Aqueous-Containing Precursor Solutions for Efficient Perovskite Solar Cells

Abstract

Perovskite semiconductors have emerged as competitive candidates for photovoltaic applications due to their exceptional optoelectronic properties. However, the impact of moisture instability on perovskite films is still a key challenge for perovskite devices. While substantial effort is focused on preventing moisture interaction during the fabrication process, it is demonstrated that low moisture sensitivity, enhanced crystallization, and high performance can actually be achieved by exposure to high water content (up to 25 vol%) during fabrication with an aqueous-containing perovskite precursor. The perovskite solar cells fabricated by this aqueous method show good reproducibility of high efficiency with average power conversion efficiency (PCE) of 18.7% and champion PCE of 20.1% under solar simulation. This study shows that water-perovskite interactions do not necessarily negatively impact the perovskite film preparation process even at the highest efficiencies and that exposure to high contents of water can actually enable humidity tolerance during fabrication in air.

Keywords: air processing; aqueous‐containing precursors; humidity; perovskites; solar cells.

Figure 1

Photograph of perovskite (CH₃NH₃PbI_{3− x}Cl_x) precursor solutions with various H₂O concentrations. a) Freshly prepared precursor solutions after filtering and b) the same precursor solution after storage overnight. Note that only the 25% H₂O solution appears cloudy after storage.

Figure 2

a) Device architecture and cross‐section SEM images of the perovskite solar cells prepared by H₂O‐20% precursor. The scale bar is 300 nm. b) Current–voltage (J–V) curves of perovskite solar cells prepared by anhydrous‐ and aqueous‐containing precursor measured under 0.971‐sun illumination. The inset shows the corresponding EQE spectra of the perovskite solar cells. c) Histograms of PCE measured for 68 separate H₂O‐20% precursor devices (black) and 51 separate anhydrous‐precursor (gray) devices.

Figure 3

Top‐view SEM images of perovskite film prepared by anhydrous precursor a) and aqueous‐containing precursor b). The scale bar is 1 µm. c) Thin‐film XRD patterns of perovskite films. d) Absorbance spectra (measured in transmission mode) and PL spectra of perovskite films.

Figure 4

a) Normalized parameters of perovskite devices fabricated under various relative humidity conditions. Error bars represent one standard deviation from the mean. b) J–V curves in the dark and under 0.971‐sun illumination (with a spectral‐mismatch factor of M = 0.971) and c) the corresponding EQE spectra of the champion devices prepared by the H₂O‐20% precursor. d) J–V curves of the champion H₂O‐20% precursor device measured in reverse and forward bias.

Figure 5

Initial device stability testing of perovskite solar cells for the a) H₂O‐20% precursor devices and the b) anhydrous‐precursor devices measured under constant simulated solar illumination (100 mW cm⁻²) at 65 °C. The devices are encapsulated and illuminated with a sulfur‐plasma lamp, without UV‐filter. Four devices of each structure were tested and all showed similar behavior. Part of the degradation mechanism is tied to the degradation of the top Ag electrode (see Figure S7 in the Supporting Information).

Figure 6

Top‐view SEM images of perovskite film before and after aging. Fresh a) and aged c) anhydrous‐precursor films; fresh b) and aged d) aqueous‐containing precursor films. The scale bar is 1 µm.