Solid Additive-Assisted Layer-by-Layer Processing for 19%Efficiency Binary Organic Solar Cells

Morphology is of great significance to the performance of organic solar cells(OSCs),since appropriate morphology could not only promote the exciton dissociation,but also reduce the charge recombination.In this work,we have developed a solid additive-assisted layer-by-layer(SAA-LBL)processing to fabricate high-efficiency OSCs.By adding the solid additive of fatty acid(FA)into polymer donor PM6 solution,controllable pre-phase separation forms between PM6 and FA.This intermixed morphology facilitates the diffusion of acceptor Y6 into the donor PM6 during the LBL processing,due to the good miscibility and fast-solvation of the FA with chloroform solution dripping.Interestingly,this results in the desired morphology with refined phase-separated domain and vertical phase-separation structure to better balance the charge transport/collection and exciton dissociation.Consequently,the binary single junction OSCs based on PM6:Y6 blend reach champion power conversion efficiency(PCE)of 18.16%with SAA-LBL processing,which can be generally applicable to diverse systems,e.g.,the PM6:L8-BO-based devices and thick-film devices.The efficacy of SAA-LBL is confirmed in binary OSCs based on PM6:L8-BO,where record PCEs of 19.02%and 16.44%are realized for devices with 100 and 250 nm active layers,respectively.The work provides a simple but effective way to control the morphology for high-efficiency OSCs and demonstrates the SAA-LBL processing a promising methodology for boosting the industrial manufacturing of OSCs.

Technoeconomically competitive four-terminal perovskite/graphenesilicon tandem solar cells with over 20% efficiency

Perovskite/Silicon(PS) tandem solar cells have attracted much interest over recent years. However, the most popular crystalline silicon solar cells utilized in tandems require complicated fabrication processes mainly including texturization, diffusion, passivation and metallization, which takes up much cost in photovoltaic market. Here, we report a facile graphene/silicon(Gr/Si) solar cell featuring of lowtemperature( 200 °C) processing and an efficiency of 13.56%. For reducing the heat dissipation loss of high energy photon, the perovskite solar cell(PSC) with a wide band gap of 1.76 e V was adopted as the top cell for the tandem. To reduce the loss of parasitic absorption in hole transport layers(HTLs),thickness of Spiro-OMe TAD is re-optimized by compromising the efficiency and the optical transmittance of the devices. As a result, the semitransparent top perovskite solar cell yields a highest efficiency of13.35%. Furthermore, we firstly achieved a low-temperature-processed four-terminal(4-T) perovskite/graphene-silicon(PGS) heterojunction tandem solar cell with the efficiency of 20.37%. The levelized cost of electricity(LCOE) of PGS 4-T modules were estimated to a competitive price, exhibiting much greater potential for practical application compared to that of PS 4-T modules.

Near-infrared non-fused electron acceptors for efficient organic photovoltaics

Developing narrow-bandgap organic semiconductors is important to facilitate the advancement of organic photovoltaics(OPVs). Herein, two near-infrared non-fused ring acceptors(NIR NFRAs), PTBFTT-F and PTBFTT-Cl have been developed with A-π_A-π_D-D-π_D-π_A-A non-fused structures. It is revealed that the introduction of electron deficient π-bridge(π_A) and multiple intramolecular noncovalent interactions effectively retained the structural planarity and intramolecular charge transfer of NFRAs, extending strong NIR photon absorption up to 950 nm. Further, the chlorinated acceptor, with the enlarged π-surface compared to the fluorinated counterpart, promoted not only molecular stacking in solid, but also the desirable photochemical stability in ambient, which are helpful to thereby improve the exciton and charge dynamics for the corresponding OPVs. Overall, this work provides valuable insights into the design of NIR organic semiconductors.

