Efficient Charge Separation Enabled by N-Doped Graphene Quantum Dots and PCDTBT for a High-Performance Silicon Nanowire Solar Cell

Abstract

Light absorption by n-silicon nanowires (SiNWs) grown by a chemical etching method is augmented by tethering photoresponsive and highly luminescent nitrogen-doped graphene quantum dots (N-GQDs) and poly­[N-9′-heptadecanyl-2,7-carbazole-alt-5,5-(4′,7′-di-2-thienyl-2′,1′,3′-benzothiadiazole)] (PCDTBT) to a SiNW array. The resultant N-GQDs@PCDTBT@SiNW photoanode affords a wide, continuous, and intense absorption band spanning from ∼350 to 1200 nm wavelength range, enabling maximum light uptake, with a work function of ∼4.74 eV, deep enough to not serve as a charge-trapping state. Under illumination, efficient charge separation in this ternary composite is ensured by the p-type semiconducting nature of N-GQDs with a shallow valence band (VB) that allows for rapid hole extraction from the VBs of SiNW and PCDTBT and their rapid relay to the bromide ions in the electrolyte. This is simultaneously accompanied by fast, excited electron injection from N-GQDs and PCDTBT to the SiNW via a cascade process, thus minimizing back electron transfer to the tribromide ions. When the N-GQDs@PCDTBT@SiNW photoanode is coupled with a highly electrocatalytic and electrically conductive multiwalled carbon nanotube (MWCNT)@C-fabric counter electrode and a bromine/bromide electrolyte, a power conversion efficiency of 13.18% is achieved for this liquid junction solar cell, which is significantly enhanced compared to that of the SiNW/HBr,Br2/C-fabric cell (4.37%). The roles of N-GQDs, PCDTBT, and MWCNTs are independently quantified to explain the observed solar cell performance.

CoS Nanoflakes on Textured Silicon Coupled with Antimony-Decorated Tungsten Oxide for Efficient Liquid Junction Solar Cells

“…A detailed comparison of LJSCs/PECs and solid-state devices based on Si nanostructures is presented in Table S7 (Supporting Information). While PCEs in the range of 0.3–16% are reported for different configurations, − the associated stability information is provided only in very few reports. ,,− ,,,,, Among solid-state devices, while a PCE as high as ∼13% is reported for an Ag/SiNW/V 2 O 5 /Al solar cell, stabilities are not reported very well . Only two reports carry some data.…”

“…While PCEs in the range of 0.3− 16% are reported for different configurations, 59−63 the associated stability information is provided only in very few reports. 4,6,[9][10][11]14,25,29,35,36 Among solid-state devices, while a PCE as high as ∼13% is reported for an Ag/SiNW/V 2 O 5 /Al solar cell, stabilities are not reported very well. 2 Only two reports carry some data.…”

“…Liquid junction solar cells (LJSCs) based on modified n-Si are an economically viable option for efficient photo-conversion devices. Black Si electrodes, even when characterized by a high defect proportion, can still easily deliver high power conversion efficiencies (PCEs, in excess of 10%) when used as the photoanode in LJSCs, − thus highlighting their defect tolerant nature. Planar Si-based p/n junction cells do not offer this advantage.…”

Effect of Cuprous Oxide Nanocubes and Antimony Nanorods on the Performance of Silicon Nanowire-Based Quasi-Solid-State Solar Cell

“…Another notable report involved the covalent bonding of diallyl disulfide to the SiNWs via UV irradiance, imparting good air stability and PCE (7.2%) to the cell . Some of our earlier configurations comprised of decorating SiNWs with hole-transporting nanostructures such as Se NPs (7%), C@Te nanorods (11.5%), and graphene quantum dots or GQDs (13.2%). ,, However, these cells employed the HBr, Br 2 electrolyte, thus limiting their practical applications, with some improvement in stability achieved subsequently, by the use of I 3 – /I – electrolytes at the cost of cell efficiency. , In view of the above developments and lacunae, this report expounds the fabrication of a stable and an efficient solar cell, with photoactive and hole-conducting antimony nanorod (SbNR)-decorated [3-(trimethoxysilyl)­propyl]­aniline (TMSPA)-passivated SiNWs as the photoanode, an I 3 – ,I – gel enriched with Cu 2 O nanocrystals as the HTL, and with a NiO CE. The highlights of this novel solar cell are (1) the low cost, ease of availability, and low toxicity of the elements (Sb, Ni, and Cu) in the photo/electroactive materials involved, (2) the ingenious approach of dispersing Cu 2 O in the gel to improve hole transfer and transport via favorable energy level offsets, (3) the application of the highly electrocatalytic and stable NiO CE film for maximum charge separation and therefore efficiency, and (4) the high stability induced by the TMSPA self-assembled monolayer that passivates the surface suppressing the rigorous oxidation of SiNWs in the electrolyte .…”

“… 22 Some of our earlier configurations comprised of decorating SiNWs with hole-transporting nanostructures such as Se NPs (7%), C@Te nanorods (11.5%), and graphene quantum dots or GQDs (13.2%). 4 , 5 , 23 However, these cells employed the HBr, Br 2 electrolyte, thus limiting their practical applications, with some improvement in stability achieved subsequently, by the use of I 3 – /I – electrolytes at the cost of cell efficiency. 24 , 25 In view of the above developments and lacunae, this report expounds the fabrication of a stable and an efficient solar cell, with photoactive and hole-conducting antimony nanorod (SbNR)-decorated [3-(trimethoxysilyl)propyl]aniline (TMSPA)-passivated SiNWs as the photoanode, an I 3 – ,I – gel enriched with Cu 2 O nanocrystals as the HTL, and with a NiO CE.…”