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.

Lead-free, formamidinium germanium-antimony halide (FA4GeSbCl12) double perovskite solar cells: the effects of band offsets

“…Tuning the VBO in the simulation relates to the modication of a specic property of one layer, which could be achieved in real life through the doping of the HTL material for example (such as Spiro-OMeTAD or Cu 2 O), or by surface modication using SAM layers or other types of interfacial modiers. [41][42][43][44][45][46] When the VBO is negative, from −0.1 to −0.4 eV (i.e., VBM HTL > VBM Absorber ), a cliff-like barrier is formed at the absorber/HTL interface (see Fig. 3d).…”

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.…”