Ion Migration and Accumulation in Halide Perovskite Solar Cells

Comprehensive Summary The halide perovskite semiconductors-based solar cells(PVSCs)show great promise as next-generation renewable energy sources,with the merits of low cost,high performance,good flexibility,etc.A major difference distinguishing the perovskite semiconductors from others lies in their ionic feature.This intrinsic property induces“freely-moving”ions to migrate and accumulate in the perovskite films and devices under different external stresses.As a charge carrier,these processes will strongly couple with the electronic process,and dramatically affect the performance and stability of PVSCs.This review summarizes and discusses the recent progresses and fundamental understandings of ion migration and accumulation behaviors in PVSCs.First,the basic principles of the general ion migration are reviewed.Second,following the fundamental understandings,the critical factors,e.g.,ion migration activation energy,ion density,ion diffusion coefficient,etc.,are extracted to understand the ion migration and accumulation in perovskite film.Third,the principles governing ion accumulation behaviors under different external stresses are discussed.Finally,the effect of ion migration and accumulation on band bending,and device performance is presented.Therefore,we hope this review provides a tutorial and insightful perspective regarding the most prominent ionic feature of perovskite semiconductors and their application for photovoltaics.

A multifunctional and scalable fullerene electron transporting material for efficient inverted perovskite solar cells and modules

The interfacial properties between charge transporting material and perovskite(PVSK)play critical roles in governing the photovoltaic performances of perovskite solar cells(PVSCs).Herein,we develop a multifunctional fulleropyrrolidine(FMG)as an electron transporting material(ETM),which facilitates the construction of efficient and stable inverted PVSCs and modules.It revealed that the facile and scalable FMG possesses not only excellent electron extraction capabilities,but also multi-groups to simultaneously passivate PVSKs via Lewis acid-base and hydrogen bonding interactions.The coating of FMG onto PVSK interestingly yields a dense and interactive layer with the graded ETM-PVSK heterojunction architecture.As a result,FMGbased PVSCs demonstrate a champion efficiency of 23.8%,outperforming 21.0%of PCBM-based devices.FMG could also be utilized to improve photovoltaic performance of large-scale modules.In addition,FMG has successfully elongated the lifetime of the corresponding PVSCs,maintaining 85%of the initial performance after the continuous 60-day one sun equivalent illumination in ambient.

Curing the vulnerable heterointerface via organic-inorganic hybrid hole transporting bilayers for efficient inverted perovskite solar cells

To promote the practices of perovskite photovoltaics,it requires to develop efficient perovskite solar cells(PVSCs)standing long-time operation under the adverse environments.Herein,we demonstrate that the tailor-made conjugated polymers as conductive adhesives stabilized the originally redox-reactive heterointerface between perovskite and metal oxide,facilitating the access of efficient and stable inverted PVSCs.It was revealed that bithiophene and phenyl alternating conjugated polymers with partial glycol chains atop of the metal oxide layer has resulted in effective organic-inorganic hybrid hole transporting bilayers,which allow maintaining efficient hole extraction and transport,meanwhile preventing halide migration to directly contact with the nickel oxide(NiO_(x))layer.As a result,the corresponding inverted PVSCs with the organic-inorganic hole transporting bilayers have achieved an excellent power conversion efficiency of 23.22%,outperforming 20.65% of bare NiO_(x)-based devices.Moreover,the encapsulated PVSCs with organic-inorganic bilayers exhibited the excellent photostability with 91% of the initial efficiency after 1000-h one-sun equivalent illumination in ambient conditions.Overall,this work provides new insights into stabilizing the vulnerable heterointerface for perovskite solar cells.

Black phosphorus nanoflakes as morphology modifier for efficient fullerene-free organic solar cells with high fill-factor and better morphological stability

Morphology of the donor:acceptor blend plays a critical role in the photovoltaic performance of the organic solar cells (OSCs).Herein,liquid-phase-exfoliated black phosphorus nanoflakes (BPNFs),for their outstanding electronic property and good compatibility to solution process,were applied to fullerene-free OSCs as morphology modifier.Revealed by X-ray scattering measurements,the PTB7-Th:IEICO-4F blends incorporated with BPNFs exhibit more ordered π-π stacking and promoted domain purity,contributing to lower charge transport resistance and suppressed charge recombination within the bulk heterojunction (BHJ).As a result,a high fill factor (FF) of 0.73 and a best power conversion efficiency (PCE) of 12.2% were obtained for fullerene-free OSCs based on PTB7-Th:IEICO-4F blends incorporating with BPNFs,which is among the highest FF of the as-cast fullerene-free OSCs with PCE over 12%.More importantly,the embedded BPNFs help to improve the morphological stability of the devices probably by retarding the phase mixing in the BHJ during the aging period.Besides,analogous enhancements were observed in another fullerene-free OSCs based on PBDB-T:ITIC.In a word,this work provides a new strategy of using two-dimentional nanoflakes as facile and universal morphology modifier for efficient fullerene-free OSCs.

