A universal co-solvent dilution strategy enables facile and cost-effective fabrication of perovskite photovoltaics.

Cost management and toxic waste generation are two key issues that must be addressed before the commercialization of perovskite optoelectronic devices. We report a groundbreaking strategy for eco-friendly and cost-effective fabrication of highly efficient perovskite solar cells. This strategy involves the usage of a high volatility co-solvent, which dilutes perovskite precursors to a lower concentration (<0.5 M) while retaining similar film quality and device performance as a high concentration (>1.4 M) solution. More than 70% of toxic waste and material cost can be reduced. Mechanistic insights reveal ultra-rapid evaporation of the co-solvent together with beneficial alteration of the precursor colloidal chemistry upon dilution with co-solvent, which in-situ studies and theoretical simulations confirm. The co-solvent tuned precursor colloidal properties also contribute to the enhancement of the stability of precursor solution, which extends its processing window thus minimizing the waste. This strategy is universally successful across different perovskite compositions, and scales from small devices to large-scale modules using industrial spin-coating, potentially easing the lab-to-fab translation of perovskite technologies.

Ultrathin polymeric films for interfacial passivation in wide band-gap perovskite solar cells.

Wide band-gap perovskite solar cells have the potential for a relatively high output voltage and resilience in a degradation-inducing environment. Investigating the reasons why high voltages with adequate output power have not been realized yet is an underexplored part in perovskite research although it is of paramount interest for multijunction solar cells. One reason is interfacial carrier recombination that leads to reduced carrier lifetimes and voltage loss. To further improve the Voc of methylammonium lead tri-bromide (MAPbBr3), that has a band-gap of 2.3 eV, interface passivation technique is an important strategy. Here we demonstrate two ultrathin passivation layers consisting of PCBM and PMMA, that can effectively passivate defects at the TiO2/perovskite and perovskite/spiro-OMeTAD interfaces, respectively. In addition, perovskite crystallization was investigated with the established anti-solvent method and the novel flash infrared annealing (FIRA) with and without passivation layers. These modifications significantly suppress interfacial recombination providing a pathway for improved VOC's from 1.27 to 1.41 V using anti solvent and from 1.12 to 1.36 V using FIRA. Furthermore, we obtained more stable devices through passivation after 140 h where the device retained 70% of the initial performance value.