Design of hybrid solar cell with GaAs1−xBix (x = 0.01) nanowire core and conformally coated P3HT/ITO shell

Abstract

The optoelectronic characteristics of the vertically aligned conformally coated radial junction, core–shell nanowire (NW) hybrid solar cell (HSC) having a core active layer of GaAs0.99Bi0.01as acceptor and donor shell layer of poly(3-hexylthiophene-2,5-diyl) (P3HT), have been investigated. Since axial junction solar cells (SCs) have been experimentally showing better efficiency as compared to their radial counterpart, our objective is to improve the efficiency of radial pn junction nanowire solar cells. In order to achieve that, the geometrical parameters, including the core diameter, shell thickness comprising P3HT layer and ITO for a fixed pitch of 480 nm are optimized. A fixed thickness of 10 nm is considered for P3HT due to a diffusion length of 20 nm. 3D finite-difference time-domain (FDTD) method has been employed to examine the effect of geometrical parameter variation on carrier generation and a detailed study has been presented. The core diameter of our proposed structure is 160 nm (Rcore = 80 nm) and the thickness of the surrounding shell is considered to be 90 nm (Rshell = 90 nm) for further optoelectronic performance study. The absorption spectra, generation rate profile and electric field profiles for the wavelength (λ) range of 400–900 nm have been presented for depicting the improvement caused due to incorporation of conformal coating of P3HT on core GaAs0.99Bi0.01 NW. An extensive investigation on the variation of electrical performance parameters such as open circuit voltage (Voc), short circuit current (Jsc), fill factor (FF) and power conversion efficiency (PCE) with carrier lifetime and surface recombination velocity (SRV) is performed for a fixed core and shell doping. An efficiency of 19% is achieved for the device featuring minority carrier lifetime of 60 ns and sufficiently high SRV of 105cm/s at the contacts for lightly doped core (∼1 × 1016 cm−3) and heavily doped shell (∼1 × 1019 cm−3) and substrate (∼1 × 1019 cm−3).