The impact of precursor water content on solution-processed organometal halide perovskite films and solar cells

Abstract

Perovskite solar cells are well known to degrade under post-fabrication stress, a.o. due to humidity as a consequence of the hydrophilic property of the organic cation. On the other hand, it has been shown that the controlled addition of water molecules during the formation of the perovskite (while starting from water-free precursor materials) yields larger perovskite crystals with less defects, resulting in better device performance. One aspect still missing in this line of research is the water content of the perovskite precursors themselves: whereas most of them are prepared with anhydrous solvents as a precaution towards premature degradation, it is still unclear whether or not the precursors really need to be dry. In this paper, the impact of the perovskite precursor's water content up to 10 vol% is investigated, in the form of a detailed study regarding the opto-electronic and morphological properties of the resulting films and devices. It is found that only modest changes occur in the films that do not affect the final photovoltaic performance, thus relaxing the conditions for large-scale production of this upcoming photovoltaic technology.loss in V oc . Additionally, if trace amounts of water would at all be trapped inside the perovskite crystal, the band gap is expected to widen rather than shrink, or at least stay unaffected, as follows from molecular dynamics simulations by Mosconi et al.. 44 As the observed PL blue-shift also points to smaller grain sizes, we surmise that the thus induced inferior local charge transport causes increased non-geminate recombination, which in turn affects the V oc . 28, 42, 45 Figure 5: Photovoltaic parameters of perovskite solar cells with active layers prepared from precursors with different water content. Error bars represent the standard deviation based on 8 devices per condition. J sc values correspond with those estimated from EQE measurements within <5% (see Fig. S2).In summary, we have investigated the influence of water contamination in organometal halide perovskite precursors on the resulting perovskite films and solar cells. The small changes that do occur in terms of morphology and optical properties of the films are found not to have considerable influence on the photovoltaic performance of devices. Our findings thus demonstrate that to obtain decently performing perovskite solar cells, in principle no precautions need to be taken concerning the anhydrous quality of the used precursor solvent. This is a far-reaching outcome as the elimination of this redundant requirement relaxes the necessary conditions for the fabrication of perovskite-based opto-electronic devices, and brings perovskite technology one step closer to large-scale production and applications.In this paper, the impact of the water content (up to 10 vol%) in DMF-based precursors for organometal halide perovskites is investigated. It is found that only modest changes occur in the films that do not affect the final photovoltaic performance, thus relaxing the conditions for large-scale product...

Structure and Growth Control of Organic–Inorganic Halide Perovskites for Optoelectronics: From Polycrystalline Films to Single Crystals

“…In another report, the water content (≤10 vol%) in perovskite precursors was found to have insignificant infl uence on the photovoltaic performance of devices. [ 76 ] More recently, polymer additives have demonstrated as a simple yet novel strategy to optimize the fi lm morphology of perovskites. [ 77 ] For instance, Su et al reported that poly(ethylene glycol) (PEG) additive can not only facilitated CH 3 NH 3 PbI 3− x Cl x precursor solution to spread out smoothly, but also retarded the growth and aggregation of perovskite crystals, both of which resulted in dense and smooth fi lms.…”

The Role of Connectivity on Electronic Properties of Lead Iodide Perovskite-Derived Compounds

“…16 Their results suggest that water has no considerable influence on the photovoltaic performance of devices. Moreover, other studies have shown that moisture during film growth is of importance to enhance the formation and quality of the hybrid perovskite films, as well as their photoluminescence (PL) performance.…”

Crystalline Clear or Not: Beneficial and Harmful Effects of Water in Perovskite Solar Cells

“…However, it should be remarked that the highest PCEs are always obtained under completely dry environmental conditions, needing encapsulation techniques as an ally factor to enhance the long-term stability under real operation conditions. [38] Grätzel and coworkers proposed also the incorporation of water additives into the N,N-dimethylformamide (DMF) solvent, leading to a controllable growth of greater grain-size and highly covered perovskite absorber, attributed to the lower boiling point and the higher vapour pressure of water compared with DMF. [37] In 2015, Conings et.…”

“…slightly modified the morphology of the perovskite films, not affecting the final photovoltaic performance and relaxing as well the conditions to scale-up the fabrication technique. [38] Grätzel and coworkers proposed also the incorporation of water additives into the N,N-dimethylformamide (DMF) solvent, leading to a controllable growth of greater grain-size and highly covered perovskite absorber, attributed to the lower boiling point and the higher vapour pressure of water compared with DMF. In addition, they show an improvement in the stability cells when water was incorporated in a certain amount.…”