Abstract
A two-dimensional finite-element model was developed to simulate the optoelec- tronic performance of thin-film, p-i-n junction solar cells. One or three p-i-n junctions filled the region between the front window and back reflector; semiconductor layers were made from mixtures of two different alloys of hydrogenated amorphous silicon; empirical relation- ships between the complex-valued relative optical permittivity and the bandgap were used; a transparent-conducting-oxide layer was attached to the front surface of the solar cell; and a metallic reflector, either flat or periodically corrugated, was attached to the back surface. First, frequency-domain Maxwell postulates were solved to determine the spatial absorption of photons and thus the generation of electron-hole pairs. The AM1.5G solar spec- trum was taken to represent the incident solar flux. Second, drift-diffusion equations were solved for the steady-state electron and hole densities. Numerical results indicate that increasing the number of p-i-n junctions from one to three may increase the solar-cell efficiency by up to 14%. In the case of single p-i-n junction solar cells, our simulations indicate that efficiency may be increased by up to 17% by incorporating a periodically corrugated back reflector (as opposed to a flat back reflector) and by tailoring the bandgap profile in the i layer. © The Authors. Published by SPIE under a Creative Commons Attribution 3.0 Unported License. Distribution or reproduction of this work in whole or in part requires full attribution of the original pub- lication, including its DOI. (DOI: 10.1117/1.JPE.6.025502)
Highlights
The global cumulative installed photovoltaic capacity reached 180 GW by the end of the year 2014.1 More than 90% of the photovoltaic market is based on bulk-silicon solar cells,[1] as manufacturing costs continue to fall.[2]
Our numerical studies reveal that changing from a periodically corrugated back reflector to a flat back reflector makes very little difference to the performance of the triple p-i-n junction solar cell considered here
We have investigated the effects of a. a multiplicity of p-i-n junctions; b. periodic corrugation of the back reflector; and c. periodic nonhomogeneity in the i layer(s)
Summary
The global cumulative installed photovoltaic capacity reached 180 GW by the end of the year 2014.1 More than 90% of the photovoltaic market is based on bulk-silicon solar cells,[1] as manufacturing costs continue to fall.[2]. If electrical issues trump any gain in photon absorption, a chosen light-management strategy will not be fruitful.[5] Typically, theoretical research on the optical characteristics of thin-film photovoltaic solar cells is focused on the calculation of the short-circuit current density but not the open-circuit voltage, thereby overplaying the EHP generation rate by not taking the EHP recombination rate into account. We decided to develop a combined optical–electrical model to investigate thin-film solar cells comprising one or more p-i-n junctions,[28,29] periodically corrugated metallic back reflectors,[30] and nonhomogeneous i bandgap profiles.[31] In the optical part of the model, light absorption is calculated by solving the frequency-domain Maxwell postulates, while the electrical part of the model solves for the steady-state carrier density distribution.
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