovskite Solar Cells in 2020-2021

Perovskite solar cells(PSCs)emerging as a promising photovoltaic technology with high efficiency and low manufacturing cost have attracted the attention from all over the world.Both the efficiency and stability of PSCs have increased steadily in recent years,and the research on reducing lead leakage and developing eco-friendly lead-free perovskites pushes forward the commercialization of PSCs step by step.This review summarizes the main progress of PSCs in 2020 and 2021 from the aspects of efficiency,stability,perovskite-based tandem devices,and lead-free PSCs.Moreover,a brief discussion on the development of PSC modules and its challenges toward practical application is provided.

Improving the performance of arylamine-based hole transporting materials in perovskite solar cells： Extending π-conjugation length or increasing the number of side groups？

In this work, we prepared three simple arylamine-based hole transporting materials from commercially available starting materials. The effect of extending z-conjugation length or increasing the number of side groups compared with reference compound on the photophysical, electrochemical, hole mobility properties and performance in perovskite solar cells were further studied. It is noted that these two kinds of molecular modifications can significantly lower the HOMO level and improve the hole mobility, thus improving the hole injection from valence band of perovskite. On the other hand, the compound with more side groups showed higher hole injection efficiency due to lower HOMO level and higher hole mo- bility compared with the compound with extending π-conjugation length. The perovskite solar cells with the modified molecules as hole transporting materials showed a higher efficiency of 15.40% and 16.95%, respectively, which is better than that of the reference compound （13.18%）. Moreover, the compound with increasing number of side groups based devices showed comparable photovoltaic performance with that of conventional spiro-OMeTAD （16.87%）.

Enlarging grain sizes for efficient perovskite solar cells by methylamine chloride assisted recrystallization

The quality of MAPbI3 film prepared by solvent engineering process highly depends on environment and antisolvent control.Here,we provided a simple methylamine chloride(MACl)solution treatment using a two-step process to enlarge the perovskite crystal grain sizes to more than 1 lm.Other than treatment on the film surface,the MACl solution diffuses into the MAPbI_(3) films to assist the recrystallization of small crystal at the bottom of perovskite film.The imitative contact between perovskite and substrate is formed.Meanwhile,the enlargement of grain size and ten times enhancement of crystalline reduce trap-assisted recombination of perovskite films.Thus,the significant improvement of cell efficiency of 20.89%as well as device stability is obtained with the MACl treatment.

Molecular-dynamics investigation of the simple droplet critical wetting behavior at a stripe pillar edge defect

The microscopic stripe pillar is one of the most frequently adopted building blocks for hydrophobic substrates. However, at high temperatures the particles on the droplet surface readily evaporate and re-condense on the pillar sidewall,which makes the droplet highly unstable and undermines the overall hydrophobic performance of the pillar. In this work,molecular dynamics(MD) simulation of the simple liquid at a single stripe pillar edge defect is performed to characterize the droplet's critical wetting properties considering the evaporation–condensation effect. From the simulation results, the droplets slide down from the edge defect with a volume smaller than the critical value, which is attributed to the existence of the wetting layer on the stripe pillar sidewall. Besides, the analytical study of the pillar sidewall and wetting layer potential field distribution manifests the relation between the simulation parameters and the degree of the droplet pre-wetting, which agrees well with the MD simulation results.

Heteroatom engineering on spiro-type hole transporting materials for perovskite solar cells

A series of spiro-type hole transporting materials, spiro-OMe TAD, spiro-SMe TAD and spiro-OSMe TAD,with methoxy, methylsulfanyl or half methoxy and half methylsulfanyl terminal groups are designed and prepared. The impact of varied terminal groups on bulk properties, such as photophysical, electrochemical, thermal, hole extraction, and photovoltaic performance in perovskite solar cells is investigated.It is noted that the terminal groups of the hole transporting material with half methoxy and half methylsulfanyl exhibit a better device performance and decreased hysteresis compared with all methoxy or methylsulfanyl counterparts due to better film-forming ability and improved hole extraction capability.Promisingly, the spiro-OSMe TAD also shows comparable performance than high-purity commercial spiro-OMe TAD. Moreover, the highest power conversion efficiency of the optimized device employing spiro-OSMe TAD exceeding 20% has been achieved.