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.

Recent advances in plasmonic organic photovoltaics

Light trapping based on the localized surface-plasmon resonance(LSPR)effect of metallic nanostructures is a promising strategy to improve the device performance of organic solar cells(OSCs).We review recent advances in plasmonic-enhanced OPVs with solution-processed metallic nanoparticles(NPs).The different types of metallic NPs(sizes,shapes,and hybrids),incorporation positions,and NPs with tunable resonance wavelengths toward broadband enhancement are systematically summarized to give a guideline for the realization of highly efficient plasmonic photovoltaics.

Electron-deficient core fused-ring based non-fullerene acceptor enables over 15% efficiency in single junction organic solar cells

Organic solar cells(OSCs)are promising to access flexible,light weight and semi-transparent photovoltaic devices by low-cost solution fabrication.Recently,the fused-ring nonfullerene acceptors play an important role in promoting the research progress of the OSCs.The power conversion efficiencies(PCEs)have been rapidly boosted to over 14%in single junction OSCs with the development of new nonfullerene acceptors and the related devices[1-3].Although the PCEs of OSCs are still inferior to their inorganic counterparts,further improvement of the PCEs could be expected by the development of new photovoltaic materials.

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.

Sn-Pb Binary Perovskite Films with High Crystalline Quality for High Performance Solar Cells

As an environmentally friendly perovskite material with low bandgap,Tin (Sn)-based perovskite has drawn much attention.A simple and effective method for fabricating high-quality Sn-Pb binary perovskite film is highly desired.Here,with methylammonium chloride (MACI) post-treatment to assist vertical recrystallization,we fabricated high quality FA0.75Cs0.25Pb0sSn0.5l3 perovskite film via one-step processing method.This recrystallization method was first used in Sn-based perovskite.The obtained film consists of vertically aligned grains with high crystallinity,which contributes to a power conversion efficiency (PCE) of 14.03% in corresponding perovskite solar cell (PVSC).The cells maintained 80% of their initial PCEs after being stored for 30 d in glove-box.This simple,effective method provides an easy way to fabricate high performance Sn-Pb binary PVSC.

Highly efficient and thermal stable guanidinium-based two-dimensional perovskite solar cells via partial substitution with hydrophobic ammonium

Layered two-dimensional(2D)perovskite solar cells(PVSCs)with a chemical formula of C(NH2)3(CH3NH3)3Pb3I10(n=3)have been fabricated through additive engineering,wherein stoichiometrically equivalent guanidinium(GA+)and methylammonium(MA+)serve as spacer cations.The crystallinity of the perovskite films is dramatically enhanced with proper amount of methylammonium thiocyanate(MASCN)added into the precursor solution.In addition,we substitute a small amount of MA+with hydrophobic phenylethylammonium(PEA+),which can passivate trap states of the perovskite films.As a result,the open circuit voltage increases to 1.1 V and the best power conversion efficiency(PCE)of 10.12%is yielded.Furthermore,superior thermal stability and balanced moisture stability of the PEA-substituted GA-based PVSCs are demonstrated,compared to the popular 3D MAPbI3and 2D PEA-based PVSCs.They retain approximately 80%of the original PCE after 30 d at 20%relative humidity(RH),and 50%of the original PCE after 3200 min at 85°C without any encapsulation.This work suggests a new route to achieve both heat and humidity stable PVSCs by simply mixing different spacer cations.

Inverted Perovskite Solar Cells Based on Small Molecular Hole Transport Material C8-Dioctylbenzothienobenzothiophene

Summary of main observation and conclusion The small organic molecular Dioctylbenzothienobenzothiophene(C8-BTBT)has been explored as hole transport material(HTM)to replace PEDOT:PSS in inverted perovskite solar cells(PVSCs).MAPbl3 perovskite films depositd onto C8-BTBT are smooth and uniform,with negligible residual of Pbl2 and large grain size even larger than 1μm.Our champion C8-BTBT based devices reached a high power conversion efficiency(PCE)of 15.46%with marginal hysteresis,much higher than that of 11.50%achieved using PEDOT:PSS.Besides,devices adopting C8-BTBT as substrate show superior stability compared with the PEDOT:PSS based devices when stored under ambient conditions with a relative humidity of(25+5)%.

