Stabilizing perovskite precursors with the reductive natural amino acid for printable mesoscopic perovskite solar cells

Solution processability significantly advances the development of highly-efficient perovskite solar cells.However,the precursor solution tends to undergo irreversible degradation reactions,impairing the device performance and reproducibility.Here,we utilize a reductive natural amino acid,Nacetylcysteine(NALC),to stabilize the precursor solution for printable carbon-based hole-conductorfree mesoscopic perovskite solar cells.We find that I_(2) can be generated in the aged solution containing methylammonium iodide(MI) in an inert atmosphere and speed up the MA-FA^(+)(formamidinium) reaction which produces large-size cations and hinders the formation of perovskite phase.NALC effectively stabilizes the precursor via its sulfhydryl group which reduces I_(2) back to I^(-)and provides H^(+).The NALC-stabilized precursor which is aged for 1440 h leads to devices with a power conversion efficiency equivalent to 98% of that for devices prepared with the fresh precursor.Furthermore,NALC improves the device power conversion efficiency from 16.16% to 18.41% along with enhanced stability under atmospheric conditions by modifying grain boundaries in perovskite films and reducing associated defects.

Tailored multifunctional hydrazine derivatives for efficient printable hole-conductive-free mesoscopic perovskite solar cells via enhancing defect passivation

The low-cost and easy large-scale fabrication advantages of printable mesoscopic perovskite solar cells(p-MPSCs)are overshadowed by their limited photovoltaic conversion efficiency(PCE).Here,we introduce the hydrazide derivative of 4-Hydroxybenzoylhydrazine(4-HBH)to improve the PCE of p-MPSCs by inducing enhanced defect passivation.Both carbonyl and hydrazine groups in hydrazide groups present strong interaction with perovskite.The hydroxyl group,as an electron donor group,increases the electron cloud density of the hydrazide group in 4-HBH under the conjugation of the benzene ring,and thus enhances its interaction with perovskite.Additionally,the hydroxy group itself interacts with perovskite and passivates defects synergistically.The hydrazine agents can also reduce I2and suppress the loss of iodine in perovskite films,which inhibits the formation of iodine-related defects.Consequently,p-MPSCs with 4-HBH achieve a high PCE of 19.21%,and present well improved stability.

SiO2 nanoparticle-regulated crystallization of lead halide perovskite and improved efficiency of carbon-electrode-based low-temperature planar perovskite solar cells

SiO2 nanoparticles were used to regulate the crystallizing process of lead halide perovskite films prepared by the sequential deposition method,which was used in the low-temperature-processed,carbon-electrode-basing,hole-conductor-free planar perovskite solar cells.It was observed that,after adding small amount of SiO2 precursor(1 vol%)into the lead iodide solution,performance parameters of open-circuit voltage,short-circuit current and fill factor were all upgraded,which helped to increase the power conversion efficiency(reverse scan)from 11.44(±1.83)%(optimized at 12.42%)to 14.01(±2.14)%(optimized at 15.28%,AM 1.5G,100 mW/cm^2).Transient photocurrent decay curve measurements showed that,after the incorporation of SiO2 nanoparticles,charge extraction was accelerated,while transient photovoltage decay and dark current curve tests both showed that recombination was retarded.The improvement is due to the improved crystallinity of the perovskite film.X-ray diffraction and scanning electron microscopy studies observed that,with incorporation of amorphous SiO2 nanoparticles,smaller crystallites were obtained in lead iodide films,while larger crystallites were achieved in the final perovskite film.This study implies that amorphous SiO2 nanoparticles could regulate the coarsening process of the perovskite film,which provides an effective method in obtaining high quality perovskite film.

Unveiling the effect of amino acids on the crystallization pathways of methylammonium lead iodide perovskites

Multifunctional additives are widely used to improve crystallization and to passivate defects in perovskite solar cells. The roles of these additives are usually related to the various functional groups contained in such additives. Here, we introduce a serious of analogues of amino acids into methylammonium lead iodide perovskites and find they play different roles in the crystallization process despite the fact that these additives share exactly the same terminal groups, namely one amino group and one carboxyl group. The corresponding crystallization pathways are established for the first time via monitoring the time-resolved phase formation and transformation. We find that avoiding the rapid formation of perovskites from precursor solution can facilitate the uniform nucleation and growth of perovskite crystals with enhanced crystallinity and reduced defects. Further, we find the different crystallization behaviors probably arise from the inherent structural characteristic of these additives, leading to different interactions in the precursors. This study unveils the effects of amino acids on the liquid–solid crystallization process and helps better understand the role of multifunctional additives beyond their functional groups.

