Ihteaz Hossain1 2 Florian Mathies2 3 Tobias Abzieher2 Somayeh Moghadamzadeh2 Bryce Richards1 2 Uli Lemmer1 2 Damien Hudry1 Ulrich W. Paetzold1 2 Afshin Hadipour4

1, Institute of Microstructure Technology, KIT, Karlsruhe, Baden-Württemberg, Germany
2, Light Technology Institute, KIT, Karlsruhe, Baden-Württemberg, Germany
3, InnovationLab GmbH, Heidelberg, Baden-Württemberg, Germany
4, IMEC v.z.w., Leuven, , Belgium

Perovskite solar cells (PSC) exhibit the potential to be the next-generation thin-film photovoltaic technology, having already reached power conversion efficiencies (PCEs) of >22% for lab-scale devices within a few years. State-of-the-art PSCs utilize high temperature (> 450 °C) processed TiO2 as the electron transport layer. However, upscaling techniques such as roll-to-roll processing on flexible substrates or inkjet printing on large area devices demand low temperature fabrication routes. In this work, we tackle this challenge using TiO2 nanoparticles (TiO2-np) instead, which are synthesized at only 72 °C. The TiO2-np are crystalline in nature and the process allow precise control over particle size, doping, as well as dispersing capability in different solvents. Our results show that TiO2-np can form compact films upon spin-coating, thus reducing recombination processes at the interfaces. When spin-coated CH3NH3PbI3 is used as the perovskite absorber, devices exhibiting a high initial efficiency (> 19%) and a stabilized PCE of 18.2% (measured at constant voltage) can be realized. Furthermore, the synthesized nanoparticles demonstrate high compatibility (in terms of efficiency) with other perovskite absorber layers, including co-evaporated CH3NH3PbI3 and triple cation perovskite, Cs0.1(MA0.17FA0.83)0.9Pb(I0.83Br0.17)3. We also show that TiO2-np can be used to achieve efficient PSCs both in thin (30 nm) and thick (75 nm) layer configurations. In addition, the doping of the TiO2-np with niobium (Nb) results in a significant improvement for the thicker layers. Moreover, when dispersed in appropriate solvents, we demonstrate both inkjet printing and slot die coating processes for the TiO2-np. PSCs fabricated with such processes show high initial PCE of >17%, paving the way for high throughput and digitally printed PSCs.