Spiro‐OMeTAD‐Based Hole Transport Layer Engineering toward Stable Perovskite Solar Cells

Abstract

Perovskite solar cells (PSCs) have undergone unprecedented growth in the past decade as an emerging photovoltaic technology. Up till now, the power conversion efficiency of PSCs has exceeded 25% that rivals silicon solar cells and there is still room for further enhancement. However, the development in long‐term stability lags far behind, which remains a great concern for the commercial application in the future. The device instability mainly arises from the functional components, including perovskite film, charge transport layers, and electrodes along with the involved interfaces. As the most widely studied hole transport layer at the current stage, 2,2′,7,7′‐tetrakis(N,N‐di(4‐methoxyphenyl)amino)‐9,9‐spirobifluorene (Spiro‐OMeTAD) helps contribute to the achievement of record efficiency but it weakens the device stability due to the doping‐induced side effects such as hygroscopicity and ion migration. Great efforts are devoted to boosting the stability of Spiro‐OMeTAD while maintaining excellent photovoltaic performance. In this review, the fundamental properties of Spiro‐OMeTAD have been summarized and the recent advances in engineering Spiro‐OMeTAD‐based hole transport layer for the sake of highly efficient PSCs with enhanced longevity are highlighted. In the end, an outlook for the further optimization of Spiro‐OMeTAD is provided and the issues related to large‐scale production are discussed.

Key bottlenecks and distinct contradictions in fast commercialization of perovskite solar cells

“…Currently, the high-efficiency devices are those based on the regular n-i-p structure, of which nearly pure α-FAPbI 3 and doped Spiro-OMeTAD are used as the light absorber and HTM. The issue of phase instability in α-FAPbI 3 is welldocumented, in addition to which is the additional stability induced by doped Spiro-OMeTAD [19][20][21][22]. Two typical examples can be shown below.…”

The Future of Spirobifluorene‐Based Molecules as Hole‐Transporting Materials for Solar Cells

“…Furthermore, other features such as high production costs, difficult purification steps, and short-term stability hinder the production and commercialization of large-area spiro-OMeTAD-based PSCs. Although the use of a series of doping materials has been successfully developed to overcome some of these limitations, [6,39] the aggregation of dopants during the film formation affects the stability and the performance of the perovskite-based photovoltaic devices. Under this point of view, an enhancement of the research on dopant-free HTMs for PSCs is desirable.…”

A comparative meta‐analysis of gains in efficiency in Pb‐ and Sn‐based perovskite solar cells over the last decade

“…[71] Additionally, EDTA-complexed SnO 2 and In 2 O 3 /SnO 2 bilayers were tested as electron transport layers in planar perovskite solar cells, reaching PCE values of 21.47 % and 23.24 %, respectively. [71b,72] For the hole transport layer, the by far most applied class of material are optically transparent conducting polymers, with commonly used examples 2,2',7,7'-Tetrakis[N,N-di(4-methoxyphenyl)amino]-9,9'-spirobifluorene (Spiro-OMeTAD or Spiro-MeOTAD), [73] poly(3,4-ethylenedioxythiophene) (PEDOT, often in combination with poly(styrene sulfonate) to facilitate deposition from aqueous solution) and poly-triarylamine (PTAA). To further enhance the performance of these layers they can be doped with additives such as lithium salts, cobalt complexes or 4-tertbutyl pyridine.…”