超越传统光伏:弱光环境下可印刷介观钙钛矿太阳能电池光电特性

钙钛矿太阳能电池(perovskite solar cell,PSC)近年来发展十分迅速,被认为是下一代光伏技术中最有前景的候选者之一.其中,基于三层介孔膜结构的可印刷介观PSC以其廉价的原材料、简单的制备工艺以及良好的器件稳定性获得了广泛关注.本文测试了可印刷介观PSC小型模组(10 cm×10 cm)在不同光照强度条件下的光电性能,并与商用的单晶硅(crystalline silicon,c-Si)、多晶硅(polycrystalline silicon,poly-Si)和碲化镉(CdTe)太阳能电池进行了对比.结果表明,随着光照强度的降低,c-Si、poly-Si、CdTe太阳能电池的光电转换效率(power conversion efficiency,PCE)均出现了不同程度的下降,而可印刷介观PSC的PCE几乎呈线性增加.当光照强度低于0.3个标准太阳光(30 mW cm^(–2))时,可印刷介观PSC已经开始展现出一定的光电转换效率优势;当光照强度进一步降低至标准室内弱光条件(1000 lux,约0.3 mW cm^(–2))时,其PCE可达19.83%,高于其他商用太阳能电池.PSC在弱光环境下展现出的优异性能为进一步扩展其在室内等场景的应用奠定了良好基础,这些潜在的新兴应用领域为PSC的商业化和大规模生产提供了多种应用空间.

Influence of precursor concentration on printable mesoscopic perovskite solar cells

Over the last decade,the power conversion efficiency of hybrid organic-inorganic perovskite solar cells(PSCs)has increased dramatically from 3.8%to 25.2%.This rapid progress has been possible duc to the accurate control of the morphology and crystallinity of solution-processed perovskites,which are significantly affected by the concentration of the precursor used.This study explores the influence of precursor concentrations on the performance of printable hole-conductor-free meso-scopic PSCs via a simple one-step drop-coating method.The results reveal that lower concentrations lead to larger grains with inferior pore flling,while higher concentra-tions result in smaller grains with improved pore filling.Among concentrations ranging from 0.241.20M,devices based on a moderate strength of 0.70M were confirmed to exhibit the best efficiency at 16.32%.

Enhanced perovskite electronic properties via A-site cation engineering

Organic-inorganic halide perovskites have emerged as excellent candidates for low-cost photovoltaics and optoelectronics.While the predominant recent trend in designing perovskites for efficient and stable solar cells has been to mix different A-site cations,the role of A-site cations is still limited to tune the lattice and bandgap of perovskites.Herein we compare the optoelectronic properties of acetamidinum(Ace)and guanidinium(Gua)mixed methylammonium lead iodide perovskites and shed a light on the hidden role of A-site cation on the carrier mobility of mixed-cation lead iodide perovskites.The cations do not affect the bandgap of the perovskites since the orbitals from Ace and Gua do not contribute to the band edges of the material.However,the mobility of the Ace mixed perovskite is significantly enhanced to be an order of magnitude higher than that of the pristine perovskite.We apply the Ace mixed perovskite in hole-conductor-free printable mesoscopic perovskite solar cells and obtain a stabilized PCE of over 18%(certified 17.7%),which is the highest certified efficiency so far.

Screen printing process control for coating high throughput titanium dioxide films toward printable mesoscopic perovskite solar cells

Screen printing technique has been widely applied for the manufacturing of both traditional silicon solar cells and emerging photovoltaics such as dyesensitized solar cells(DSSCs)and perovskite solar cells(PSCs).Particularly,we have developed a printable mesoscopic PSC based on a triple layer scaffold of TiO2/ZrO2/carbon.The deposition of the scaftold is entirely based on screen printing process,which provides a promising prospect for low-cost photovoltaics.However,the optimal thickness of the TiO2 layer for fabricating efficient printable PSCs is much smaller than the typical thickness of screen printed films.Here,we tune the concentration of the pastes and the printing parameters for coating TiO?films,and successfully print TiO2 films with the thickness of 500-550 nm.The correlation between the thickness of the films and printing parameters such as the solid content and viscosity of the pastes,the printing speed and pressure,and the temperature has been investigated.Besides,the edge effect that the edge of the TiO2 films possesses a much larger thickness and printing positional accuracy have been studied.This work will significantly benefit the further development of printable mesoscopic PSCs.

Highly oriented MAPbI3 crystals for efficient hole-conductor-free printable mesoscopic perovskite solar cells

Highly crystalline perovskite films with large grains and few grain boundaries are conducive for efficient and stable perovskite solar cells.Current methods for preparing perovskite films are mostly based on a fast crystallization process,with rapid nucleation and insufficient growth.In this study,MAPbI3 perovskite with inhibited nucleation and promoted growth in the TiO_(2)/ZrO_(2)/carbon triple mesoscopic scaffold was crystallized by modulating the precursor and the crystallization process.N-methylformamide showed high solubility for both methylammonium iodide and Pbl2 and hampered the formation of large colloids in the MAPbI3 precursor solution.Furthermore,methylammonium chloride was added to reduce large colloids,which are a possible source of nucleation sites.During the crystallization of MAPbI3,the solvent was removed at a slow controlled speed,to avoid rapid nucleation and provide sufficient time for crystal growth.As a result,highly oriented MAPbI3 crystals with suppressed non-radiative recombination and promoted charge transport were obtained in the triple mesoscopic layer with disordered pores.The corresponding hole-conductor-free,printable mesoscopic perovskite solar cells exhibited a highest power conversion efficiency of 18.82%.The device also exhibited promising long-term operational sta-bility of 1000 h under continuous illumination at maximum power point at 55±5°C and damp-heat stability of 1340 h aging at 85°C as well as 85%relative humidity.