Engineering topics

Ali, Jazib

Publications and source records attributed to Ali, Jazib.

5 records

DOE OSTI2022

A Mixed PC 61 BM‐CO i 8DFIC Based Electron Transport Material for Inverted High‐performance Perovskite Solar Cells

Abstract This study reports a blend of [6, 6]‐phenyl‐C61‐butyric acid methyl ester (PC 61 BM) and CO i 8DFIC non‐fullerene acceptor (NFA) as an electron transport layer (ETL) in perovskite solar cells (PSCs). This mixed small‐molecule ETL showed good inter‐molecule mixing, reduced intermolecular distances and decent morphology, resulting in excellent charge carrier transport properties. Morever, charge carrier extraction and transport at the perovskite/ETL interface was optimized by reducing surface traps and defects due to the passivation ability of various terminal groups from the CO i 8DFIC molecule. A high power conversion efficiency (PCE) of 19.12 % was achieved by taking advantage of benefits from both molecules, showing much better performance than the invidual PC 61 BM or CO i 8DFIC (7.13% for using the NFA only). Moreover, the storage and ambient stabilities of the mixed ETL‐based PSCs increased dramatically compared to control devices.

Chemistry↗

DOE OSTI2021

Manipulating the Crystallization Kinetics by Additive Engineering toward High-Efficient Photovoltaic Performance

Additive processing is proven to be an effective method to improve the efficiency and stability of perovskite solar cells; however, its intrinsic role in directing the crystallization pathway and thus morphology formation remains unknown. In situ grazing-incidence wide-angle x-ray scattering (GIWAXS) is applied to study the function of a 1,8-diiodooctane (DIO) additive in manipulating the crystallization behavior of perovskite thin films. It is seen that the DIO additive could induce multi-stage intermediate crystallization phases and increases the activation energy for nucleation and growth, which postpones the perovskite phase transformation time and broadens the transition zone. The elongated crystallization process affords improved perovskite thin film crystallinity and reduces defect density, which enables a longer carrier diffusion length. As a result, improved device efficiency, moisture, and thermal stability can be achieved. The following study provides a new prospective in understanding the additive function in perovskite thin film morphology control from fundamental parameters, indicating the importance of minor processing conditions in global property management toward high device performance.

36 MATERIALS SCIENCE↗

DOE OSTI2020

Unraveling the Crystallization Kinetics of 2D Perovskites with Sandwich-Type Structure for High-Performance Photovoltaics

2D perovskite solar cells with high stability and high efficiency have attracted significant attention. A systematical static and dynamic structure investigation is carried out to show the details of 2D morphology evolution. A dual additive approach is used, where the synergy between an alkali metal cation and a polar solvent leads to high-quality 2D perovskite films with sandwich-type structures and vertical phase segregation. Such novel structure can induce high-quality 2D slab growth and reduce internal and surface defects, resulting in a high device efficiency of 16.48% with enhanced continuous illumination stability and improved moisture (55-60%) and thermal (85°C) tolerances. Transient absorption spectra reveal the carrier migration from low n to high n species with different kinetics. An [PbI 6 ] 4- octagon coalescence transformation mechanism coupled with metal and organic cations wrapped is proposed. By solvent vapor annealing, a recrystallization and reorientation of the 2D perovskite slabs occurs to form an ideal structure with improved device performance and stability.

36 MATERIALS SCIENCE↗

DOE OSTI2020

Bimolecular crystal instability and morphology of bulk heterojunction blends in organic and perovskite solar cells

The performance of polymer:fullerene bulk heterojunction (BHJ) solar cells is significantly influenced by the morphology of electron donor and acceptor blends under the premise that electronic structure is complimentary regarding donor and acceptor materials. There are many cases where intimate mixing of donor and acceptor perturbs the electronic structure, which fundamentally changes the transport and photovoltaic characteristics. In this work, we present the bimolecular crystal packing of polymers and fullerenes, and investigate the correlation between device performance and structural details. We find that bimolecular crystallization can reorganize polymer chain packing, leading to poor electron transport and device performance. The size compatibility and the passivation of entropy penalty led to cocrystallization instability, which was clearly seen by in situ GIWAXS data. PC 61 BM is found to intercalate into side chains of PQT by reorganizing both PQT and PC 61 BM, forming stable, highly ordered bimolecular crystals. The poor electron transport in bimolecular crystal domain could account for the poor device performance in both perovskite and organic solar cells. Bis-PC 61 BM, on the other hand, only forms loosely packed aggregates in solution, and then rapidly phase separated into large domains with an edge-on interfacial orientation and performed poorly in solar cells.

36 MATERIALS SCIENCE↗

DOE OSTI2020

Efficient Organic Solar Cell with 16.88% Efficiency Enabled by Refined Acceptor Crystallization and Morphology with Improved Charge Transfer and Transport Properties

Abstract Single‐layered organic solar cells (OSCs) using nonfullerene acceptors have reached 16% efficiency. Such a breakthrough has inspired new sparks for the development of the next generation of OSC materials. In addition to the optimization of electronic structure, it is important to investigate the essential solid‐state structure that guides the high efficiency of bulk heterojunction blends, which provides insight in understanding how to pair an efficient donor–acceptor mixture and refine film morphology. In this study, a thorough analysis is executed to reveal morphology details, and the results demonstrate that Y6 can form a unique 2D packing with a polymer‐like conjugated backbone oriented normal to the substrate, controlled by the processing solvent and thermal annealing conditions. Such morphology provides improved carrier transport and ultrafast hole and electron transfer, leading to improved device performance, and the best optimized device shows a power conversion efficiency of 16.88% (16.4% certified). This work reveals the importance of film morphology and the mechanism by which it affects device performance. A full set of analytical methods and processing conditions are executed to achieve high efficiency solar cells from materials design to device optimization, which will be useful in future OSC technology development.

Zhu, Lei↗