Seed-assisted growth for high-performance perovskite solar cells:A review

The rapid increase in the power conversion efficiency(PCE)of perovskite solar cells(PSCs)is closely related to the development of deposition techinique for perovskite layer.The high-quality perovskite film enables efficient charge transportation and less trap states,which are eventually translated into enhanced device performance.Seed-assisted growth(SAG)is a potential technique for depositing highly-crystallized perovskite films with preferential crystal orientation among the numerous approaches related to crystallization modulation.In this review,we summarize the recent advances in the SAG technique for both one-step and two-step processed perovskite films.Additionally,seeding at the buried interface and on the top surface are also introduced.We present different seeds and their corresponding seeding mechanism in detail,such as inorganic nanomaterials,organic ammoniums,alkali metal halides,and perovskite seeds.Finally,challenges and perspectives are proposed to investigate the potential expansion of seeding engineering in high-performance PSCs,particularly large-area devices.

Nickel oxide for perovskite tandem solar cells

Perovskite tandem solar cells(TSCs)are popular for their ability to surpass the Shockley-Queisser(S-Q)limit of singlejunction solar cells[1-9].Currently,there are mainly four types of perovskite TSCs,including perovskite/silicon,perovskite/copper indium gallium selenide(CIGS).

Recent Advances in Wide-Bandgap Organic-Inorganic Halide Perovskite Solar Cells and Tandem Application

Perovskite-based tandem solar cells have attracted increasing interest because of its great potential to surpass the Shockley-Queisser limit set for single-junction solar cells.In the tandem architectures,the wide-bandgap(WBG)perovskites act as the front absorber to offer higher open-circuit voltage(VOC)for reduced thermalization losses.Taking advantage of tunable bandgap of the perovskite materials,the WBG perovskites can be easily obtained by substituting halide iodine with bromine,and substituting organic ions FA and MA with Cs.To date,the most concerned issues for the WBG perovskite solar cells(PSCs)are huge VOC deficit and severe photo-induced phase separation.Reducing VOC loss and improving photostability of the WBG PSCs are crucial for further efficiency breakthrough.Recently,scientists have made great efforts to overcome these key issues with tremendous progresses.In this review,we first summarize the recent progress of WBG perovskites from the aspects of compositions,additives,charge transport layers,interfaces and preparation methods.The key factors affecting efficiency and stability are then carefully discussed,which would provide decent guidance to develop highly efficient and stable WBG PSCs for tandem application.

Adjusting energy level alignment between HTL and CsPbI_(2)Br to improve solar cell efficiency

Lead halide perovskites are at the forefront of optoelectronic materials due to their high absorption coefficient,tunable bandgap,long carrier diffusion length,and small exciton binding energy[1−3],yielding high-performance optoelectronic devices.

Efficient and photostable CsPbI_(2) Br solar cells realized by adding PMMA

Organic–inorganic hybrid perovskite materials demonstrate promising applications in high-efficiency perovskite solar cells (PSCs) with a certified power conversion efficiency(PCE) of 25.5%(https://www.nrel.gov/pv/cell-efficiency.html).

Major strategies for improving the performance of perovskite solar cells

Metal halide perovskite solar cell(PSC)has successfully distinguished itself in optoelectronic field by virtue of the sharp rise in power conversion efficiency over the past decade.The remarkable efficiency breakthrough at such a fast speed can be mainly attributed to the comprehensive study on film deposition techniques,especially the effective management of surface and interfacial defects in recent works.Herein,we summarized the current trends in performance enhancement for PSCs,with a focus on the generally applicable strategies in high-performance works,involving deposition methods,compositional engineering,additive engineering,crystallization manipulation,charge transport material selection,interfacial passivation,optical coupling effect and constructing tandem solar cells.Promising directions and perspectives are also provided.

Defects in perovskite crystals

Perovskite solar cell(PSC) is now a shining star in photovoltaics field[1].Benefiting from excellent optoelectronic properties of perovskite materials,the certified power conversion efficiency(PCE)of PSCs has reached 26.0%[2],showing great potential for commercialization.In essence,the efficiency of solar cells is determined by the radiative and nonradiative recombination of photogenerated charge carriers.The unfavorable nonradiative recombination mainly assisted by the trap states leads to severe charge carrier loss and thus unsatisfactory efficiency.

