Ionic Liquid Engineering in Perovskite Photovoltaics

Over the past decade,perovskite photovoltaics have approached other currently available technologies and proven to be the most prospective type of solar cells.Although the many-sided research in this very active field has generated consistent results with regard to their undisputed consistently increasing power conversion efficiency,it also produced several rather contradictory opinions.Among other important details,debate surrounding their proneness to surface degradation and poor mechanical robustness,as well as the environmental footprint of this materials class,remains a moot point.The application of ionic liquids appears as one of the potential remedies to some of these challenges due to their high conductivity,the opportunities for chemical"tuning"of the structure,and relatively lower environmental footprint.This article provides an overview,classification,and applications of ionic liquids in perovskite solar cells.We summarize the use and role of ionic liquids as versatile additives,solvents,and modifiers in perovskite precursor solution,in charge transport layer,and in interfacial and stability engineering.Finally,challenges and the future prospects for the design and/or selection of ionic liquids with a specific profile that meets the requirements for next-generation highly efficient and stable perovskite solar cells are proposed.

Achieving Tunable Cold/Warm White‑Light Emission in a Single Perovskite Material with Near‑Unity Photoluminescence Quantum Yield

Single materials that exhibit efficient and stable white-light emission are highly desirable for lighting applications.This paper reports a novel zero-dimensional perovskite,Rb_(4)CdCl_(6):Sn^(2+),Mn^(2+),which demonstrates exceptional white-light properties including adjustable correlated color temperature,high color rendering index of up to 85,and near-unity photoluminescence quantum yield of 99%.Using a co-doping strategy involving Sn^(2+)and Mn^(2+),cyan-orange dual-band emission with complementary spectral ranges is activated by the self-trapped excitons and d-d transitions of the Sn^(2+)and Mn^(2+)centers in the Rb_(4)CdCl_(6)host,respectively.Intriguingly,although Mn^(2+)ions doped in Rb_(4)CdCl_(6)are difficult to excite,efficient Mn^(2+)emission can be realized through an ultra-high-efficient energy transfer between Sn^(2+)and Mn^(2+)via the formation of adjacent exchange-coupled Sn–Mn pairs.Benefiting from this efficient Dexter energy transfer process,the dual emission shares the same optimal excitation wavelengths of the Sn^(2+)centers and suppresses the non-radiative vibration relaxation significantly.Moreover,the relative intensities of the dual-emission components can be modulated flexibly by adjusting the fraction of the Sn^(2+)ions to the Sn–Mn pairs.This co-doping approach involving short-range energy transfer represents a promising avenue for achieving high-quality white light within a single material.

In-depth understanding of ionic liquid assisted perovskite film formation mechanism for two-step perovskite photovoltaics

Ionic liquids(ILs)have been widely applied in the one-step fabrication of perovskite with noticeable enhancement in the device performance.However,in-depth mechanism of ionic-liquid-assisted perovskite film formation is not well understood for also important two-step perovskite fabrication method,with better control of crystallization behavior.In this work,we introduced ionic liquid methylammonium formate(MAFa)into organic salt to produce perovskite film via a two-step method.Systematic investigations on the influence of MAFa on the perovskite thin film formation mechanism were performed.Ionic liquid is shown to assist lowering the perovskite formation enthalpy upon the density functional theory(DFT)calculation,leading to an accelerated crystallization process evidenced by in-situ UV-Vis absorption measurement.A gradient up-down distribution of ionic liquid has been confirmed by timeof-flight SIMS.Importantly,besides the surface passivation,we found the HCOO-can diffuse into the perovskite crystals to fill up the halide vacancies,resulting in significant reduction of trap states.Uniform perovskite films with significantly larger grains and less defect density were prepared with the help of MAFa IL,and the corresponding device efficiency over 23%was obtained by two-step process with remarkably improved stability.This research work provides an efficient strategy to tune the morphology and opto-electronic properties of perovskite materials via ionic-liquid-assisted two-step fabrication method,which is beneficial for upscaling and application of perovskite photovoltaics.

