We have conducted numerical simulation of pGaN/In_{0.12}Ga_{0.88}N/nGaN, pin double heterojunction solar cell. The doping density, individual layer thickness, and contact pattern of the device are investigated under solar irradiance of AM1.5 for optimized performance of solar cell. The optimized solar cell characteristic parameters for cell area of 1 × 1 mm^{2} are open circuit voltage of 2.26 V, short circuit current density of 3.31 mA/cm^{2}, fill factor of 84.6%, and efficiency of 6.43% with interdigitated grid pattern.
The direct and tunable band gap of InGaN semiconductor offers a unique opportunity to develop high efficiency solar cell. The direct band gap of the InGaN semiconductor can vary from 0.7 to 3.4 eV [
In this paper, a simulation work is carried out to optimize pGaN/InGaN/nGaN/sapphire device structure of solar cells with 12% indium composition under AM1.5 illumination. Simulation is carried out by optimizing doping concentration and thickness of pGaN, InGaN, and nGaN layer, respectively, by changing only one material parameter at a time and keeping other parameters constant. Simulation verifies that device efficiency is strongly dependent on the intrinsiclayer (InGaN) thickness, as most of the spectrum is absorbed in this layer. We simulate pGaN/InGaN/nGaN/Sapphire solar cell to investigate the effect of incorporating grid contact pattern on the device characteristic parameter. It is observed that optimization of grid contact spacing helps greatly in device efficiency enhancement.
TCAD SILVACO, Version: ATLAS 5.16.3.R, is used for simulation. The simulator works on mathematical models which consist of fundamental equations such as Poisson’s equation, continuity equation, and transport equations. In our simulation, we have used the models such as AUGER for Auger recombination, SRH for Shockley Read Hall recombination, OPTR for optical recombination, KP model for effective masses, and band edge energies for drift diffusion simulation. Mathematical models are used in simulation which consists of fundamental equations such as Poisson’s equation, continuity equation, and transport equations. Newton’s method is used as the solution method in simulation. All the above models are used from standard TCAD library.
This paper is organized as follows: in Section
The absorption coefficient
Material parameter used in simulation.
Parameter  GaN  In_{0.12}Ga_{0.88}N  InN 

Band gap 
3.42  2.93  0.7 
Lattice constant (A°) [ 
3.18  3.23  3.6 
Minority carrier life time (ns) [ 
1  1  1 
Spontaneous polarization (sheet charge per cm^{2}) [ 



Piezoelectric polarization (sheet charge per cm^{2}) [ 
0 


Auger coefficient ntype [ 



Auger coefficient ptype [ 



The schematic diagram of InGaN/GaN pin solar cell is shown in Figure
pin InGaN/GaN double heterojunction solar cell structure.
The effect of pGaN layer thickness and doping concentration on solar cells characteristic parameters such as short circuit current density, open circuit voltage, fill factor, and efficiency is shown in Figure
Effect of pGaN layer thickness and doping concentrations on GaN/InGaN solar cell characteristic parameters: (a) short circuit current density, (b) open circuit voltage, (c) fill factor, and (d) efficiency.
The effect of doping density is analyzed by simulating the structure for different doping concentrations of 1 × 10^{16} cm^{−3}, 1 × 10^{17} cm^{−3}, and 1 × 10^{18} cm^{−3}, respectively. The simulation result shows that the short circuit current density is higher for doping concentration of 1 × 10^{16} cm^{−3}. However, it is found that
The effect of intrinsic InGaN layer thickness on solar cell characteristic parameters of pGaN/InGaN/nGaN pin solar cell is shown in Figure
Effect of InGaN layer thickness on characteristic parameters of solar cells. (a) Short circuit current density. (b) Open circuit voltage. (c) Fill factor. (d) Efficiency.
It is found that
The fill factor also starts decreasing with respect to increased InGaN layer thickness. The series resistance increases with increasing InGaN layer thickness. The efficiency curve resembles that of current density which represents the combined effect of all parameters
The final pin structure consists of ntype GaN layer, 1.5
Quantum efficiency of optimized pin GaN/InGaN double heterojunction solar cell.
We simulated the pin structure with interdigitated grid pattern, in order to further enhance the efficiency by use of grid type contact which helps in increasing the carrier collection. Simulation results of incorporating grid patterns on × and efficiency with different numbers of grid fingers such as 3, 4, and 5 and different grid spacing from 175 to 375
Characteristic parameters of simulated InGaN pin solar cell.
Contact type  Effective device area (mm^{2})  Grid spacing ( 
Indium (%) 


FF (%) 


Square pad  0.96  —  12  5.64  2.27  82  4.16 
Grid pattern  
5 grid fingers  0.90  180  12  3.26  2.17  83.6  5.92 
4 grid fingers  0.92  210  12  3.31  2.26  84.6  6.34 
3 grid fingers  0.94  260  12  3.39  2.17  83.2  6.12 
Effect of (a) short circuit current density, (b) efficiency on grid spacing for different number of grids, and (c) pin InGaN/GaN double heterojunction solar cell with grid type contact.
The optimization of pGaN/InGaN/nGaN double heterojunction pin solar cell with square contact and grid pattern is studied. The photovoltaic parameter of solar cell strongly depends on pGaN and InGaN layers thickness and doping density. Photovoltaic parameters, such as
The authors declare that there is no conflict of interests regarding the publication of this paper.
The authors gratefully acknowledge the Director of CSIRCEERI, Pilani, for his encouragement in this work. They also thank all ODG members for their help and cooperation.