Effects of polarization charge on the photovoltaic properties of InGaN solar cells

Abstract

The effects of interface polarization charge on the photovoltaic characteristics of GaN/InGaN solar cells have been analyzed in detail using 2D drift‐diffusion simulations. The polarization charge at the GaN/InGaN interface creates an electric field that forces carriers generated by light to drift in opposite direction needed for efficient collection and substantially reduces the short circuit current (Isc) and open circuit voltage (Voc). The polarization charge plays an important role in the photovoltaic properties of InGaN solar cells comparable to that of defects. For small interface charge, the potential barrier could increase the Voc.

Numerical Study of (0001) Face GaN/InGaN p-i-n Solar Cell With Compositional Grading Configuration

“…In the new proposed structure, the abrupt current drop is eliminated until the applied bias equals to the open-circuit voltage (V oc ) for both situations of R. The conversion efficiency is enhanced due to the improvement of fill factor. The reduction of V oc is presumably due to the decrease of polarization charges [7]. The improvement of fill factor can be ascribed to the following two factors.…”

“…In light-emitting diodes (LEDs), the effect of polarization might deteriorate the electron overflow, retard the hole injection, decrease the overlap of electron and hole wavefunctions in the quantum wells (QWs), and thus degrade the LED performance [6]. As for the solar cells, it was reported recently that the carrier collection efficiency could be seriously reduced due to polarization-induced electric field, whose direction is opposite to that of the built-in electric field [7], [8], in the p-i-n structures. The J-V curve shows abrupt current drop and has quite low fill factor (FF) when the density of interface charges is high.…”

Polarization-Engineered InGaN/GaN Solar Cells: Realistic Expectations for Single Heterojunctions

“…[29], [30]. Due to the lack of experimental data for the minority carrier lifetime of InGaN alloys, the realistic and widely used [6], [7], [9], [10], [21], [22] in theoretical studies in InGaN-based solar cells value of 1 ns was assumed. In the simulations, the effect of radiative and Auger recombination is also considered.…”

“…In a polar p-i-n solar cell, polarization charges along with the inherent affinity-driven barrier at the GaN/InGaN interface deteriorate the photo-generated carrier collection, an effect which is more pronounced for higher InN MF (required for high efficiency III-nitride solar cells) or/and strain degrees [7]- [9]. In comparison to these theoretical predictions, in Fig.2 typical reported measured conversion efficiencies [8], [11], [13], [14] of p-GaN/i-InGaN/n-GaN devices, with relevant heterostructure characteristics, are shown.…”

“…Another important factor influencing the photovoltaic properties of III-nitride solar cells is the existence of significant interface p-GaN layer [13]- [18]. In such configurations, the polarization charges at the heterointerfaces generate a huge electrostatic field, whose direction is against the built-in electric field of the junction and, consequently, the efficient collection of photo-generated carriers is impeded [7], [8], [19]. Thus, the most challenging issue dealing with p-on-n structures is to mitigate the polarization-induced electric field.…”