Organic ammonium halides enhance the performance of Pb-Sn perovskite solar cells

With the efforts of scientists around the world,the power conversion efficiency(PCE)of perovskite solar cells(PSCs)has reached 25.7%.To further improve the efficiency and break through the Shockley-Queisser(S-Q)limit,it is promising to construct all-perovskite tandem solar cells via combining wide-bandgap and narrow-bandgap perovskites[1−5].As the key light-harvesting material for the bottom cell in all-per-ovskite tandem devices,the narrow-bandgap Pb-Sn mixed per-ovskites have attracted increasing interest in recent years[6−8].However,the Pb-Sn mixed perovskites suffer from uncontrol-lable crystallization,easy oxidation of Sn2+and high defect density,which significantly limit PCE improvement[9,10].Organ-ic ammonium halides can improve the efficiency and stabil-ity of Pb-Sn mixed PSCs.

CsPbI_(2.25)Br_(0.75) solar cells with 15.9% ef?ciency

Organic-inorganic perovskite (ABX3) solar cells (PSCs) have attracted wide interest in recent years (1)The power conversion efficiency (PCE) has increased up to 23.7%(NREL Best Research-Cell Efficiency Chart, https://www.nrel.gov/pv/cell-efficiency.html.

Low-temperature processed inorganic hole transport layer for efficient and stable mixed Pb-Sn low-bandgap perovskite solar cells

Metal halide perovskite solar cells(PSCs)have attracted tremendous attention as an emerging photovoltaic technology due to their high efficiency,low cost and ease of fabrication from earth-abundant materials[1,2].The power conversion efficiencies(PCEs)have been rapidly boosted from 3.8%in the pioneer’s work to a certified 24.2%nowadays in just ten years[3].The PCE breakthroughs in PSCs have mostly adopted full lead-based perovskites(APbX3)with bandgaps of 1.5–1.6 eV.

Thiolactone copolymer donor gifts organic solar cells a 16.72% efficiency

Since 1995,bulk-heterojunction organic solar cells consisting of one or two organic donors and one or two organic acceptors have been fighting for high power conversion efficiencies(PCEs)and good stability[1].Until recent years,this next-generation photovoltaic technology starts to offer decent PCEs,shedding the light on commercialization,and attracting great attention again[2-14].Compared w让h the continuously emerging highperformance nonfullerene acceptors,high-performance donors are rare.

Interface engineering gifts CsPbI2.25Br0.75 solar cells high performance

Organic-inorganic halide perovskite (ABX3) solar cells (PSCs)have made great progress in recent years [1]. The power conversion efficiency (PCE) has increased up to 25.2%(NREL Best Research-Cell Efficiency Chart, https://www.nrel.gov/pv/cell-efficiency.html, Accessed August 2019). However, they suffer from poor thermal stability due to the volatile A-site organic cations.

Perovskite-based tandem solar cells

The power conversion efficiency for single-junction solar cells is limited by the Shockley-Quiesser limit.An effective approach to realize high efficiency is to develop multi-junction cells.These years have witnessed the rapid development of organic–inorganic perovskite solar cells.The excellent optoelectronic properties and tunable bandgaps of perovskite materials make them potential candidates for developing tandem solar cells,by combining with silicon,Cu(In,Ga)Se_(2)and organic solar cells.In this review,we present the recent progress of perovskite-based tandem solar cells,including perovskite/silicon,perovskite/perovskite,perovskite/Cu(In,Ga)Se_(2),and perovskite/organic cells.Finally,the challenges and opportunities for perovskite-based tandem solar cells are discussed.

