Inverted Perovskite Solar Cells: Influence of Anti-Solvent Nature and Dripping Time on Perovskite Layer Properties and Uniformity

Thibault Lemercier^1,2, Lara Perrin^1,*, Emilie Planès¹, Solenn Berson² & Lionel Flandin¹
(1) Univ. Grenoble Alpes, Univ. Savoie Mont Blanc, CNRS, Grenoble INP, LEPMI, 38000 Grenoble, France
(2) Univ. Grenoble Alpes, CEA, LITEN, INES, 73375 Le Bourget-du-lac, France
* Corresponding author: lara.perrin@univ-smb.fr

Thanks to their unique properties, perovskite solar cells are particularly good candidates for tandem applications when used as the high bandgap subcells, notably in the inverted structure (called PIN), which allows lower parasitic absorption in the front contact [1]. This is thus the configuration chosen here for developing perovskite solar cells.

In this work, an investigation on the conditions of the one-step deposition method for the perovskite layer will be presented depending on the P-type material beneath it: PEDOT:PSS^a or PTAA^b. It points out the importance of the anti-solvent’s nature as well as its dripping time on the perovskite layer’s uniformity and crystalline structure. A strong impact was particularly observed in the case of perovskite layers deposited on PTAA, likely due to lower perovskite solution’s wettability on PTAA compared to PEDOT:PSS [2]. Therefore, the nature of anti-solvent has to be carefully chosen to avoid incompatibilities regarding organic sublayers and an accurate anti-solvent dripping time is a paramount parameter to finely control the final perovskite layer.

Moreover, in PIN device structures, the N-type contact almost systematically includes a fullerene layer [3], which is quite absorbent leading to unwanted parasitic absorption. We have thus also focused our attention on optically improving the N-side of the device stack. To do so, a commonly used PC₆₀BM^c / BCP^d bilayer was replaced by a PC₆₀BM / SnO₂^e bilayer all deposited by spin-coating. After optimizing both latter materials thicknesses, an improved transparent feature was observed by transmittance and reflectance measurements as well as a better stability of our cells. This bilayer is also more suitable for (monolithic) tandem applications since SnO₂ can act as a buffer layer regarding transparent conductive oxides made by PVD [1] to elaborate semi-transparent perovskite solar cells (mandatory for tandem applications).

^a Poly(3,4-ethylenedioxythiophene) polystyrene sulfonate, ^b Poly(triaryl amine), ^c [6,6]-Phenyl C61 butyric acid methyl ester, ^d Bathocuproine, ^e Tin oxide