Polypropylene Glycol-Modified Anode Interface for High-Performance Perovskite Solar Cells

The surface properties and chemical interactions are critical for perovskite solar cells(PVSCs).In this work,we show that the polypropylene glycol(PPG)can simultaneously passivate the NiOx surface and grain boundaries of perovskite films,allowing more efficient charge transfer at the anode interface and reducing the recombination of PVSCs.As a result,the open-circuit voltage(Voc)of MAPbI3 based inverted PVSCs increases from 1.087 V to 1.127 V,and the short-circuit current density(Jsc)is increased from 20.87 mA·cm^(–2) to 22.32 mA·cm^(–2),thereby realizing the improvement of the device power conversion efficiency(PCE)from 18.34%to 20.12%.Moreover,the steady-state output of the PVSCs is remarkably improved by incorporating PPG.Further analysis of surface properties suggests that part of the PPG at the interface can permeate into the precursor solution with the help of DMF solvent and remain in the perovskite layer to form a concentration gradient.The ether bond of PPG and the uncoordinated Pb2+in the perovskite are coordinated to achieve passivation effects and improve device performance.

A non-fullerene acceptor enables efficient P3HT-based organic solar cells with small voltage loss and thickness insensitivity

Poly(3-hexylthiophene)(P3HT) is a low-cost polymer donor for organic solar cells (OSCs). However, the P3HT-based OSCs usually give low power conversion efficiencies (PCEs) due to the wide bandgap and the high-lying energy levels of P3HT. To solve this problem, in this work, we design and synthesize a new A-D-A type non-fullerene acceptor, DFPCBR, which owns an electron-donating (D) core constructed by linking a 2,5-difluorobenzene ring with two cyclopentadithiophene moieties, and two electron-accepting (A) end-groups of benzo[c][1,2,5]thiadiazole connected with 3-ethyl-2-thioxothiazolidin-4-one. Because of the strong electron-donating ability and large conjugation effect of D core, DFPCBR shows appropriate energy levels and a narrow bandgap matching well with those of P3HT. Therefore, with P3HT as the donor and DFPCBR as the acceptor, the OSCs possess broad absorption range from 350 nm to 780 nm and the reduced energy loss (Eloss) of 0.79 eV (compared with ~1.40 eV for the P3HT:PC61BM device), providing a good PCE of 5.34% with a high open-circuit voltage (VOC) of 0.80 V. Besides, we observe that the photovoltaic performances of these devices are insensitive to the thickness of the active layers:even if the active layer is as thick as 320 nm,~80%of the best PCE is maintained, which is rarely reported for fullerene-free P3HT-based OSCs, suggesting that DFPCBR has the potential application in commercial OSCs in the future.

Multifunctional semitransparent organic solar cells with excellent infrared photon rejection

Semitransparent organic solar cells(ST-OSCs)have the potentials to open promising applications that differ from those of conventional inorganic ones,such as see-through power windows with both energy generation and heat insulation functions.However,to achieve so,there remain significant challenges,especially for balancing critical parameters,such as power conversion efficiency(PCE),average visible transparency(AVT)and low energy infrared photon radiation rejection(IRR)to realize the full potentials of ST-OSCs.Herein,we demonstrate the new design of ST-OSCs through the rational integration of organic materials,transparent electrode and infrared photon reflector in one device.With the assistance of optical simulation,new ST-OSCs with precise layout exhibit state-of-art performance,with near 30%AVT and PCE of 7.3%,as well as an excellent IRR of over 93%(780-2500 nm),representing one of best multifunctional ST-OSCs with promising perspective for window application.

