Limitation of Optical Enhancement in Ultra-thin Solar Cells Imposed by Contact Selectivity

Abstract

Ultra-thin crystalline silicon (c-Si) solar cell suffers both from poor light absorption and minority carrier recombination at the contacts resulting in low contact selectivity. Yet most of the research focuses on improving the light absorption by introducing novel light trapping technique. Our work shows that for ultra-thin absorber, the benefit of optical enhancement is limited by low contact selectivity. Using simulation we observe that performance enhancement from light trapping starts to saturate as the absorber scales down because of the increase in probability of the photo-generated carriers to recombine at the metal contact. Therefore, improving the carrier selectivity of the contacts, which reduces the recombination at contacts, is important to improve the performance of the solar cell beyond what is possible by enhancing light absorption only. The impact of improving contact selectivity increases as the absorber thickness scales below 20 micrometer (μm). Light trapping provides better light management and improving contact selectivity provides better photo-generated carrier management. When better light management increases the number of photo-generated carriers, better carrier management is a useful optimization knob to achieve the efficiency close to the thermodynamic limit. Our work explores a design trade-off in detail which is often overlooked by the research community.

Impact of Al2O3 Passivation on the Photovoltaic Performance of Vertical WSe2 Schottky Junction Solar Cells

“…Carriers can then be generated in a region of the semiconductor that has a recombination time constant dominated by bulk effects and can be separated by the metal/semiconductor defined electric field. Similar J SC lowering trends due to interfacial recombination were observed in published simulations that studied the thickness scaling of Si solar cells . Meanwhile, the J SC roll-off for flakes thicker than 120 nm can be explained by the fact that for active regions with thicknesses greater than the depletion region, there is little to no band bending at the air/WSe 2 interface.…”

“…The relatively lower Jsc for absorber layers thinner than 120 nm can be attributed to imperfect separation of photogenerated carriers produced near the metal/semiconductor interface. Similar Jsc lowering trends due to insufficient carrier separation were observed in published simulations that studied the thickness scaling of Si solar cells 19 . Meanwhile, the Jsc rolloff for flakes thicker than 120 nm comes from a change in the absorption characteristics.…”

Energy Management of Solar-Powered Aircraft-Based High Altitude Platform for Wireless Communications

“…Assuming the Helinet and ITU proposed position cylinders of radius 4 km and 0.61 km [41], the bank angle required to maintain an aircraft within the cylinders are approximately 1 • and 4 • respectively. At these bank angles, which can be obtained using (23), it is observed in Figure 12 that difference in the required power compared with the power required for steady level flight is negligible. Thus, all calculations and analysis in this paper applies also to HAPs flying in the defined position cylinders.…”

“…Thin film solar cells are a good technology for weight limited HAP applications. Different technologies like the ultra-thin crystalline silicon (c-Si) [23] have also been used to produced ultra-thin solar cells. Unfortunately, c-Si suffer from other factors such as poor light absorption.…”

Infrared Absorption Study of Zn–S Hybrid and ZnS Ultrathin Films Deposited on Porous AAO Ceramic Support

“…The ALD technique allows the film thickness and architecture to be controlled down to the molecular level. Nowadays, ultrathin films play a major role in devices such as microelectronic components, solar cells, LED displays, and sensors [6][7][8][9]. ALD-like surface-limiting reactions are also applied for organic compounds, enabling the molecular layer deposition (MLD) of polymers and hybrid inorganic thin films [10].…”