Design of UV-Absorbing Donor Molecules for Nearly Imperceptible Organic Solar Cells

Transparent
photovoltaic cells are an emerging technology that
can provide point-of-use electricity generation for building-integrated
applications. While most transparent solar cells to date target absorption
of the photon-rich near-infrared portion of the solar spectrum, these
devices compromise color neutrality and transparency because of parasitic
absorption of long-wavelength visible light. One solution to eliminate
parasitic absorption is to employ materials that absorb near-ultraviolet
light with sharper absorption cutoffs. Herein, we demonstrate organic
donor materials based on N,N′-diaryl-diamines
that incorporate a series of aryl linkers to systematically tune their
absorption profiles. When paired with acceptor 4,6-bis­(3,5-di-4-pyridinylphenyl)-2-methylpyrimidine
in an inverted architecture with an indium tin oxide top electrode
and an organic optical outcoupling layer, the three best-performing
transparent solar cells exhibit average photopic-response-weighted
transmittances of 80.3–82.0% and color-rendering indices of
95.0–97.1, both of which are records for organic photovoltaics,
with power-conversion efficiencies of 0.43–0.70%.