Design of Non-fused Ring Acceptors toward High-Performance,Stable,and Low-Cost Organic Photovoltaics

Toward future commercial applications of organic solar cells(OSCs),organic photovoltaic materials that enable high efficiency,excellent stability,and low cost should be developed.Fused-ring electron acceptors(FREAs)have declared that OSCs are capable of showing efficiencies over 19%,whereas stability and cost are not solved yet.As the counterparts of FREAs,non-fused ring electron acceptors(NFREAs)are more flexible in molecular design.They have better stability because of the reduction of intramolecular tension via breaking fused backbone and have more advantages in cost with the reduction of synthetic complexity.However,the challenge for NFREAs is the relatively lower efficiencies(around 15%at current stage),which require better molecular designs for addressing the issues of conformational unicity and effective molecular packing.In this Account,we comprehensively summarize works about NFREAs carried out in our group from three main frameworks,including molecular design and efficiency optimization,material cost,and stability.First,in the part of molecular design and efficiency optimization,the existing rotatable single bond in NFREAs will bring the problem of conformational uncertainty,but it can be solved through proper molecular design,which also regulates the energy levels,light absorption range,and the packing mode of the molecule for obtaining higher performance.Thus,in this part,we discuss the evolution of NFREAs in three aspects,including molecular skeleton optimization,terminal modification,and side chain engineering.Many strategies are used in the design of a molecular skeleton,such as utilizing the quinoid effect,introducing functional groups with the electron push−pulling effect,and using multiple conformational lock.Furthermore,simplifying the skeleton is also the preferred development tendency.As for the terminal,the main modification strategy is adjusting the conjugation length and halogen atoms.What is more,by adjusting the side chain to induce appropriate steric hindrance,we can fix the orientation of molecules,thus regulating molecular packing modes.Second,regarding material cost,we compare the synthesis complexities between state-of-the-art FREAs and NFREAs.Because the synthesis processes of NFREAs reduce the complex cyclization reactions,the synthesis routes are greatly simplified,and the molecule can be obtained through three minimal steps.Third,regarding stability,we analyze the workable strategies used in NFREAs from the views of intrinsic material stability,photostability,and thermal stability.Finally,we conclude the challenges that should be conquered for NFREAs and propose perspectives that could be performed for NFREAs,with the hope of pushing the development of OSCs toward high performance,stability,and low cost.

Active-layer evolution and （CH3NH3）3Bi2l9-based solar substrate efficiency improvement of cell on TiO2-deposited ITO

We systematically investigated the development of film morphology and crystallinity of methyl-ammonium bismuth （Ⅲ） iodide （MA3Bi2I9） through one- step spin-coating on TiO2-deposited indium tin oxide （ITO）/glass. The precursor solution concentration and substrate structure have been demonstrated to be critically important in the active-layer evolution of the MA3Bi2I9-based solar cell. This work successfully improved the cell efficiency to 0.42% （average： 0.38%） with the mesoscopic architecture of ITO/compact-TiOdmesoscopic-TiO2 （meso-TiO2）/ MA3Bi2I9/2,2＇,7,7＇-tetrakis（N,N-di-4-methoxyphenylamino）-9,9＇spiro-bifluorene （spiro-MeOTAD）/MoO3/Ag under a precursor concentration of 0.45 M, which provided the probability of further improving the efficiency of the BiB＋-based lead-free organic-inorganic hybrid solar cells.

A-D-A small molecule donors based on pyrene and diketopyrrolopyrrole for organic solar cells

Three new electron donating small molecules(SMs),Pyr(EH-DPP)_2,Pyr(HD-DPP)_2 and PyrA(EH-DPP)_2,are designed and synthesized through coupling electron rich pyrene core with electron deficient diketopyrrolopyrrole(DPP) terminals,of which the derived organic solar cells(OSCs) exhibit interesting structure-performance correlation.It shows that the tune of their solubilizing side chains and π-bridge for the acceptor-donor-acceptor(A-D-A) SMs can significantly alter the resultant short-circuit current density and power conversion efficiency(PCE) in OSCs.The Pyr(EH-DPP)_2 with short side chains displays broader absorption and higher hole mobility than the Pyr(HD-DPP)_2 with long side chains.Although showing planar structure,the acetylene bridge-incorporated PyrA(EH-DPP)_2 adapts an undesired edge-on packing and strong aggregation in film,leading to non-ideal morphology and poor miscibility with fullerene acceptors.As a result,the PCE of the solar cell based on Pyr(EH-DPP)_2 is several times higher than those based on Pyr(HD-DPP)_2 and PyrA(EH-DPP)_2,indicating the A-D-A combination of polyaromatics with DPP would be the promising skeleton for developing photovoltaic semiconductors.