  Parameter estimation procedures provide valuable guidance in the
understanding and improvement of organic solar cells and other devices. They
often rely on one-dimensional models, but in the case of bulk-heterojunction
(BHJ) designs, it is not straightforward that these models' parameters have a
consistent physical interpretation. Indeed, contrarily to two- or
three-dimensional models, the BHJ morphology is not explicitly described in
one-dimensional models and must be implicitly expressed through effective
parameters. In order to inform experimental decisions, a helpful parameter
estimation method must establish that one can correctly interpret the provided
parameters. However, only a few works have been undertaken to reach that
objective in the context of BHJ organic solar cells. In this work, a realistic
two-dimensional model of BHJ solar cells is used to investigate the behavior of
state-of-the-art parameter estimation procedures in situations that emulate
experimental conditions. We demonstrate that fitting solely current-voltage
characteristics by an effective medium one-dimensional model can yield
nonsensical results, which may lead to counter-productive decisions about
future design choices. In agreement with previously published literature, we
explicitly demonstrate that fitting several characterization results together
can drastically improve the robustness of the parameter estimation. Based on a
detailed analysis of parameter estimation results, a set of recommendations is
formulated to avoid the most problematic pitfalls and increase awareness about
the limitations that cannot be circumvented.
