Open Access Version

Abstract:
Organic-inorganic hybrid perovskites with adjustable bandgap show promising potential as tandem top cells to pair with silicon bottom cells as they achieve power conversion efficiencies (PCEs) over 33%, while the fabrication costs are likely to stay low. To date, the most efficient perovskite layers are fabricated by spin coating, which is difficult to scale up to industrial wafer size, and the crystallization process remains difficult to control. In this work, Cs0.22FA0.78)Pb(I0.85Br0.15)3 + 5 mol% MAPbCl3 was reported on slot-die coating for an efficient 1.68 eV wide bandgap triple-halide (3halide) absorber. A suitable solvent system was designed and optimized specifically for the slot-die coating technique. This thesis demonstrated that with this recipe, our fabrication route enabled a bandgap of 1.68 eV, which was suitable for tandem solar cells, and without phase segregation typically observed into iodine-rich and bromide-rich phases. The slot-die coated wet perovskite film was dried using a stream of nitrogen (N2) from an ”N2 knife” with high reproducibility, which avoided the need to use antisolvents. This thesis explored varying drying and annealing conditions from 100°C to 170°C and measured absolute as well as transient photoluminescence (PL) to extract information about the perovskite bandgap, quasi-Fermi level splitting (QFLS), and charge carrier lifetimes. This thesis found parameters allowing to crystallize the perovskite film into large grains reducing charge collection losses and thus enabling higher current density in solar cells. With annealing at 150°C, an optimized tradeoff was found between crystallization and the detrimental formation of PbI2 platelets on the film’s top surface. In-situ Grazing-Incidence Wide-Angle X-ray Scattering (GIWAXS) investigation of the solution intermediate and film annealing at various stages unveiled the perovskite crystallization and PbI2 formation processes in comparison of two coating recipes (spin coating recipe and slot-die coating recipe) and two quenching methods (antisolvent and N2 quenching) with the influence of annealing temperature. With the optimized annealing conditions, this work improved perovskite single junction cells’ cell stability and performance towards a stabilized power output of up to 19.4% (0.16 cm2). By integrating the optimized perovskite fabrication with commercial saw damage etched Czochralski silicon bottom cells, a two-terminal monolithic tandem solar cell with a PCE of 25.2% on 1 cm2 active area was demonstrated with fully scalable processes fabricated on a 120 μm thin wafer. The time-resolved and wavelength-resolved surface photovoltage (SPV) was utilized to understand the high fill factor and the charge extraction dynamics for perovskite interplaying with two types of silicon bottom cell concepts. Furthermore, a fully scalable 4 cm2 tandem solar cell was developed with screen-printed silver front grids, yielding PCE up to 24%. For the solar cells, the loss mechanisms as well as guidelines are presented for further improving the printed films. Several strategies were attempted to control the PbI2 excess and improve the perovskite/C60 interface with more suitable band alignment. Overall, this thesis emphasized the significant promise of slot-die coating as a viable method for producing scalable and industrially relevant perovskite/silicon tandem solar cells.