4‑Terminal Inorganic Perovskite/Organic Tandem Solar Cells Offer 22%Efficiency

After fast developing of single-junction perovskite solar cells and organic solar cells in the past 10 years,it is becoming harder and harder to improve their power conversion efficiencies.Tandem solar cells are receiving more and more attention because they have much higher theoretical efficiency than single-junction solar cells.Good device performance has been achieved for perovskite/silicon and perovskite/perovskite tandem solar cells,including 2-terminal and 4-terminal structures.However,very few studies have been done about 4-terminal inorganic perovskite/organic tandem solar cells.In this work,semi-transparent inorganic perovskite solar cells and organic solar cells are used to fabricate 4-terminal inorganic perovskite/organic tandem solar cells,achieving a power conversion efficiency of 21.25%for the tandem cells with spin-coated perovskite layer.By using drop-coating instead of spin-coating to make the inorganic perovskite films,4-terminal tandem cells with an efficiency of 22.34%are made.The efficiency is higher than the reported 2-terminal and 4-terminal inorganic perovskite/organic tandem solar cells.In addition,equivalent 2-terminal tandem solar cells were fabricated by connecting the sub-cells in series.The stability of organic solar cells under continuous illumination is improved by using semi-transparent perovskite solar cells as filter.

A chlorinated copolymer donor demonstrates a 18.13% power conversion efficiency

The rapid development of low-bandgap(LBG)nonfullerene acceptors and wide-bandgap(WBG)copolymer donors in recent years has boosted the power conversion efficiency(PCE)of organic solar cells(OSCs)to the 18%level[1−21].The commercialization of OSCs is highly expected.However,critical issues like the cost and the stability also determine whether OSCs can enter the market or not[22].

Defect passivation by nontoxic biomaterial yields 21% efficiency perovskite solar cells

Defect passivation is one of the most important strategies to boost both the efficiency and stability of perovskite solar cells(PSCs).Here,nontoxic and sustainable forest-based biomaterial,betulin,is first introduced into perovskites.The experiments and calculations reveal that betulin can effectively passivate the uncoordinated lead ions in perovskites via sharing the lone pair electrons of hydroxyl group,promoting charge transport.As a result,the power conversion efficiencies of the p-i-n planar PSCs remarkably increase from 19.14%to 21.15%,with the improvement of other parameters.The hydrogen bonds of betulin lock methylamine and halogen ions along the grain boundaries and on the film surface and thus suppress ion migration,further stabilizing perovskite crystal structures.These positive effects enable the PSCs to maintain 90%of the initial efficiency after 30 days in ambient air with 60%±5%relative humidity,75%after 300 h aging at 85℃,and 55%after 250 h light soaking,respectively.This work opens a new pathway for using nontoxic and low-cost biomaterials from forest to make highly efficient and stable PSCs.

Hollow Bio-derived Polymer Nanospheres with Ordered Mesopores for Sodium-Ion Battery

Bio-inspired hierarchical self-assembly provides elegant and powerful bottom-up strategies for the creation of complex materials.However,the current self-assembly approaches for natural bio-compounds often result in materials with limited diversity and complexity in architecture as well as microstructure.Here,we develop a novel coordination polymerization-driven hierarchical assembly of micelle strategy,using phytic acid-based natural compounds as an example,for the spatially controlled fabrication of metal coordination bio-derived polymers.The resultant ferric phytate polymer nanospheres feature hollow architecture,ordered meso-channels of^12 nm,high surface area of 401 m2 g−1,and large pore volume of 0.53 cm3 g−1.As an advanced anode material,this bio-derivative polymer delivers a remarkable reversible capacity of 540 mAh g−1 at 50 mA g−1,good rate capability,and cycling stability for sodium-ion batteries.This study holds great potential of the design of new complex bio-materials with supramolecular chemistry.

