Potential of very thin and high‐efficiency silicon heterojunction solar cells

Abstract

Thin crystalline silicon (c‐Si) solar cells are highly attractive for realizing light‐weight and flexible wafer‐based solar cells as well as for reducing the material cost. Silicon heterojunction (SHJ) architecture using hydrogenated amorphous silicon (a‐Si:H) is suitable for realizing very thin c‐Si cells, because of its capability of excellent surface passivation. In this work, the potential of very thin c‐Si solar cells is examined by characterizing SHJ solar cells with a wide range of thicknesses from 50 to 400 μm. A trade‐off between the open‐circuit voltage (VOC) and the short circuit current density (JSC) against wafer thickness is clearly observed in these SHJ cells, whereas a decrease in fill factor (FF) is found for thin SHJ cells below 80 μm. The loss analysis for the thin SHJ cells with numerical simulation clarifies that the infrared parasitic absorption loss due to the supporting layers is enhanced for thinner wafers, which limits the JSC in the thin SHJ cells. In addition, it is confirmed that the FF is more sensitive to surface recombination than the VOC, and this tendency becomes more pronounced with the decrease in the wafer thickness. A high efficiency of 22% is achieved in a SHJ solar cell with a thickness of only 46 μm, demonstrating a high potential for flexible high‐efficiency c‐Si solar cells.

Field‐Induced Radial Junction for Dopant‐Free Crystalline Silicon Microwire Solar Cells with an Efficiency of Over 20%

“…To realize radial junctions on an MW surface, the MW radius should be larger than the depletion width induced by Al 2 O 3 . [ 3c ] The depletion width of the 10 nm thick Al 2 O 3 /n‐c‐Si junction was calculated as 900 nm using PC1D simulation, as shown in Figure S6 (Supporting Information). Accordingly, in consideration of this requirement and to maximize light absorption, in this study, the MW radius was 1 µm.…”

“…Accordingly, in consideration of this requirement and to maximize light absorption, in this study, the MW radius was 1 µm. [ 3c,22 ] The spacing and length of MW arrays were 2 and 25 µm, respectively ( Figure 3 a). In addition, to minimize the occurrence of surface reflections at the top of the MWs, their shape was modified from the conventional cylinder to a more tapered structure.…”

“…With this shortened requisite diffusion length, radial junctions alleviate the need for a high‐purity Si wafer which consumes high energy during the purification process. [ 3 ] In addition, vertically aligned MW arrays, such as those prepared for radial junctions, exhibit an antireflection effect that significantly improves c‐Si's absorption of incident light in a broad wavelength range (300–1100 nm), [ 4 ] as reported in recent studies, wherein such structures absorbed most photons in the solar spectrum. [ 5 ]…”

Improved design of InGaP/GaAs//Si tandem solar cells

“…Over the last decades, photovoltaic energy has become one important contributor to the current energy production, around 1.7% of the world power supply [1]. Thin film solar cells based on CdTe, copper indium gallium selenide (CIGS) or amorphous silicon have been developed as a cheaper alternative to crystalline silicon cells [2][3][4][5][6][7]. On the other hand, tandem cells, or multi-junction cells, as they are also called, were originally used for spacecrafts, where materials such as gallium-arsenide (GaAs) and germanium (Ge) substrates were combined for the first time to achieve high efficiencies [8][9][10].…”

Toward High Solar Cell Efficiency with Low Material Usage: 15% Efficiency with 14 μm Polycrystalline Silicon on Glass

“…This scenario necessitates alternative silicon growth and/or wafering processes. Reducing the thickness of silicon creates additional advantages, such as flexibility, reduction in weight, and higher efficiencies due to higher open‐circuit voltages ( V OC ) . Defective but low‐cost silicon can also be used as shorter minor carrier diffusion lengths are sufficient for efficient charge collection.…”