Tailoring interdigitated back contacts for high-performance bifacial silicon solar cells

Abstract

Photovoltaic (PV) cells have become one of the most promising renewable energy technologies. To make PV more competitive with incumbent technologies, higher power output densities are needed. One promising approach is to add bifaciality to existing monofacial PV devices, allowing more output power from the additional reflection of sunlight from the ground (albedo ). For example, bifaciality can be added to Silicon Heterojunction (SHJ) solar cell with Interdigitated Back Contacts (IBC) by opening up the gaps between the back metal contacts, but the optimum gap ( ) that maximizes power output is unknown. In this paper we show that that the optimum gap ( = 1 − (1 + )( ( + )) − 1 2 ) maximizes IBC-SHJ bifacial power output ( ∝ (1 + ) (1 − 2√ ⁄ ), where is the ratio of output power density to power loss due to shadowing and Joule heating, The results are validated by self-consistent finite-element device modeling. For a typical α = 0.3, an optimized bifacial IBC SHJ cell will produce 17% more power output than state-of-the-art monofacial IBC SHJ cells. The results encourage development of bifacial IBC solar cells as a next generation PV technology.The energy output of a solar cell depends on both the solar irradiance absorbed via the photovoltaic effect, as well as its efficiency in converting photo-generated carriers into electricity. Traditional monofacial cells accept light only from the front surface; therefore, reflection from index mismatch and/or a front-contact metallic grid reduces light coupling into cells. Texturing the front surface and/or including an anti-reflection coating addresses the challenge of index mismatch, while interdigitated back-contact cells (IBC) move both n-and p-type contacts to the back to minimize front-grid light reflection. This improved light coupling allows IBC cells to achieve particularly high power output under typical illumination. By inserting high bandgap (Eg) material between absorber and highly recombination active metal contacts, Silicon heterojunction solar cells (SHJ) 1 can provide higher efficiency (η > 25%) and lower temperature coefficients 2 than traditional p-n junction solar cells. Today, despite the fact that recent market forecasts predict the rapid increase in monofacial Passivated Emitter and Rear Contact (PERC) cell production 3,4 , monofacial IBC SHJ cells ranks among the very best high-performance cells, with efficiencies exceeding 26% in experiments 5 .A new solar cell architecture, called bifacial PV, has recently emerged as a promising technological pathway to higher output yields and lower costs 4,6-9 . The bifacial design accepts light from both surfaces, therefore it allows absorption of ground reflected sunlight (albedo) at the rear side of solar cell. The sum of the direct sunlight and the albedo illumination increases photocurrent within the cell. Unfortunately, the benefits of bifacial operation of an IBC SHJ cell are not easily quantifiedafter all, the dense interdigitated grid in the back may only allow a fraction of the albedo (α) light to reach...

A review of next generation bifacial solar farms: predictive modeling of energy yield, economics, and reliability

“…In particular, unlike the opaque back sheet of monofacial solar cells, the bifacial solar cells use glass or transparent plastic back sheets. While monofacial metal contacts cover the back of the silicon solar cells, the grid on the back of bifacial solar cells is optimized for light transmission and contact resistance [38].…”

Comparative analysis of a novel low concentration dual photovoltaic/phase change material system with a non-concentrator photovoltaic system

“…It is reported that a PCM is effective in temperature reduction of CPVPCM system; it reduces cost per unit power output of the system and increases CPVPCM system's electrical and thermal efficiency [6][7][8][9][10][11][12]. Bifacial PV cells have also been employed in CPV systems due to their ability to increase power production as compared to the best efficiency mono-facial cell [16]. An extensive review on bifacial cell technology is presented in [17].…”