C≡N-based carbazole-arylamine hole transporting materials for perovskite solar cells: Substitution position matters

Hole transporting materials(HTMs)containing passivating groups for perovskite materials have attracted much attention for efficient and stable perovskite solar cells(PSCs).Among them,C≡N-based molecules have been proved as efficient HTMs.Herein,a series of novel C≡N functionalized carbazole-arylamine derivatives with variable C≡N substitution positions(para,meta,and ortho)on benzene-carbazole skeleton(on the adjacent benzene of carbazole)were synthesized(p-HTM,m-HTM and o-HTM).The experimental results exhibit that the substitution positions of the Ctriple bondN unit on HTMs have minor difference on the HOMO energy level and hydrophobicity.m-HTM has a relatively lower glass transition temperature compared with that of p-HTM and o-HTM.The functional theory calculations show that the C≡N located on meta position exposed very well,and the exposure direction is also the same with the methoxy.Upon applying these molecules as HTMs in PSCs,their device performance is found to sensitively depend on the substitution position of the C≡N unit on the molecule skeleton.The devices using m-HTM and o-HTM exhibit better performance than that of p-HTM.Moreover,m-HTM-based devices exhibit better light-soaking performance and long-term stability,which could be resulted from better interaction with the perovskite according to DFT results.Moreover,we further prepared a HTM with two C≡N units on the symmetrical meta position of molecular skeleton(2m-HTM).Interestingly,2m-HTM-based devices exhibit relatively inferior performance compared with that of the m-HTM,which could be resulted from weak negative electrical character of C≡N unit on 2m-HTM.The results give some new insights for designing ideal HTM for efficient and stable PSCs.

Pyridine-triphenylamine hole transport material for inverted perovskite solar cells

In the light of superior interaction between pyridine unit and perovskite,a facile star-shaped triphenylamine-based hole transport material(HTM)incorporating pyridine core(coded as H-Pyr)is designed and synthesized.A reference HTM with benzene core,coded as H-Ben,is also prepared for a comparative study.The effects of varying core on HTMs are investigated by comparing the photophysical,electrochemical and hole mobility properties.It is found that pyridine core exhibits better conjunction and decreased dihedral angles with triphenylamine side arms than that of benzene,leading to obviously better hole mobility and well-matched work function.The perovskite film prepared on H-Pyr also shows improved crystallization than on H-Ben.Photoluminescence and electrochemical impedance studies indicate improved charge extraction and reduced recombination in the H-Pyr-based perovskite solar cells.Consequently,H-Pyr-based device exhibits higher efficiency than H-Ben-based one.After doping with a Lewis acid,tris(pentafluorophenyl)borane,H-Pyr-based device delivers a champion efficiency of 17.09%,which is much higher compared with 12.14% of the device employing conventional poly(3,4-ethy lenedioxythiophene)polystyrene sulfonate(PEDOT:PSS)as HTM.Moreover,the H-Pyr-based device displays good long-term stability that the power conversion efficiency remains over 80% of the initial value after storage in ambient(relative humidity=50±5%)for 20 days.

