Amine-Based Interfacial Engineering in Solution-Processed Organic and Perovskite Solar Cells

Role of Charge-Carrier Dynamics Toward the Fabrication of Efficient Air-Processed Organic Solar Cells

Over the past couple of decades, immense research has been carried out to understand the photo-physics of an organic solar cell (OSC) that is important to enhance its efficiency and stability. Since OSCs undergoes complex photophysical phenomenon, studying these factors has led to designing new materials and implementing new strategies to improve efficiency in OSCs. In this regard, the invention of the non-fullerene acceptorshas greatly revolutionized the understanding of the fundamental processes occurring in OSCs. However, such vital fundamental research from device physics perspectives is carried out on glovebox (GB) processed OSCs and there is a scarcity of research on air-processed (AP) OSCs. This review will focus on charge carrier dynamics such as exciton diffusion, exciton dissociation, charge-transfer states, significance of highest occupied molecular orbital-offsets, and hole-transfer efficiencies of GB-OSCs and compare them with the available data from the AP-OSCs. Finally, key requirements for the fabrication of efficient AP-OSCs will be presented from a charge-carrier dynamics perspective. The key aspects from the charge-carrier dynamics view to fabricate efficient OSCs either from GB or air are provided.

Advances on the Application of Wide Band-Gap Insulating Materials in Perovskite Solar Cells

In recent years, the development of perovskite solar cells (PSCs) is advancing rapidly with their recorded photoelectric conversion efficiency reaching 25.8%. However, for the commercialization of PSCs, it is also necessary to solve their stability issue. In order to improve the device performance, various additives and interface modification strategies have been proposed. While, in many cases, they can guarantee a significant increase in efficiency, but not ensure improved stability. Therefore, materials that improve the device efficiency and stability simultaneously are urgently needed. Some wide band-gap insulating materials with stable physical and chemical properties are promising alternative materials. In this review, the application of wide band-gap insulating materials in PSCs, including their preparation methods, working roles, and mechanisms are described, which will promote the commercial application of PSCs.

Prospects of glove-box versus air-processed organic solar cells

In the search for alternate green energy sources to offset dependence on fossil fuels, solar energy can certainly meet two needs with one deed: fulfil growing global energy demands due to its non-depletable nature and lower greenhouse gas emissions. As such, third generation thin film photovoltaic technology based organic solar cells (OSCs) can certainly play their role in providing electricity at a competing or lower cost than 1st and 2nd generation solar technologies. As OSCs are still at an early stage of research and development, much focus has been placed on improving power conversion efficiencies (PCEs) inside a controlled environment i.e. a glove-box (GB) filled with an inert gas such as N₂. This was necessary until now, to control and study the local nanomorphology of the spin-coated blend films. For OSCs to compete with other solar energy technologies, OSCs should produce similar or even better morphologies in an open environment i.e. air, such that air-processed OSCs can result in similar PCEs in comparison to their GB-processed counterparts. In this review, we have compared GB- vs. air-processed OSCs from morphological and device physics aspects and underline the key features of efficient OSCs, processed in either GB or air.

Improving the Performance of Polymer Solar Cells with Benzo[ghi]perylenetriimide-Based Small-Molecules as Interfacial Layers

In this study, we prepared three benzo[ghi]perylenetriimide (BPTI) conjugated molecules as electron-transporting surface-modifying layers for polymer solar cells (PSCs). These three BPTI derivatives differed in the nature of their terminal functionalities, featuring butylamine (C₃NH₂), propylammonium iodide (C₃NH₃I), and butyldimethylamine (C₃DMA) units, respectively. We evaluated the optoelectronic properties of PTB7-Th: PC₇₁BM blends modified with these interfacial layers, as well as the performance of resulting PSCs. We used UV-Vis spectroscopy, atomic force microscopy, surface energy analysis, ultraviolet photoelectron spectroscopy, and photoelectric flow measurements to examine the phenomena behind the changes in the optoelectronic behavior of these blend films. The presence of a BPTI derivative changed the energy band alignment at the ZnO-active layer interface, leading to the ZnO film behaving more efficiently as an electron-extraction electrode. Modifying the ZnO surface with the BPTI-C₃NH₃I derivative resulted in a best power conversion efficiency (PCE) of 10.2 ± 0.53% for the PTB7-Th:PC₇₁BM PSC (cf. PCE of the control device of 9.1 ± 0.13%). In addition, modification of a PM6:Y6:PCBM PSC with the BPTI-C₃NH₃I derivative increased its PCE from 15.6 ± 0.25% to 16.5 ± 0.18%. Thus, BPTI derivatives appear to have potential as IFLs when developing high-performance PSCs, and might also be applicable in other optoelectronic devices.

Interfacial modification towards highly efficient and stable perovskite solar cells

Organic-inorganic perovskite solar cells (PSCs) have attracted tremendous attention due to their high absorption coefficient, high carrier mobility, long diffusion length, and tunable direct bandgap, and their excellent efficiency was boosted to a certified 25.2% efficiency in 2019. However, due to the presence of a high-density of charge traps in perovskite films, plenty of charge recombination occurs at grain boundaries and defects caused by precursor compositions, the process of preparation and crystal growth, thereby restricting the power conversion efficiency (PCE). At present, interfacial modifications by using additives play an important role in various breakthroughs of PSCs. Herein, the effects of various additives with the main types of functional groups, length and spatial configuration of molecules on interfacial modifications in PSCs are reviewed, and their influences on perovskite crystallization and film formation, defect passivation in the bulk and/or at the surface, stabilities of PSCs, and adjusting the interface of structures and energy levels for device performances are also described and summarized. Finally, an outlook of interfacial modifications is provided on the selection and design of efficient additives with respect to the fabrication and development of highly efficient and stable PSCs.

Two-Stage Ultraviolet Degradation of Perovskite Solar Cells Induced by the Oxygen Vacancy-Ti4+ States

The failure of perovskite solar cells (PSCs) under ultraviolet (UV) irradiation is a serious barrier of commercial utilization. Here, a two-stage degradation process of TiO₂-based PSCs is discovered under continuous UV irradiation in an inert atmosphere. In the first decay stage, oxygen vacancy-Ti³⁺ (Ti³⁺-V_O) transform into active Ti⁴⁺-V_O trap states under UV excitation and cause photocarrier loss. Furthermore, Ti⁴⁺-V_O states can convert back into Ti³⁺-V_O states through oxidizing I⁻, which result in the accumulation of I₃⁻. Sequentially, the rapid decomposition of perovskite accelerated by increasing I₃⁻ replaces the photocarrier loss as the dominant mechanism leading to the second decay stage. Then, a universal method is proposed to improve the UV stability by blocking the transformation of Ti³⁺-V_O states, which can be realized by polyethyleneimine ethoxylated (PEIE) modified layer. The optimized devices remain ∼75% of its initial efficiency (20.51%) under UV irradiation at 72 days, whereas the normal devices fail completely.

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A two-stage degradation process of TiO₂-based PSCs under continuous UV irradiation

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The transformation of Ti³⁺-V_O to Ti⁴⁺-V_O states is responsible for the UV degradation

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A universal method to enhance the UV stability of PSCs was proposed