Artiom Magomedov

A Methoxydiphenylamine‐Substituted Carbazole Twin Derivative: An Efficient Hole‐Transporting Material for Perovskite Solar Cells

The small-molecule-based hole-transporting material methoxydiphenylamine-substituted carbazole was synthesized and incorporated into a CH3NH3PbI3 perovskite solar cell, which displayed a power conversion efficiency of 16.91%, the second highest conversion efficiency after that of Spiro-OMeTAD. The investigated hole-transporting material was synthesized in two steps from commercially available and relatively inexpensive starting reagents. Various electro-optical measurements (UV/Vis, IV, thin-film conductivity, hole mobility, DSC, TGA, ionization potential) have been carried out to characterize the new hole-transporting material.

Amorphous Hole‐Transporting Material based on 2,2′‐Bis‐substituted 1,1′‐Biphenyl Scaffold for Application in Perovskite Solar Cells

Perovskite solar cells are considered a promising technology for solar-energy conversion, with power conversion efficiencies currently exceeding 20 %. In most of the reported devices, Spiro-OMeTAD is used for positive-charge extraction and transport layer. Although a number of alternative hole-transporting materials with different aromatic or heteroaromatic fragments have already been synthesized, a cheap and well-performing hole-transporting material is still in high demand. In this work, a two-step synthesis of a carbazole-based hole-transporting material is presented. Synthesized compounds exhibited amorphous nature, good solubility and thermal stability. The perovskite solar cells employing the newly synthesized material generated a power conversion efficiency of 16.5 % which is slightly lower than that obtained with Spiro-OMeTAD (17.5 %). The low-cost synthesis and high performance makes our hole-transport material promising for applications in perovskite-based optoelectronic devices.

Long-Term Stability of the Oxidized Hole-Transporting Materials used in Perovskite Solar Cells

The vast majority of the hole transporting materials require the use of chemical doping as an essential step for preparation of efficient perovskite solar cells. An oxidized organic hole-transporting material, obtained during a doping procedure, could potentially be one of the weak links in the device composition. It is not uncommon for the solar cell to heat up under summer sun; therefore, all device components must possess some degree of resistance to repetitive thermal stress. In the current publication, a series of oxidized hole-transporting materials have been synthesized and their long-term stability investigated. During thermal stability testing of the films, kept at 100 °C under an inert atmosphere, it was observed that oxidized HTMs start to degrade and partly revert to original unoxidized material. It is known that oxidized HTM, formed during doping, is responsible for the increased conductivity and ultimately for better efficiency of hole extraction process in the PSC device; therefore, observed instability of the oxidized HTMs in the thin films at elevated temperatures could be one of the causes of drop in conductivity reported for the doped spiro-OMeTAD. It could also potentially be one of the reasons why perovskite solar cells lose their efficiency under prolonged thermal stress.

Nonspiro, Fluorene‐Based, Amorphous Hole Transporting Materials for Efficient and Stable Perovskite Solar Cells

Abstract Novel nonspiro, fluorene‐based, small‐molecule hole transporting materials (HTMs) V1050 and V1061 are designed and synthesized using a facile three‐step synthetic route. The synthesized compounds exhibit amorphous nature with a high glass transition temperature, a good solubility, and decent thermal stability. The planar perovskite solar cells (PSCs) employing V1050 generated an excellent power conversion efficiency of 18.3%, which is comparable to 18.9% obtained with the state‐of‐the‐art Spiro‐OMeTAD. Importantly, the devices based on V1050 and V1061 show better stability compared to devices based on Spiro‐OMeTAD when aged without any encapsulation under uncontrolled humidity conditions (relative humidity around 60%) in the dark and under continuous full sun illumination.

Pyridination of hole transporting material in perovskite solar cells questions the long-term stability

In this work, for the first time, reactive radical-cation species present in hole-transporting materials were shown to react with tert-butylpyridine additive, routinely used in hole transporting layer composition. As a result, new pyridinated products were isolated and characterized by NMR and MS analysis. Additionally, their optical and photophysical properties (i.e., solid-state ionization potentials (Ip), cyclic voltammetry (CV), UV/vis characteristics, and conductivities) were determined. Formation of the pyridinated products was confirmed in the aged perovskite solar cells by means of mass spectrometry, and shown to have negative influence on the overall device performance. We believe that these findings will help improve the stability of perovskite devices by either molecular engineering of hole-transporting materials or utilization of less-reactive or sterically hindered pyridine derivatives.

Efficient and Stable Perovskite Solar Cells Using Low‐Cost Aniline‐Based Enamine Hole‐Transporting Materials

Metal-halide perovskites offer great potential to realize low-cost and flexible next-generation solar cells. Low-temperature-processed organic hole-transporting layers play an important role in advancing device efficiencies and stabilities. Inexpensive and stable hole-transporting materials (HTMs) are highly desirable toward the scaling up of perovskite solar cells (PSCs). Here, a new group of aniline-based enamine HTMs obtained via a one-step synthesis procedure is reported, without using a transition metal catalyst, from very common and inexpensive aniline precursors. This results in a material cost reduction to less than 1/5 of that for the archetypal spiro-OMeTAD. PSCs using an enamine V1091 HTM exhibit a champion power conversion efficiency of over 20%. Importantly, the unsealed devices with V1091 retain 96% of their original efficiency after storage in ambient air, with a relative humidity of 45% for over 800 h, while the devices fabricated using spiro-OMeTAD dropped down to 42% of their original efficiency after aging. Additionally, these materials can be processed via both solution and vacuum processes, which is believed to open up new possibilities for interlayers used in large-area all perovskite tandem cells, as well as many other optoelectronic device applications.