钙钛矿叠层太阳电池中电荷传输材料的研究进展

开发钙钛矿叠层太阳电池是一种可以突破单结太阳电池Shockley-Queisser极限的光伏技术.令人鼓舞的是,所有钙钛矿叠层器件,包括钙钛矿/硅、钙钛矿/钙钛矿、钙钛矿/铜铟镓硒和钙钛矿/有机叠层电池,都表现出比相应单结太阳电池更高的效率,显示出巨大的进一步突破的潜力.在叠层器件中,电荷传输材料是钙钛矿子电池的重要组成部分,它直接决定了器件的电荷传输和能量损失.一般来说,高导电性和透光性、良好的能级和化学稳定性是电荷传输材料叠层应用的关键.迄今为止,导电金属氧化物、有机分子、聚合物、富勒烯、自组装材料等各种电荷传输材料已被广泛应用于高效叠层电池.在本文中,我们首先总结了不同类型钙钛矿叠层电池的电荷传输材料的最新进展,详细讨论了材料的电学和光学性质及其对器件性能的影响.在此基础上,我们提出了叠层电池中电荷传输材料进一步发展所面临的挑战和展望.本综述将为不同钙钛矿叠层太阳电池的器件设计提供有效指导.

The integration structure enhances performance of perovskite solar cells

In recent years,all-inorganic perovskite solar cells(PSCs)have attracted tremendous interest due to their excellent thermal stability[1-3].Unlike organic-inorganic halide perovskites,whose organic component is volatile at temperatures higher than 2000C,all-inorganic perovskites can tolerate temperatures over 400℃without deterioration[4].However,the power conversion efficiency(PCE)for all-inorganic PSCs is much lower than that of organic-inorganic halide PSCs mainly due to its wider bandgap,which leads to limited light absorption and low short-circuit current density(Jsc).At present,the most studied all-inorganic perovskites are CsPbI3 and CsPbI2Br.Partly replacing I with Br can decrease the preparation temperature,but the bandgap will increase[5,6].To improve the performance of inorganic PSCs,many researches focused on crystallinity control and interfacial engineering[7-10].Few works were done to broaden the photoresponse to improve Jsc,thus improving the PCE.Developing tandem or integrated solar cells is an effective approach to make full use of sunlight[11,12].For tandem solar cells,the preparation process is very complicated.

Modulating preferred crystal orientation for efficient and stable perovskite solar cells—From progress to perspectives

The perovskite solar cell(PSC)has been recognized as a promising candidate for the next generation of photovoltaics due to its excellent power conversion efficiency(PCE),potential low cost and straightforward solution preparation processes.With efforts around the world,the PCE of PSCs has reached 25.7%.As the perovskite film is the most important part of a PSC,its quality dramatically affects the efficiency and stability of the PSC.Numerous works have focused on controlling crystallization to realize oriented growth of perovskite films.Particularly,considering the photoelectric anisotropy of perovskite materials,it is very meaningful to investigate the relationship between preferred crystal orientation and device efficiency and stability.This review highlights various approaches for realizing preferred crystal orientation of polycrystalline perovskite films,including optimizing the perovskite precursor solution and film annealing process,additive engineering,and interface engineering.Furthermore,the key factors affecting oriented crystal growth are carefully discussed,which provides effective guidance to obtain highly-oriented perovskite films for highly efficient and stable PSCs.

Proton-transfer-induced in situ defect passivation for highly efficient wide-bandgap inverted perovskite solar cells

Wide-bandgap(≥1.68 eV)inverted perovskite solar cells(PSCs)have been recognized as promising top component cells on the commercial crystalline silicon cell to surpass its Shockley-Queisser efficiency limit.However,the power conversion efficiency(PCE)is dramatically limited by the huge open-circuit voltage(V_(OC))loss.Herein,we propose a proton-transfer-induced in situ defect passivation strategy to reduce the nonradiative recombination to minimize the VOC loss.Specifically,a liquid-form neutral amine,3,4,5-trifluorobenzylamine(TFBA)was added into ethyl acetate(EA)as anti-solvent for the film preparation,which induces proton-transfer from the formamidinium(FA)and methylammonium(MA)in the perovskite precursors to the TFBA.The protonated TFBA exhibits a gradient distribution near the surface of the perovskite film,achieving in situ defect passivation.As a result,TFBA-based 1.68 eV-bandgap inverted PSCs afforded a PCE of 20.39%,one of the highest for cells with this bandgap.Meanwhile,due to the strong interaction between TFBA and the perovskite film,the mixed-halide perovskites demonstrate much better photostability.Our findings offer an effective strategy to passivate defects in PSCs.