  Hybrid organic-inorganic halide perovskites are low-cost solution-processable
solar cell materials with photovoltaic properties that rival those of
crystalline silicon. The perovskite films are typically sandwiched between thin
layers of hole and electron transport materials, which efficiently extract
photogenerated charges. This affords high-energy conversion efficiencies but
results in significant performance and fabrication challenges. Herein we
present a simple charge transport layer-free perovskite solar cell (PSC),
comprising only a perovskite layer with two interdigitated gold back-contacts.
Charge extraction is achieved via self-assembled molecular monolayers (SAMs)
and their associated dipole fields at the metal/perovskite interface.
Photovoltages of approximately 600 mV generated by SAM-modified PSCs are
equivalent to the built-in potential generated by individual dipole layers.
Efficient charge extraction results in photocurrents of up to 12.1 mA/cm2 under
simulated sunlight, despite a large electrode spacing.
