Bias voltage dependence of two-step photocurrent in GaAs/AlGaAs quantum well solar cells

Abstract

We investigated photoresponses of AlGaAs solar cells in which coupled GaAs quantum wells were embedded in the i-region of p-i-n diodes; we studied how the bias voltage Vb affects the normal photocurrent I generated by the visible light and a “two-step” photocurrent ΔI generated by the absorption of visible and infrared photons. We found that as Vb exceeds −0.2 V, ΔI rises and peaks at 0.6 V, while the normal photocurrent I falls to about half of its saturated level. These findings are discussed in terms of a rate equation model to show that ΔI is mainly determined by the balance of escape and recombination of photogenerated carriers.

Lifetime enhancement for multiphoton absorption in intermediate band solar cells

“…In details, the resulting intermediate band solar cell under analysis, was based on a layered structure within material and parameters found in the literature [4]. The 1 µm wider intrinsic layer and the doped contacts has been chosen to be Ga x Al 1−x As, with x = 0.3.…”

“…The photo-generation process is, mainly, a result of two interband transitions, one at the bulk region and other at the quantum wells region. However, in the latter one, to extract carriers from the confined subbands a second transition needs to take place [3,4]. Both the tunneling and the intersubband transition to continuum states, extended throughout the contacts region, can be used as such a secondary process [5,6].…”

“…The demand for renewable energy sources has been promoting the research on semiconductor solar cells [1][2][3][4][5][6][7][8][9][10][11][12]. Basically, a solar cell is formed by a p-i-n junction shed with light in order to excite charge carriers between valence and conduction bands.…”

“…A set of electronic states, called intermediate band, is introduced within the semiconductor band gap. This affords new pathways to the carriers [2][3][4], allowing additional carrier generation due to the extension of the spectral response in the energy range bellow the host-semiconductor band gap [7,8]. Consequently, the addition of the intermediate band increases the light-to-current conversion efficiency of the solar cell.…”

“…Hence, structures with ratchet states has been proposed [3][4][5]. The ratchet are states optically-and electrically-coupled to conduction band and decoupled from the valence band, acting as scattering channels for electrons excited into the intermediate band.…”