Scientists from Germany’s Helmholtz-Zentrum Berlin (HZB) and HTW Berlin have examined how precursor inks influence the quality of perovskite thin films. The best cells were scaled up to minimodule size. The team showed that when slot-die coating the halide perovskite layers on large areas, ribbing effects may occur but can be prevented by adjusting the precursor ink's rheological properties.
Prof. Dr. Eva Unger's team at Helmholtz-Zentrum Berlin has extensive expertise in solution-based processing methods and is investigating options for upscaling. "Perovskite photovoltaics is the best solution-processable PV technology available," says Eva Unger, "but we are only just beginning to understand how the complex interaction of the solvent components affects the quality of the perovskite layers."
When halide perovskite layers are coated on large surfaces, unwanted inhomogeneities can occur, for example so-called ribbing structures. "By varying the viscosity of the ink, such effects can be minimized," says Jinzhao Li, who is doing his PhD with Unger. At BESSY II, he has investigated how different solvent combinations affect the crystallization of the perovskite films. The best p-i-n-FAPbI3 perovskite solar cells thus achieve a certified efficiency of 22.3% on a laboratory scale. Jinzhao Li also produced mini solar modules (active area of 12.6 cm2) with colleagues from the HySPRINT innovation lab and PVcomB, which achieved efficiencies of around 17 %.
Dr. Carolin Ulbrich's team tested the optimized solar cells at PVcomB’s outdoor test facility for a whole year: In the process, the efficiency remained almost stable in winter and spring, and only dropped in the warmer summer months. "These tests of larger modules under real conditions give us valuable information on degradation mechanisms to then further improve the long-term stability of halide perovskite photovoltaics," says Eva Unger.
This work highlights the importance of the real-condition evaluation of larger area device prototypes to validate the technological potential of halide perovskite photovoltaics.