Inside-out Ostwald ripening： A facile process towards synthesizing anatase TiO2 microspheres for high- efficiency dye-sensitized solar cells

A facile inside-out Ostwald ripening route to the morphology-controlled preparation of TiO2 microspheres is developed. Here, TiO2 hollow microspheres （HM） and solid microspheres （SM） are prepared by adjusting the volume ratio of isopropanol （IPA） to acetylacetone （Acac） in the solvothermal process. During the formation process of HM, precipitation of solid cores, subsequent deposition of outer shells on the surface of cores, and simultaneous core dissolution and shell recrystallizafion are observed, which validate the inside-out Ostwald ripening mechanism. Design and optimization of the properties （pore size, surface area, and trap state） of TiO2 microspheres are vital to the high performance of dye- sensitized solar cells （DSSCs）. The optimized TiO2 rnicrospheres （rHM and rSM） obtained by post-processing on recrystallization, possess large pore sizes, high surface areas and reduced trap states （Ti3~ and oxygen vacancy）, and are thus ideal materials for photovoltaic devices. The power conversion efficiency of DSSCs fabricated using rHM photoanode is 11.22%, which is significantly improved compared with the 10.54% efficiency of the rSM-based DSSC. Our work provides a strategy for synthesizing TiO2 microspheres that simultaneously accommodate different physical properties, in terms of surface area, crystallinity, morphology, and mesoporosity.

New-type highly stable 2D/3D perovskite materials:the effect of introducing ammonium cation on performance of perovskite solar cells

Perovskite solar cells(PSCs) have drawn wide attention due to the rapidly rising efficiency which presently attains over 23%. However, problems of instability continue to plague the high-efficiency devices impairing their practical applications. Here, by firstly introducing smaller-size NH4+ into(FAPbI3)0.85(MAPbBr3)0.15(FA/MA) to form a novel 2D-3D mixed structure, we designed and prepared new-type hybrid perovskite materials of [(NH4)2.4(FA)n-1PbnI3n+1.4]0.85(MAPbBr3)0.15(n=3, 5, 7, 9 and 11)(A/FA/MA) and used them as absorber in solar cells. Especially, unlike the reported 2D/MD perovskite perovskites based on larger-size ammonium salts;A/FA/MA perovskites are the first to display red-shift light absorption and decreased band gaps in comparison to normal perovskites. Consequently, when n=9, the A/FA/MA device shows outstanding performance with a solar to electric power conversion efficiency(PCE) of 18.25% and negligible hysteresis. When the encapsulated A/FA/MA perovskite device was soaked in full sunlight for 1,000 h, the PCE remains almost unchanged. Moreover, the unsealed A/FA/MA PSCs maintain 90% of their initial PCE when aged at high humidity conditions over the same 1000-h time period. Our findings provide a guide for the future development of such novel perovskites and it is helpful to select more suitable ammonium salt to obtain highly efficient and stable 2D-3D PSCs.

Self-assembled α-MnO2 urchin-like microspheres as a high-performance cathode for aqueous Zn-ion batteries

Aqueous Zn-ion batteries(AZIBs)are one of the promising battery technologies for the green energy storage and electric vehicles.As one attractive cathode material for AZIBs,α-MnO2 materials exhibit superior electrochemical properties.However,their long-term reversibility is still in great suspense.Considering the decisive effect of the structure and morphology on theα-MnO2 materials,hierarchicalα-MnO2 materials would be promising to improve the cycle performance of AZIB.Here,we synthesized theα-MnO2 urchin-like microspheres(AUM)via a self-assembled method.The porous microspheres composed of one-dimensionalα-MnO2 nanofibers with high crystallinity,which improved the surface area and active sites for Zn2+intercalation.The AUM-based AZIB realized a high initial capacity of 308.0 mA hg-1,and the highest energy density was 396.7 W hkg-1.The kinetics investigation confirmed the high capacitive contribution and fast ion diffusion of the AUM.Ex-situ XRD measurement further verified the synergistic insertion/extraction of H+and Zn2+ions during the charge/discharge process.The superiority of the AUM guaranteed good electrochemical performance and reversible phase evolution,and this application would promote the follow-up research on the advanced AZIB.

