Talking about the understanding of organic transport layer material spiro
The reason why organic-inorganic hybrid perovskite materials take the edge of the word "organic" is that the components contain methylammonium and formamidine ions. Using the word "organic" to describe lead-halide perovskite materials is inaccurate, because the A-site component of perovskite does not involve any organic-related properties other than the requirements for ionic radius. But if the word organic/inorganic hybrid is used to describe the device of perovskite solar cell, it is very suitable. Because the efficiency of perovskite solar cells is so high and the development is so fast, it is really inseparable from the blessing of organic semiconductor materials. Whether it is spiro-OMeTAD in upright nip devices or PTAA in inverted pin devices (of course there are many other excellent organic semiconductor materials), they are very important and even indispensable organic transport materials. Taking spiro as an example, it was the birth of the first all-solid-state perovskite solar cell based on spiro in 2012 that ignited the engine for the rapid development of perovskite. Even with efficiencies approaching 26%.

First of all, the spiro is amorphous. Of course, this is based on the consideration of film formation. The designer deliberately designed a molecular structure that is not easy to crystallize. However, the lack of crystallization leads to poor contact between molecules and obstacles to the transfer of electrons, so its own conductivity and mobility are very low, and additional doping is required to improve the electrical properties of the material. There are really a lot of literature on the selection and various attempts of spiro dopants. Generally speaking, there are the following four strategies: one is a relatively early strategy is to add oxidant to the precursor solution, A part of the spiro is oxidized and charged to improve its conductivity and mobility; the second is to add lewis acid or protonic acid to the spiro to polarize the spiro; the third is to directly pre-synthesize the salt of the spiro for use; the fourth is the most The most commonly used and most effective method is by doping LiTFSI (lithium bis-trifluoromethanesulfonimide) and TBP (tert-butylpyridine), followed by indirect slow oxidation by oxygen.

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