Ionic liquid engineering enabled in-plane orientated 1D perovskite nanorods for efficient mixed-dimensional perovskite photovoltaics

Mixed-dimensional engineering of perovskite material has been demonstrated as a facile and promising strategy to improve both photovoltaic performance and long-term stability of perovskite solar cells(PSCs).In this study,we report an in-plane preferred orientation of 1D perovskite induced by an ionic liquid(IL)of 1-(3-cyanopropyl)-3-methylimidazolium chloride(CPMIMCl)for the first time via sequential deposition approach,leading to a mixed dimensional perovskite thin films.The generated one-dimensional(1D)CPMIMPbI3 with in-plane orientation resides at the grain boundaries of three-dimensional(3D)perovskite can be appreciably observed from the morphology level,leading to creation of high-quality films with large grain size with more efficient defect passivation.Moreover,the dispersion of IL in the bulk phase of perovskite material allows for the formation of 1D perovskite for multiple level passivation to inhibit non-radiative recombination and optimize carrier transport.This IL engineering strategy not only yields a mixed-dimensional perovskite heterostructure with in-plane orientation 1D perovskite nano-rods but also significantly improves the opto-electronic property with suppressed trap states.As a result,the CPMIMCl-treated PSCs show an enhanced photovoltaic performance with a champion power conversion efficiency(PCE)up to 24.13%.More importantly,benefiting from the hydrophobicity of formed 1D perovskite and defects suppression,the corresponding PSC demonstrates an excellent longterm stability and maintain 97.1%of its pristine PCE at 25C under 50%RH condition over 1000 h.This research provides an innovative perspective for employing the low dimensional engineering to optimize the performance and stability of photovoltaic devices.

Efficient energy transfer in organic light-emitting transistor with tunable wavelength

Key challenges in the development of organic light-emitting transistors(OLETs)are blocking both scientific research and practical applications of these devices,e.g.,the absence of high-mobility emissive organic semiconductor materials,low device efficiency,and color tunability.Here,we report a novel device configuration called the energy transfer organic light-emitting transistor(ET-OLET)that is intended to overcome these challenges.An organic fluorescent dye-doped polymethyl methacrylate(PMMA)layer is inserted below the conventional high-mobility organic semiconductor layer in a single-component OLET to separate the functions of the charge transport and light-emitting layers,thus making the challenge to essentially integrate the high mobility and emissive functions within a single organic semiconductor in a conventional OLET or multilayer OLET unnecessary.In this architecture,there is little change in mobility,but the external quantum efficiency(EQE)of the ET-OLET is more than six times that of the conventional OLET because of the efficient Förster resonance energy transfer,which avoids exciton-charge annihilation.In addition,the emission color can be tuned from blue to white to green-yellow using the sourcedrain and gate voltages.The proposed structure is promising for use with electrically pumped organic lasers.

Room-temperature multiple ligands-tailored SnO_(2) quantum dots endow in situ dual-interface binding for upscaling efficient perovskite photovoltaics with high V_(OC)

The benchmark tin oxide(SnO_(2))electron transporting layers(ETLs)have enabled remarkable progress in planar perovskite solar cell(PSCs).However,the energy loss is still a challenge due to the lack of“hidden interface”control.We report a novel ligand-tailored ultrafine SnO_(2) quantum dots(QDs)via a facile rapid room temperature synthesis.Importantly,the ligand-tailored SnO_(2) QDs ETL with multi-functional terminal groups in situ refines the buried interfaces with both the perovskite and transparent electrode via enhanced interface binding and perovskite passivation.These novel ETLs induce synergistic effects of physical and chemical interfacial modulation and preferred perovskite crystallization-directing,delivering reduced interface defects,suppressed non-radiative recombination and elongated charge carrier lifetime.Power conversion efficiency(PCE)of 23.02%(0.04 cm^(2))and 21.6%(0.98 cm^(2),V_(OC) loss:0.336 V)have been achieved for the blade-coated PSCs(1.54 eV E_(g))with our new ETLs,representing a record for SnO_(2) based blade-coated PSCs.Moreover,a substantially enhanced PCE(V_(OC))from 20.4%(1.15 V)to 22.8%(1.24 V,90 mV higher V_(OC),0.04 cm^(2) device)in the blade-coated 1.61 eV PSCs system,via replacing the benchmark commercial colloidal SnO_(2) with our new ETLs.

Recent progress of scalable perovskite solar cells and modules

The rapid development of perovskite solar cells(PSCs)over the past decade makes it the most promising next generation photovoltaic technology.Splendid progress in efficiency and stability has been demonstrated in laboratory level,while endeavours are extremely required to enable successful transfer of the printable PSC technology to industry scale toward commercialization.In this work,recent progresses on upscaling of PSCs are systematically reviewed.Starting with the traditional PSC structure,we have analyzed the specially designed configuration for perovskite solar modules(PSMs).The comprehensive overview and assessment are provided for the technologies engineering in large-scale preparation,including both solution processing and vapor-phase deposition methods.Considering the promoting effect of material engineering to scale up PSMs,the application of additive engineering,solvent engineering and interface engineering on the stability and efficiency of PSMs is systematacially discussed.Moreover,the effect of current packaging technology of PSMs on device lifetime and environmental friendliness is emphasized.At last,we propose the prospects and challenges of PSMs commercialization in the future to meet the requirements for next generation photovoltaic industry.