  Radiative and non-radiative charge carrier recombination in thin-film diodes
plays a key role in determining the efficiency of electronic devices made of
next generation semiconductors such as organic, perovskite and nanocrystals. In
this work, we show that lowering the bulk recombination does not necessarily
result in enhanced performance metrics of electronic devices. From the
perspective of charge carrier extraction and injection, the radiative limit of
the open-circuit voltage of solar cells, noise current of photodetectors and
lasing threshold of injection lasers cannot be improved if the contacts are not
perfectly selective. A numerical drift-diffusion model is used to investigate
the interplay between bulk recombination and surface recombination of minority
carriers at the contacts in bipolar thin diode devices based on low-mobility
semiconductors. The surface recombination becomes prominent in case of reduced
bulk recombination strengths when non-selective contacts, i. e. contacts that
are either metallic or have imperfect charge-selective interlayer, are
employed. Finally, we derive analytical approximations for the case when
diffusion-limited surface recombination of minority carriers at Ohmic contacts
dominates the dark current. These results indicate that having perfectly
selective contacts becomes crucial in systems with suppressed bulk
recombination - a challenging requirement for future state-of-the-art thin-film
solar cells, light-emitting devices and photodetectors made of next generation
semiconductors.
