  Choosing the Indium Gallium Nitride (InGaN) ternary alloy for thin films
solar cells might yield high benefits concerning efficiency and reliability,
because its bandgap can be tuned through the Indium composition and radiations
have little destructive effect on it. It may also reveal challenges because
good quality p-doped InGaN layers are difficult to elaborate. In this letter, a
new design for an InGaN thin film solar cell is optimized, where the player of
a PIN structure is replaced by a Schottky contact, leading to a Metal-IN (MIN)
structure. With a simulated efficiency of 19.8%, the MIN structure performs
better than the previously studied Schottky structure, while increasing its
fabrication tolerance and thus functional reliability a. Owing to its good
tolerance to radiations [1], its high light absorption [2, 3] and its
Indium-composition-tuned bandgap [4, 5], the Indium Gallium Nitride (InGaN)
ternary alloy is a good candidate for high-efficiency-high-reliability solar
cells able to operate in harsh environments. Unfortunately, InGaN p-doping is
still a challenge, owing to InGaN residual n-doping [6], the lack of dedicated
ac-ceptors [7] and the complex fabrication process itself [8, 9]. To these
drawbacks can be added the uneasy fabrication of ohmic contacts [4] and the
difficulty to grow the high-quality-high-Indium-content thin films [10] which
would be needed to cover the whole solar spectrum. These drawbacks still
prevent InGaN solar cells to be competitive with other well established III-V
and silicon technologies [11]. In this letter, is proposed a new Metal-IN (MIN)
InGaN solar cell structure where the InGaN p-doped layer is removed and
replaced by a Schottky contact, lifting one of the above mentioned drawbacks. A
set of realistic physical models based on actual measurements is used to
simulate and optimize its behavior and performance using mathematically
rigorous multi-criteria optimization methods, aiming to show that both
efficiency and fabrication tolerances are better than the previously described
simple InGaN Schottky solar cell [12].