Elucidating the dynamics of solvent engineering for perovskite solar cells

Researchers working in the field of photovoltaic are exploring novel materials for the efficient solar energy conversion.The prime objective of the discovery of every novel photovoltaic material is to achieve more energy yield with easy fabrication process and less production cost features.Perovskite solar cells (PSCs)delivering the highest efficiency in the passing years with different stoichiometry and fabrication modification have made this technology a potent candidate for future energy conversion materials.Till now,many studies have shown that the quality of active layer morphology,to a great extent,determines the performance of PSCs.The current and potential techniques of solvent engineering for good active layer morphology are mainly debated using primary solvent,co-solvent (Lewis acid-base adduct approach)and solvent additives.In this review,the dynamics of numerously reported solvents on the morphological characteristics of PSCs active layer are discussed in detail.The intention is to get a clear understanding of solvent engineering induced modifications on active layer morphology in PSC devices via different crystallization routes.At last,an attempt is made to draw a framework based on different solvent coordination properties to make it easy for screening the potent solvent contender for desired PSCs precursor for a better and feasible device.

Surface states in TiO2 submicrosphere films and their effect on electron transport

Owing to their special three-dimensional network structure and high specific surface area,TiO2 submicrospheres have been widely used as electron conductors in photoanodes for solar cells.In recent years,utilization of TiO2 submicrospheres in solar cells has greatly boosted the photovoltaic performance.Inevitably,however,numerous surface states in the TiO2 network affect electron transport.In this work,the surface states in TiO2 submicrospheres were thoroughly investigated by charge extraction methods,and the results were confirmed by the cyclic voltammetry method.The results showed that ammonia can effectively reduce the number of surface states in TiO2 submicrospheres.Furthermore,in-depth characterizations indicate that ammonia shifts the conduction band toward a more positive potential and improves the interfacial charge transfer.Moreover,charge recombination is effectively prevented.Overall,the cell performance is essentially dependent on the effect of the surface states,which affects the electron transfer and recombination process.

Advanced partial nucleation for single-phase FA0.92MA0.08PbI3-based high-efficiency perovskite solar cells

To date, extensive research has been carried out,with considerable success, on the development of highperformance perovskite solar cells(PSCs). Owing to its wide absorption range and remarkable thermal stability, the mixedcation perovskite FAxMA1-xPbI3(formamidinium/methylammonium lead iodide) promises high performance. However, the ratio of the mixed cations in the perovskite film has proved difficult to control with precursor solution. In addition, the FAxMA1-xPbI3 films contain a high percentage of MA+and suffer from serious phase separation and high trap states, resulting in inferior photovoltaic performance. In this study, to suppress phase separation, a post-processing method was developed to partially nucleate before annealing, by treating the as-prepared intermediate phase FAI-Pb I2-DMSO(DMSO: dimethylsulfoxide) with mixed FAI/MAI solution. It was found that in the final perovskite, FA0.92MA0.08 PbI3, defects were substantially reduced because the analogous molecular structure initiated ion exchange in the post-processed thin perovskite films, which advanced partial nucleation. As a result, the increased light harvesting and reduced trap states contributed to the enhancement of open-circuit voltage and short-circuit current. The PSCs produced by the post-processing method presented reliable reproducibility, with a maximum power conversion efficiency of 20.80% and a degradation of ~30% for 80 days in standard atmospheric conditions.

BiVO_4 semiconductor sensitized solar cells

Semiconductor sensitized solar cells(SSSCs) are promising candidates for the third generation of cost-effective photovoltaic solar cells and it is important to develop a group of robust, environment-friendly and visible-light-responsive semiconductor sensitizers. In this paper, we first synthesized bismuth vanadate(Bi VO4) quantum dots by employing facile successive ionic layer adsorption and reaction(SILAR) deposition technique, which we then used as a sensitizer for solar energy conversion. The preliminary optimised oxide SSSC showed an efficiency of 0.36%, nearly 2 orders of magnitude enhancement compared with bare Ti O2, due to the narrow bandgap absorption of Bi VO4 quantum dots and intimate contact with the oxide substrate. This result not only demonstrates a simple method to prepare Bi VO4 quantum dots based solar cells, but also provides important insights into the low bandgap oxide SSSCs.

