Review on Chemical Stability of Lead Halide Perovskite Solar Cells

Lead halide perovskite solar cells(PSCs) have become a promising next-generation photovoltaic technology due to their skyrocketed power conversion efficiency. However, the device stability issues may restrict their commercial applications, which are dominated by various chemical reactions of perovskite layers. Hence, a comprehensive illustration on the stability of perovskite films in PSCs is urgently needed. In this review article, chemical reactions of perovskite films under different environmental conditions(e.g., moisture,oxygen, light) and with charge transfer materials and metal electrodes are systematically elucidated. Effective strategies for suppressing the degradation reactions of perovskites, such as buffer layer introduction and additives engineering,are specified. Finally, conclusions and outlooks for this field are proposed. The comprehensive review will provide a guideline on the material engineering and device design for PSCs.

Air-Stable,Eco-Friendly RRAMs Based on Lead-Free Cs_(3)Bi_(2)Br_(9)Perovskite Quantum Dots for High-Performance Information Storage

Development of lead-free halide perovskites that are innocuous and stable has become an attractive trend in resistive random access memory(RRAM)fields.However,their inferior memory properties compared with the lead-based analogs hinder their commercialization.Herein,the lead-free Cs_(3)Bi_(2)Br_(9)perovskite quantum dot(PQD)-based RRAMs are reported with outstanding memory performance,where Cs_(3)Bi_(2)Br_(9)quantum dots(QDs)are synthesized via a modified ligand-assisted recrystallization process.This is the first report of applying Cs_(3)Bi_(2)Br_(9)QDs as the switching layer for RRAM device.The Cs_(3)Bi_(2)Br_(9)QD device demonstrates nonvolatile resistive switching(RS)effect with large ON/OFF ratio of 105,low set voltage of-0.45 V,as well as good reliability,reproducibility,and flexibility.Concurrently,the device exhibits the notable tolerance toward moisture,heat and light illumination,and long-term stability of 200 days.More impressively,the device shows the reliable light-modulated RS behavior,and therefrom the logic gate operations including"AND"and"OR"are implemented,foreboding its prospect in logic circuits integrated with storage and computation.Such multifunctionality of device could be derived from the unique 2D layered crystal structure,small particle size,quantum confinement effect,and photoresponse of Cs_(3)Bi_(2)Br_(9)QDs.This work provides the strategy toward the high-performance RRAMs based on stable and eco-friendly perovskites for future applications.

An Efficient Trap Passivator for Perovskite Solar Cells:Poly(propylene glycol)bis(2‑aminopropyl ether)

Perovskite solar cells(PSCs)are regarded as promising candidates for future renewable energy production.High-density defects in the perovskite films,however,lead to unsatisfactory device performances.Here,poly(propylene glycol)bis(2-aminopropyl ether)(PEA)additive is utilized to passivate the trap states in perovskite.The PEA molecules chemically interact with lead ions in perovskite,considerably passivate surface and bulk defects,which is in favor of charge transfer and extraction.Furthermore,the PEA additive can efficiently block moisture and oxygen to prolong the device lifetime.As a result,PEA-treated MAPbI3(MA:CH3NH3)solar cells show increased power conversion efficiency(PCE)(from 17.18 to 18.87%)and good longterm stability.When PEA is introduced to(FAPbI3)1-x(MAPbBr3)x(FA:HC(NH2)2)solar cells,the PCE is enhanced from 19.66 to 21.60%.For both perovskites,their severe device hysteresis is efficiently relieved by PEA.

Manipulating Crystal Growth and Secondary Phase PbI_(2)to Enable Efficient and Stable Perovskite Solar Cells with Natural Additives

In perovskite solar cells(PSCs),the inherent defects of perovskite film and the random distribution of excess lead iodide(PbI_(2))prevent the improvement of efficiency and stability.Herein,natural cellulose is used as the raw material to design a series of cellulose derivatives for perovskite crystallization engineering.The cationic cellulose derivative C-Im-CN with cyano-imidazolium(Im-CN)cation and chloride anion prominently promotes the crystallization process,grain growth,and directional orientation of perovskite.Meanwhile,excess PbI_(2)is transferred to the surface of perovskite grains or formed plate-like crystallites in local domains.These effects result in suppressing defect formation,decreasing grain boundaries,enhancing carrier extraction,inhibiting non-radiative recombination,and dramatically prolonging carrier lifetimes.Thus,the PSCs exhibit a high power conversion efficiency of 24.71%.Moreover,C-Im-CN has multiple interaction sites and polymer skeleton,so the unencapsulated PSCs maintain above 91.3%of their initial efficiencies after 3000 h of continuous operation in a conventional air atmosphere and have good stability under high humidity conditions.The utilization of biopolymers with excellent structure-designability to manage the perovskite opens a state-of-the-art avenue for manufacturing and improving PSCs.

Thermostable single-junction organic solar cells with a power conversion efficiency of 14.62%

Organic solar cells(OSCs)have drawn substantial attention in recent two decades due to their features of solution processability,low cost,and light weight[1].The active layer of OSCs is usually composed of an electron donor(D)and an electron acceptor(A).The D/A system can form interpenetrated nanoscale network,which allows efficient exciton dissociation and hence charge carrier generation.However,the efficiency of such binary OSCs is gen-

All-solution-processed PIN architecture for ultra-sensitive and ultra-flexible organic thin film photodetectors

An ideal organic thin film photodetectors(OTFPs) should adopt a hierarchical, multilayer p-type/blend-type/n-type(PIN) structure,with each layer having a specific purpose which could greatly improve the exciton dissociation while guarantee efficient charge transport. However, for the traditional layer-by-layer solution fabrication procedure, the solvent used can induce organic material mixing and molecular disordering between each layer. Hence, such architecture for OTFPs can now only be formed via thermal evaporation. In this paper, a contact-film-transfer method is demonstrated to all-solution processing organic PIN OTFPs on flexible substrates. The fabricated PIN OTFPs exhibit high photoresponse and high stability under continuous mechanical bending. Hence,the method we described here should represent an important step in the development of OTFPs in the future.