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Glass and edge seal encapsulation of a perovskite solar cell to enable stability through damp heat and thermal cycling tests.

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We report the fabrication of monolithic all-perovskite tandem solar cells with a stabilized power conversion efficiency of 19.1% and demonstrate improved thermal, atmospheric, and operational stability of the tin–lead perovskite (FA0.75Cs0.25Sn0.5Pb0.5I3) used as the low gap absorber.

The rapid rise in efficiency and tunable bandgap of metal-halide perovskites makes them highly attractive for use in tandems on silicon. Recently we demonstrated a perovskite–silicon monolithic two-terminal tandem with 23.6% power conversion efficiency. Here, we present work on optical optimization to improve light harvesting that includes thinning out the top transparent electrode to reduce front-surface reflection and parasitic absorption; introducing metal fingers to minimize series resistance losses; and further minimizing reflection loss with a polydimethylsiloxane (PDMS) stamp with random, pyramidal texture. Additionally, to reduce voltage loss while achieving current matching, we employ poly­[bis­(4-phenyl)­(2,4,6-trimethylphenyl)­amine] (PTAA) as a hole transport material instead of NiO x and a wider 1.68 eV bandgap perovskite composition. These optimizations boost the open-circuit voltage to 1.77 V and the short-circuit current density to 18.4 mA/cm2, culminating in a 25% efficient perovskite–silicon tandem with a 1 cm2 active area.

Significant effort has focused on controlling the deposition of perovskite films to enable uniform films, enabling efficiencies to climb dramatically. However, little attention has been paid to the evolution of thin-film stresses during deposition and the consequent effect on film morphology. While a textured surface topology has potential benefits for light scattering, a smooth surface is desirable to enable the pinhole-free deposition of contact layers. We show that the highly textured morphology made by popular antisolvent conversion methods arises because of in-plane compressive stress experienced during the intermediate phase of film formation where the substrate constrains the film from expandingleading to energy release in the form of wrinkling, resulting in trenches that can be hundreds of nanometers deep with periods of several micrometers. We demonstrate that the extent of wrinkling is correlated with the rate of film conversion and that ultrasmooth films are obtained by slowing the rate of film formation.

One of the most appealing features of solar cells made from hybrid organic–inorganic perovskites is that they can be processed directly from solution, leading to low cost, energy-efficient processing. Numerous studies have shown that the composition of these solutions and the choice of solvent (or solvent blend) affects the efficiency of the resulting solar cell. Despite the importance of this correlation for performance, the choice of solvent(s) used to deposit the perovskite precursors has been largely a matter of experimental trial-and-error. In this work, we present a coherent theory explaining the molecular origin of the efficacy of solvent choice, which lends itself to the creation of a fast quantum mechanical-based screening process that facilitates the design of effective new solvents. We also provide the first theoretical confirmation of complexation of HOIP precursors in solution, including their structure and relative stability. We show that the Mayer bond order of a solvent’s polar atoms predicts the solubility of the perovskite lead halide precursors in the solvent much more reliably than the relative polarity and Hansen polar solubility parameter suggested in the literature as being figures of merit.

A review on the versatility of atomic layer deposition and chemical vapor deposition for the fabrication of stable and efficient perovskite solar cells.