Surface Passivation and Energetic Modification Suppress Nonradiative Recombination in Perovskite Solar Cells

Surface passivation via post-treatment is an important strategy for improving power conversion efficiency and operational stability of perovskite solar cells.However,so far the interaction mechanisms between passivating additive and perovskite are not well understood.Here,we report the atomic-scale interaction of surface passivating additive 2,2-difluoroethylammonium bromine(2FEABr)on the MAPbI_(3).It is found that the bulky 2FEA+cations tend to distribute at film surface,while the Br−anions diffuse from surface into bulk.A combination of 19F,207Pb,and 2H solid-state NMR further reveal the Br−anions’partial substitution for the I−sites,the restricted motion of partial MA+cations,and the firmed perovskite lattices,which would improve charge transport and stability of the perovskite films.Optical spectroscopy and ultraviolet photoelectron spectroscopy demonstrate that the 2FEABr induced surface passivation and energetic modification suppress the nonradiative recombination loss.These findings enable the efficiency of the p-i-n structured PSC significantly increasing from 19.44 to 21.06%,accompanied by excellent stability.Our work further establishes more knowledge link between passivating additive and PSC performance.

Low-Temperature Aging Provides 22% E cient Bromine-Free and Passivation Layer-Free Planar Perovskite Solar Cells

Previous reports of formamidinium/methylamine(FAMA)-mixed halide perovskite solar cells have focused mainly on controlling the morphology of the perovskite film and its interface—for example,through the inclusion of bromine and surface passivation.In this paper,we describe a new processing pathway for the growth of a high-quality bromine-free FAMAPbI3 halide perovskites via the control of intermediate phase.Through low-temperature aging growth(LTAG)of a freshly deposited perovskite film,α-phase perovskites can be seeded in the intermediate phase and,at the same time,prevent beta-phase perovskite to nucleate.After postannealing,large grain-size perovskites with significantly reduced PbI2 presence on the surface can be obtained,thereby eliminating the need of additional surface passivation step.Our pristine LTAG-treated solar cells could provide PCEs of greater than 22%without elaborate use of bromine or an additional passivation layer.More importantly,when using this LTAG process,the growth of the pure alpha-phase FAMAPbI3 was highly reproducible.

Investigating the reason for high FF from ternary organic solar cells

Organic solar cells(OSCs)have attracted huge attention because of their unique merits[1−3].In last few years,thanks to the design of new materials and device engineering,the power conversion efficiencies(PCEs)of OSCs have surpassed 18%[4−8].The PM6:Y6 cells are efficient binary cells,offering high PCEs over 16%[9−11].The high performance originates from the efficient free charge generation and the ground state dipole field at the donor-acceptor interface that promotes the exciton dissociation[12].

Perovskite films with gradient bandgap for self-powered multiband photodetectors and spectrometers

Bandgap-graded materials present varying spectral responses at different positions,making them possible to be used as an alternative to photoactive materials array in multi-spectral responsive devices,thus miniaturizing the apparatus.However,the preparation of bandgap-graded materials usually requires complicated deposition process.Here we report a facile lowtemperature solution process to make films with lateral bandgap gradients,which form spontaneously via self-spreading and interdiffusion of solutions.We show lead halide perovskite films with MAPbCl_(3)-MAPbBr_(3)and MAPbBr_(3)-MAPbI_(3)gradients,which exhibit light absorption onsets ranging from 410 to 781 nm.The bandgap-graded films were used to make self-powered multiband photodetectors,which show different spectral responses at different positions without applying bias voltage.Furthermore,self-powered spectrometers were made by using the multiband photodetectors.

Multifunctional anchoring of O-ligands for high-performance and stable inverted perovskite solar cells

Functional additives have recently been regarded as emerging candidates to improve the performance and stability of perovskite solar cells(PSCs).Herein,nicotinamide(N),2-chloronicotinamide(2Cl),and 6-chloronicotinamide(6Cl)were employed as O-ligands to facilitate the deposition of MAPbI_(3)(MA=methylammonium)and MA-free FA_(0.88)Cs_(0.12)PbI_(2.64)Br_(0.36)(FA=formamidinium)perovskite films by multifunctional anchoring.By density functional theory(DFT)calculations and ultraviolet photoelectron spectroscopy(UPS)measurements,it is identified that the highest occupied molecular orbital(HOMO)level for additive modified MAPbI_(3)perovskite could reduce the voltage deficit for hole extraction.Moreover,due to the most favorable charge distribution and significant improvements in charge mobility and defect passivation,the power conversion efficiency(PCE)of 2Cl-MAPbI_(3)PSCs was significantly improved from 19.32%to 21.12%.More importantly,the two-dimensional grazing-incidence wide-angle X-ray scattering(GIWAXS)analysis showed that PbI_(2) defects were effectively suppressed and femtosecond transient absorption(TA)spectroscopy demonstrated that the trap-assisted recombination at grain boundaries was effectively inhibited in the 2Cl-MA-free film.As a result,the thermally stable 2Cl-MA-free PSCs achieved a remarkable PCE of 23.13%with an open-circuit voltage(V_(oc))of 1.164 V and an ultrahigh fill factor(FF)of 85.7%.Our work offers a practical strategy for further commercializing stable and efficient PSCs.

