Synergetic effects of electrochemical oxidation of Spiro-OMeTAD and Li ion migration for improving the performance of n-i-p type perovskite solar cells

• Published in: Journal of materials chemistry. A, Materials for energy and sustainability Materials for energy and sustainability, 2021-03, Vol.9 (12), p.7575-7585
• Main Authors: Ding, Changzeng, Huang, Rong, Ahläng, Christian, Lin, Jian, Zhang, Lianping, Zhang, Dongyu, Luo, Qun, Li, Fangsen, Österbacka, Ronald, Ma, Chang-Qi
• Format: Article
• Language: English
• Subjects: Anodizing; Diffusion; Electrochemical oxidation; Electrochemistry; Energy conversion efficiency; Ion migration; Laser beams; Lithium ions; Mass spectrometry; Mass spectroscopy; Mathematical models; Oxidation; Perovskites; Photovoltaic cells; Secondary ion mass spectrometry; Solar cells; Tin dioxide
• ISSN: 2050-7488; 2050-7496
• DOI: 10.1039/d0ta12458c

n-i-p Type perovskite solar cells generally require air oxidation of the Spiro-OMeTAD layer to achieve high power conversion efficiency (PCE). However, the detailed oxidation mechanism is still not fully understood. In this paper, oxidation of Spiro-OMeTAD was demonstrated via a non-contact electrochemical route using UV-Vis absorption, laser beam induced current (LBIC) imaging and secondary ion mass spectrometry (SIMS) profiling of the Spiro-OMeTAD films. At the cathode, oxygen is reduced to form OH − with the help of H 2 O, while the anodic reaction is the oxidation of Spiro-OMeTAD to form Spiro-OMeTAD + . Diffusion of Li + towards the surface of the Ag electrode completes the electrochemical cycle and increases the conductivity of the hole-transporting layer. SIMS analyses of the completed devices demonstrate that the oxidation of Spiro-OMeTAD also leads to migration of Li + through the perovskite layer into SnO 2 , which supposedly leads to an increase of the built-in voltage. We verify these results by incorporation of the experimentally measured Li + concentration into a numerical drift-diffusion simulation, to replicate solar cell J - V -curves. This work provides a new insight into the oxidation of Spiro-OMeTAD in perovskite solar cells, and demonstrates that Li + migration is involved in the oxidation of Spiro-OMeTAD. Oxidation of solar cells leads to Li + ion diffusion, which increases the conductivity of the Spiro-OMeTAD layer and the built-in potential within the cells. The synergetic effects improve charge injection at both interfaces and device performance.