Boosting optoelectronic performance of MAPbI3 perovskite solar cells via ethylammonium chloride additive engineering

The quality of the perovskite light absorption layer plays a dynamic role in the photovoltaic properties of solar cells.The existing methods to prepare methylammonium lead iodide(MAPbI3)films render substantial structural defect density,particularly at the grain boundaries and film surface,constituting a challenge that hinders the further optoelectronic enhancement of perovskite solar cells.Herein,a unique approach was introduced:using a simple ethylammonium chloride(EACl)additive in perovskite precursor mixture to produce high-quality MAPbI3 thin films.The results indicated that EACl could encourage perovskite crystal growth without experiencing the intermediate phase formation and would evaporate from the perovskite after annealing.Additionally,a gradient perovskite structure was achieved using this technique,which impressively enhanced the performance of the perovskite films.A high power conversion efficiency(PCE)of 20.03%was achieved under the optimal amount of EACl,and the resultant efficient device could retain over 89%of the original PCE after aging for 1000 h at room temperature.This novel technique leads to a facile fabrication of highquality and less-defect perovskite thin films for competent and stable devices.

Photo-stable perovskite solar cells with reduced interfacial recombination losses using a CeO interlayer

Despite demonstrating remarkable power conversion efficiencies(PCEs), perovskite solar cells(PSCs) have not yet achieved their full potential. In particular, the interfaces between the perovskite and charge transport layers account for the vast majority of the recombination losses.Interfacial contact and band alignment between the lowtemperature-processed TiO_(2) electron transport layer(ETL)and the perovskite are essential to minimize nonradiative recombination losses. In this study, a CeOx interlayer is employed to modify the perovskite/TiO_(2) interface, and the charge transport properties of the devices are investigated. The bilayer-structured TiO_(2)/CeOx ETL leads to the modification of the interface energetics, resulting in improved electron extraction and reduced nonradiative recombination in the PSCs.Devices based on TiO_(2)/CeOx ETL exhibit a high open-circuit voltage(Voc) of 1.13 V and an enhanced PCE of more than 20%as compared with Vocof 1.08 V and a PCE of approximately 18% for TiO^(2-)based devices. Moreover, PSCs based on TiO_(2)/CeOx ETL maintain over 88% of their initial PCEs after light illumination for 300 min, whereas PSCs based on TiO_(2) ETL almost failed. This study provides an efficient strategy to enhance the PCE and stability of PSCs based on a lowtemperature-processed TiO_(2) ETL.

Synergistic effect of TiO_2 hierarchical submicrospheres for high performance dye-sensitized solar cells

The performance of dye-sensitized solar cells(DSCs) could be improved by using rationally designed mesoporous film structure for electron collection, dye adsorption and light scattering. The development of a novel double layer film prepared by TiO_2 hierarchical submicrospheres and nanoparticles was reported in this article. The submicrospheres were composed of rutile nanorods of 10 nm diameter and the length of 150–250 nm, which facilitated fast electron transport, charge collection and light scattering. Using a double layer structure consisting of the 10 wt% film as a dye loading layer and the 50 wt% film as the light scattering layer, C101 sensitizer and liquid electrolyte, DSC yielded power conversion efficiency of 9.68% under 1 sun illumination.

Application of facile solution-processed ternary sulfide Ag_8SnS_6 as light absorber in thin film solar cells

Light absorber is critical to the further applications of thin film solar cells. Here, we report a facile solution-processed method with an annealing temperature below250°C to fabricate Ag8 SnS6(ATS) light absorber for thin film solar cells. After optimization, the ATS-based thin film solar cells exhibited a reproducible power conversion efficiency(PCE) of about 0.25% and an outstanding long-term stability with 90% of the initial PCE retained after a more than 1,000 h degradation test. This research revealed the potential application of ATS as an earth-abundant, low toxic and chemically stable light absorber in thin film solar cells.