  We present data exhibiting hot spots spontaneously emerging in forward biased
thin film photovoltaics based on a-Si:H technology. These spots evolve over
time shrinking in their diameter and increasing temperature up to approximately
300 $^o$C above that of the surrounding area. Our numerical approach explores a
system of many identical diodes in parallel connected through the resistive
electrode and through thermal connectors, a model which couples electric and
thermal processes. The modeling results show that hot spots emerge collapsing
from a rather large area of nonuniform temperature, then collapse to local
entities. Finally, we present a simplified analytical treatment establishing
relations between the hot spot parameters.