Organic Semiconductor Interfaces and Their Effects in Organic Solar Cells

Energy levels and energy level alignment at interfaces play a decisive role in designing efficient and stable organic solar cells(OSCs).In this review two usually used technologies in organic photovoltaic communities for measuring energy levels of organic semiconductors,photoelectron spectroscopy and electrochemical methods,are introduced,and the relationships between the values obtained from the corresponding techniques are compared.The energy level and energy level alignment across the interfaces involved in solution processed organic photovoltaics are described,and the corresponding integer charge transfer model for predicting and explaining energy level alignment is presented.The effects of the interface properties in designing efficient binary and ternary OSCs were discussed.The effects of environmental factors mainly including water vapor,oxygen gas and thermal annealing on energy levels and energy level alignment involved in photoactive layers,and the subsequent effects on the corresponding OSC properties are given.

Over 16% efficiency from thick-film organic solar cells

近年来有机太阳电池效率突飞猛进,单结电池效率已经突破18%,然而这些高效率电池的活性层厚度通常只有100 nm左右,随着厚度增加,电池效率下降明显.为了实现有机太阳电池的产业化,发展对厚度不敏感,且可适用于卷对卷印刷制备的高性能厚膜电池势在必行.本文通过在D18:Y6二元活性层中加入少量富勒烯受体PC61BM,使得电池对厚度的敏感性显著降低. PC61BM的加入使厚膜活性层的电子和空穴迁移率明显提高,载流子传输更加平衡,并且显著降低了陷阱辅助复合.D18:Y6:PC61BM(1:1.6:0.2)三元电池在活性层厚度超过300 nm时,还能保持16%以上的效率,是目前性能最优异的厚膜有机太阳电池之一.

Recent progress in organic solar cells(PartⅠmaterial science)

During past several years,the photovoltaic performances of organic solar cells(OSCs)have achieved rapid progress with power conversion efficiencies(PCEs)over 18%,demonstrating a great practical application prospect.The development of material science including conjugated polymer donors,oligomer-like organic molecule donors,fused and nonfused ring acceptors,polymer acceptors,single-component organic solar cells and water/alcohol soluble interface materials are the key research topics in OSC field.Herein,the recent progress of these aspects is systematically summarized.Meanwhile,the current problems and future development are also discussed.

Fused-ring bislactone building blocks for polymer donors

The past 5 years have witnessed the rapid development of organic solar cells based on nonfullerene acceptors(NFAs)[1-26].The state-of-the-art NFA-based single-junction and tandem solar cells afforded 18.22%(certified 17.6%)and 17.36%(certified 17.29%)power conversion efficiencies(PCEs),respectively[27,28].Wide-bandgap(WBG)polymer donors are ideal partners for NFAs.They present complementary absorption with that of low-bandgap NFAs and deep the highest occupied molecular orbital(HOMO)levels.Therefore,solar cells based on a WBG polymer and a NFA can generate high short-circuit current density(Jsc)and open-circuit voltage(Voc)[29].Meanwhile,some WBG polymers show high crystallinity and mobility,gifting the solar cells high fill factors(FF)[30].Recently,our group first reported efficient WBG D-A copolymer donors based on fused-ring aromatic lactone(FRAL)acceptor units.

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.

Recent progress in organic solar cells(PartⅡdevice engineering)

1 Introduction Organic solar cells(OSCs)belong to a multidisciplinary field composed of chemistry,materials science,physics,engineering,etc.For a better reviewing of this field,we briefly divide the research field of OSCs into two parts:material science and device engineering.In our previous review,the material science part of OSCs,including conjugated polymer donors and acceptors,small molecular donors and acceptors.

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.