Improving the long-term stability of perovskite solar cells is critical to the deployment of this technology. Despite the great emphasis laid on stability-related investigations, publications lack consistency in experimental procedures and parameters reported. It is therefore challenging to reproduce and compare results and thereby develop a deep understanding of degradation mechanisms. Here, we report a consensus between researchers in the field on procedures for testing perovskite solar cell stability, which are based on the International Summit on Organic Photovoltaic Stability (ISOS) protocols. We propose additional procedures to account for properties specific to PSCs such as ion redistribution under electric fields, reversible degradation and to distinguish ambient-induced degradation from other stress factors. These protocols are not intended as a replacement of the existing qualification standards, but rather they aim to unify the stability assessment and to understand failure modes. Finally, we identify key procedural information which we suggest reporting in publications to improve reproducibility and enable large data set analysis. Reliability of stability data for perovskite solar cells is undermined by a lack of consistency in the test conditions and reporting. This Consensus Statement outlines practices for testing and reporting stability tailoring ISOS protocols for perovskite devices.

/pdf/consensus-statement-for-stability-assessment-and-reporting-37ng2o1dmx.pdf

Consensus statement for stability assessment and reporting for perovskite photovoltaics based on ISOS procedures

Towards Oxide Electronics: a Roadmap

Polymeric dielectrics play a key role in the realization of flexible organic electronics, especially for the fabrication of scalable device arrays and integrated circuits. Among a wide variety of polymeric dielectric materials, aromatic polyimides (PIs) are flexible, lightweight, and strongly resistant to high-temperature processing and corrosive etchants and, therefore, have become promising candidates as gate dielectrics with good feasibility in manufacturing organic electronic devices. More significantly, the characteristics of PIs can be conveniently modulated by the design of their chemical structures. Herein, from the perspective of structure optimization and interface engineering, a brief overview of recent progress in PI-based dielectrics for organic electronic devices and circuits is provided. Also, an outlook of future research directions and challenges for polyimide dielectric materials is presented.

Recent Progress in Aromatic Polyimide Dielectrics for Organic Electronic Devices and Circuits.

The last decade has witnessed the skyrocketing progress of perovskite solar cells (PSCs) with their current world record energy conversion efficiency reaching over 24%. Nevertheless, the unsatisfactory device stability and current–voltage hysteresis normally observed with most PSCs under operational conditions are the bottlenecks that restrict the application of this photovoltaic technology in practice. It is known that interface properties are at the heart of an electronic device's performance. Understanding the interactions occurring at the interfaces is important to design and develop effective strategies to address these issues associated with PSCs. In this review, we summarize the most recent advancement in understanding the interfaces in PSCs, in particular the interfaces of perovskite/electron transport layer (ETL) and perovskite/hole transport layer (HTL). Our main interest is to provide guidance on the immense complexity of dynamic behaviours of PSCs, particularly concerning the slowest time scale measurements that have a maximum impact on the actual operation of the solar cell. Therefore we address the separation of phenomena such as ion migration, interfacial charge accumulation, and surface electrochemical reactions. We provide an analysis of electrooptical small perturbation methods, including impedance spectroscopy (IS), and a description of negative capacitance, as well as spatially resolved techniques. The impact of different contacts with variable morphology and composition on the perovskite/ETL and perovskite/HTL interface properties reflected by the kinetics of charge transport and chemical reactions is discussed to provide deep insights into the operational mechanism of PSCs. We reach the conclusion that a number of measurements observed in the time frame of 0.1 to 10 s are due to the slow response of the ionic double layer, and we identify the asymmetric surface charge and discharge processes responsible for such kinetic effects. We also suggest the research direction regarding new approaches to understanding interfacial reactions of PSCs to achieve high device performance in the future.

Kinetic and material properties of interfaces governing slow response and long timescale phenomena in perovskite solar cells

The nonradiative recombination of electrons and holes has been identified as the main cause of energy loss in hybrid organic-inorganic perovskite solar cells (PSCs). Sufficient built-in field and defect passivation can facilitate effective separation of electron-hole pairs to address the crucial issues. For the first time, we introduce a homochiral molecular ferroelectric into a PSC to enlarge the built-in electric field of the perovskite film, thereby facilitating effective charge separation and transportation. As a consequence of similarities in ionic structure, the molecular ferroelectric component of the PSC passivates the defects in the active perovskite layers, thereby inducing an approximately eightfold enhancement in photoluminescence intensity and reducing electron trap-state density. The photovoltaic molecular ferroelectric PSCs achieve a power conversion efficiency as high as 21.78 %.

https://onlinelibrary.wiley.com/doi/pdf/10.1002/anie.202012172

Molecular Ferroelectrics‐Driven High‐Performance Perovskite Solar Cells

State-of-the-art halide perovskite solar cells employ semiconductor oxides as electron transport materials. Defects in these oxides, such as oxygen vacancies (Ovac), act as recombination centres and, in air and UV light, reduce the stability of the solar cell. Under the same conditions, the PbZrTiO3 ferroelectric oxide employs Ovac for the creation of defect-dipoles responsible for photo-carrier separation and current transport, evading device degradation. We report the application of PbZrTiO3 as the electron extraction material in triple cation halide perovskite solar cells. The application of a bias voltage (poling) up to 2 V, under UV light, is a critical step to induce charge transport in the ferroelectric oxide. Champion cells result in power conversion efficiencies of ∼11% after poling. Stability analysis, carried out at 1-sun AM 1.5 G, including UV light in air for unencapsulated devices, shows negligible degradation for hours. Our experiments indicate the effect of ferroelectricity, however alternative conducting mechanisms affected by the accumulation of charges or the migration of ions (or the combination of them) cannot be ruled out. Our results demonstrate, for the first time, the application of a ferroelectric oxide as an electron extraction material in efficient and stable PSCs. These findings are also a step forward in the development of next generation ferroelectric oxide-based electronic and optoelectronic devices.

/pdf/pbzrtio3-ferroelectric-oxide-as-an-electron-extraction-34rhw9dl1q.pdf

PbZrTiO3 ferroelectric oxide as an electron extraction material for stable halide perovskite solar cells

This study presents a new self-powered electronic transistor concept "the solar transistor." The transistor effect is enabled by the functional integration of a ferroelectric-oxide thin film and an organic bulk heterojunction. The organic heterojunction efficiently harvests photon energy and splits photogenerated excitons into free electron and holes, and the ferroelectric film acts as a switchable electron transport layer with tuneable conduction band offsets that depend on its polarization state. This results in the device photoconductivity modulation. All this (i.e., carrier extraction and poling) is achieved with only two sandwiched electrodes and therefore, with the role of the gating electrode being taken by light. The two-terminal solar-powered phototransistor (or solaristor) thus has the added advantages of a compact photodiode architecture in addition to the nonvolatile functionality of a ferroelectric memory that is written by voltage and nondestructively read by light.

/pdf/a-solar-transistor-and-photoferroelectric-memory-4lmiz0hmis.pdf

Ian Shirley

Papers

PbZrTiO3 ferroelectric oxide as an electron extraction material for stable halide perovskite solar cells

A Solar Transistor and Photoferroelectric Memory