Dissipation of Charge Accumulation and Suppression of Phase Segregation in Mixed Halide Perovskite Solar Cells via Nanoribbons

Abstract

Mixed halide hybrid perovskite compounds such as MAPbI1.5Br1.5 are among highly acclaimed absorber materials for solar cells due to their easy tunability of band gap. These compounds are intrinsically unstable and often demix into separate phases upon white light illumination, and this undesired process commonly known as photoinduced phase segregation presently impedes the development of mixed halide perovskite (MHP)-formulated solar devices. Understanding the pathways that lead to such phase segregation and controlling them are the key to solve their device instability problems. The miscibility gap that I/Br possesses at room temperature easily allows the separation of the mixed phase of MAPbI1.5Br1.5 into two phases as MAPbBr3 and MaPbI3 on irradiation, which leads to a continuous decrease in V oc in these devices. The low-lying valence band (VB) of the segregated iodine-rich phase facilitates trapping of holes, leading to migration of I– ions toward grain boundaries. Here, we investigate the effects of TiO2-intercalated graphene nanoribbons (GNRs) to hinder the migration and accumulation of I– at grain boundaries. It is found that the remarkably low charge resistance and low electron impedance of the modified electron transport layer (ETL), along with a reduced polaron-induced strain gradient in MHP due to GNRs facilitate against phase segregation, hole accumulation, and carrier recombination. This enables the device to retain its V oc unlike in devices without GNR wherein V oc decreases to zero in less than 60 min of illumination. Using conductive atomic force microscopy (AFM) studies, we reveal the electrical conductivity of TiO2 and TiO2-GNR films. We conclude by positing that TiO2-GNR with improved charge transport properties reduces electric field-induced halide ion migration that may give rise to a decrease in V oc upon continuous light illumination.

Cationic and Anionic Vacancy Healing for Suppressed Halide Exchange and Phase Segregation in Perovskite Solar Cells

“…All-inorganic WBG cells, similar to their organic–inorganic hybrids with a high iodide/bromide content ratio, will undergo photoinduced halide phase segregation (PIHS) upon prolonged illumination. − Further, since the interconnecting layer that separates WBG and NBG cells is required to be ultrathin, the highly mobile halide ions are susceptible to halide ion exchange across layers and form undesired phases. − This process is generally referred to as an anion exchange reaction (AER) and originates because of a low thermodynamic barrier of mixing of bromide and iodide. , These processes are spontaneous and intrinsic to halide perovskites and are mediated by surface defects in perovskite nanocrystal (PNC) films and by bulk defects in annealed perovskite films. , Among all defect types, positively charged anion vacancies and negatively charged cation vacancies show relatively low formation energy, and passivating them can be a key solution to suppressing AER and PIHS. − …”

Binding of CsPbBr3 Nanocrystals to MOF-5 for the Detection of Cadmium Ions in Aqueous Media

“…The excellent optoelectronic properties exhibited by CsPbX 3 (X = Cl, Br, I) nanocrystals (CNCs) enable them to be used in interesting applications such as photovoltaic cells, light-emitting diodes, lasers, photodetectors, sensors, etc. − Fluorescence-based sensors involving CNCs have also gained popularity in recent years because they provide high specificity, good detection limits along with a fast response time, and technical simplicity. − However, the inherent ionic and dynamic nature of CNCs induces instability in them . They react to humid and oxygen environments, resulting in quick degradation and thus showing limitations toward any water-related applications or bioapplications. − Among a wide variety of CNC protection strategies, encapsulation within metal–organic frameworks (MOFs) has shown promising results …”

Manifestation of the Enhanced Photovoltaic Performance in Eco-Friendly AgBiS2 Solar Cells Using Titanium Oxynitride as the Electron Transport Layer

“…Modification of the ETL has a major role in enhancing the device performance because it can address the mis-band alignment between the photoabsorber and ETL. One can see several reports on ETL modifications to enhance charge extraction from the photoabsorber to ETL to improve the device performance. ,, Creating an ETL with suitable band structures can lead to energy level optimization and favorable alignment for optimal charge extraction, reduced interfacial and surface recombination of charge carriers, and uninterrupted charge transport in the device. However, the energy level alignment is highly dependent upon the energy level positions of the adjacent interface layers, where it enables a proper built-in potential and favors a high charge transportation in solar cells …”