Selective Passivation of Grain Boundaries via Incorporation of a Fluidic Small Molecule in Perovskite Solar Absorbers

Abstract

Additive engineering of perovskite solar absorbers has been considered an efficient protocol for fabricating highly efficient and stable solar cells. Organic additives such as polymers and small molecules efficiently passivate defect sites and thereby reduce charge trapping and recombination, which significantly improves the performance and environmental stability of perovskite devices. However, stiff polymer chains or hard organic crystals with a high transition temperature can generate pin holes via rapid phase separation from perovskite. Using liquid-phase additives during the crystallization of perovskite can assist in obtaining desirable film morphologies and passivating defect sites. Ethyl carbamate (EC) was employed in this study as a soft small-molecule additive with a low melting point (similar to 50 degrees C). Highly mobile EC molecules detach from the perovskite matrix and diffuse to the grain boundaries to reduce the boundary energy. The resulting films were composed of large grains and selectively passivated grain boundaries. The power conversion efficiency (PCE) of fabricated solar cells improved from 19.51 to 22.25% upon the incorporation of the additive. Moreover, the device exhibited an excellent PCE retention of 93.5% of the initial value for 1200 h at a relative humidity of 20%.