Evolution of the Electronic Traps in Perovskite Photovoltaics during 1000 h at 85 degrees C

With growing demands on the stability of perovskite photovoltaics against various degradation factors, understanding and controlling the defect characteristics of devices have become the most essential issues to be resolved. In this work, the organometal halide perovskite is modified with a lithium???fluoride ionic passivator that enables highly stable and efficient solar cells with a power-conversion efficiency of over 21%, retaining up to ???90% after 1000 h at 85 ??C. The thermal degradation regressions of the films and devices have been temporally investigated, and the trap density of states has been scrutinized as a function of time. Surprisingly, the electronic traps of the solar cells exhibit exponential relaxations in both the trap densities and energy levels as thermally stressed, and the incorporation of LiF has greatly enhanced this relaxation with the mitigation of the following degradation. It is suggested that LiF not only passivates the initial formation of the traps but also controls their roles and behaviors under the thermal degradation of devices.N

CuCrO2 Nanoparticles Incorporated into PTAA as a Hole Transport Layer for 85 degrees C and Light Stabilities in Perovskite Solar Cells

High-mobility inorganic CuCrO2 nanoparticles are co-utilized with conventional poly(bis(4-phenyl)(2,5,6-trimethylphenyl)amine) (PTAA) as a hole transport layer (HTL) for perovskite solar cells to improve device performance and long-term stability. Even though CuCrO2 nanoparticles can be readily synthesized by hydrothermal reaction, it is difficult to form a uniform HTL with CuCrO2 alone due to the severe agglomeration of nanoparticles. Herein, both CuCrO2 nanoparticles and PTAA are sequentially deposited on perovskite by a simple spin-coating process, forming uniform HTL with excellent coverage. Due to the presence of high-mobility CuCrO2 nanoparticles, CuCrO2/PTAA HTL demonstrates better carrier extraction and transport. A reduction in trap density is also observed by trap-filled limited voltages and capacitance analyses. Incorporation of stable CuCrO2 also contributes to the improved device stability under heat and light. Encapsulated perovskite solar cells with CuCrO2/PTAA HTL retain their efficiency over 90% after similar to 900-h storage in 85 degrees C/85% relative humidity and under continuous 1-sun illumination at maximum-power point

A Cu2O-CuSCN Nanocomposite as a Hole-Transport Material of Perovskite Solar Cells for Enhanced Carrier Transport and Suppressed Interfacial Degradation

Interfacial degradation in perovskite solar cells is a critical issue affecting long-term stability for future commercialization. In particular, a perovskite and an organic hole-transport layer (HTL) react easily when the device is exposed to extreme operating conditions (heat, light, and air). To prevent degradation, an inorganic CuSCN HTL has emerged as an alternative, yet the interfacial reactivity is still not clearly elucidated. Herein, Cu2O and CuSCN are coutilized to form an efficient and stable HTL. While uniform film formation using Cu2O is difficult despite its high mobility, a Cu2O-CuSCN nanocomposite can be excellently synthesized as an effective HTL, exhibiting a power conversion efficiency (PCE) of 19.2% and sustaining its PCE over 90% for 720 h under extreme conditions (85 degrees C/85% of relative humidity, encapsulated). A chemical distribution analysis by secondary-ion mass spectroscopy (SIMS) suggests that a Cu2O nanoparticle layer protects the interface between the perovskite and CuSCN. The optoelectronic properties of the nanocomposite HTL and the improved solar cell performance are correlated with the recombination rate, electronic trap distribution in the band gap, and charge extraction efficiencies.N

Design of SnO2 Electron Transport Layer in Perovskite Solar Cells to Achieve 2000 h Stability Under 1 Sun Illumination and 85 °C

Abstract In order to realize both efficient and stable perovskite solar cells, designing electron transport layer (ETL) is of crucial importance to withstand constant light illumination and thermal stress while maintaining high charge extractability. Herein, commonly used SnO2 nanoparticle‐based ETL for perovskite solar cells is modified by ionic‐salt ammonium chloride (NH4Cl) and tin chloride dihydrate (SnCl2∙2H2O) as additives, which is easily fabricated by simple one‐step spin coating of single precursor solution. With the presence of these dual additives at the ETL, the crystallinity of the upper perovskite layer is clearly enhanced. Defect analyses on the devices suggest that these modifications can effectively passivate trap sites that reside within the ETL and at the perovskite interfaces with the carrier‐transport layers. As a result, the modified SnO2 ETL results in an improvement of device stability under thermal or light stress condition, maintaining over 80% of its initial efficiency after ≈2000 h storage under elevated temperature (85 °C) and after ≈2400 h of operation under 1 sun illumination

Route to Improving Photovoltaics Based on CdSe/CdSe_<i>x</i>Te_1–<i>x</i> Type-II Heterojunction Nanorods: The Effect of Morphology and Cosensitization on Carrier Recombination and Transport

One-dimensionally elongated nanoparticles with type-II staggered band offset are of potential use as light-harvesting materials for photovoltaics, but only a limited attention has been given to elucidate the factors governing the cell performance obtainable from such materials. Herein, we describe a combined strategy to enhance charge collection from CdSe/CdSe_<i>x</i>Te_1–<i>x</i> type-II heterojunction nanorods (HNRs) utilized as light harvesters for sensitized solar cells. By integrating morphology- and composition-tuned type-II HNRs into solar cells, factors that yield interfaces favorable both for the electron injection into TiO₂ and hole transfer to electrolyte are examined. Furthermore, it is shown that a more efficient photovoltaic system results from cosensitization with CdS quantum dots (QDs) predeposited on a TiO₂ scaffold, which improves charge collection from HNRs. Electrochemical impedance spectroscopy (EIS) analysis suggests that such a synergistically enhanced system benefits from the decreased recombination within HNRs and facilitated charge transport through the cosensitized TiO₂ electrode, even with the activation of a recombination path presumably related to the photogenerated holes in CdS QDs