Photoanode Modification Based on Lignin Extracted from Rice Husk for Dye-Sensitized Solar Cells

The photoanode optimization of dye-sensitized solar cells (DSSCs) has been developed to create renewable devices based on green chemistry. TiO2 plays a crucial role in light absorption, charge separation, and electron transport within the photoanode of DSSCs. Modifying mesoporous TiO2 photoanode using lignin-template has been considered a viable option for photocatalyst synthesis. Lignin derived from rice husk is a potential material due to its abundant sources in many countries. Therefore, in this work, rice husk lignin was employed for non-toxic and low-cost material performance improvement of TiO2. Experimental results showed that the best efficiency and current density were identified as the effect of adding a 5% concentration of lignin on the TiO2 composite, namely 4.81% PCE.


Introduction
Increasing the performance of various electronic applications has been developed using biomass that has not been utilized, such as activated carbon from candlenut shells for electromagnetic wave absorbers [1] and coconut shell for anechoic chambers [2,3].The availability of abundant biomass is one of the aspects considered for the applications that can be produced in large quantities.Rice husk is one of the sources of renewable biomass that can be utilized.In 2020, about 518 million tons of rice were produced worldwide, 90 % of which occurred in Asia.In the processing process, the amount of rice husk produced globally can be estimated at 150 million tons [4].Rice husk has a lignin component of around 12-21% [5] which can be used as a semiconductive polymer dopant for photoanode in photovoltaic devices and improve the photoconversion efficiency of the cell [6].Photoanode is a working electrode comprising a mesoporous wideband-gap semiconductor layer.The dopant added to the metal oxides, the commonly reported effects of TiO 2 doping are the increase of charge transport and the decrease of charge recombination.In addition, it was found that a small amount of dopant can enhance the dye adsorption capability of TiO 2 nanoparticles compared to nondoped TiO 2 [7].Lignin utilization could control the size and distribution of the nanoparticles and increases the surface area of TiO 2 which needed to optimize dye adsorption on the TiO 2 [6].Furthermore, the development of lignin-based modification following the evidence of lignin-based extraction from the self-growing plant (Lily) [8] and commercial lignin [9] for TiO 2 templates has shown improved performance due to enhanced light harvesting, enhanced electron transport, and increased surface area and pore structure.In this work, we have prepared a lignin isolation process with specific and easy extraction for achieving pure lignin.The Klason method was used for the rice husk lignin extraction process [10] due to several advantages, namely standardized procedure, simplicity, specific to acid-insoluble lignin, and applicability to various types of biomass.The result of lignin powder was applied to the TiO 2 composite with several lignin powder concentrations, namely 2.5%, 5%, 7.5%, 10%, 15% and then characterized for showing the detail device performance of dye sensitized solar cell.

Isolation Lignin from Rice Husk
The process of isolating rice husk lignin (figure 1) begins with grinding to form rice husk powder and dispersing it in 1 M sodium hydroxide (NaOH) solution at a ratio of 1:12 (wt:v) with a stirring process at 80 ⁰C for 4 h.Then, the solution resulting from alkaline hydrolysis (AH) is washed with distilled water until it reaches a neutral pH.The resulting solid residue is filtered manually (decantered) and the filtrate is taken as a dark liquid (black liquor).Acidification of the filtrate with H 2 SO 4 solution (72%) was carried out until it reached pH 4 by adding 15 ml several times and waiting for precipitation to occur.Then, the precipitate is filtered and washed using distilled water until the pH is neutral.Furthermore, it was baked in an oven at 60⁰C to remove the water content.Fluorine-doped tin oxide (FTO) acetone, and ethanol for 15 min.3200 Ultrasonic Cleaner Waterbath) for 15 minutes.Subsequently, FTO glass substrates were immersed into a 40mM aqueous TiCl and post-TiCl 4 on composite deposition TiO of TiO 2 -lignin composite used stirring plate at 60 Deposition of TiO 2 -lignin was then spun at 3500 rpm for 30 s (active area, 0.25cm of TiO 2 -lignin deposited by spin coating method following variation of lignin concentrations, namely 2.5%, 5%, 7.5%, 10%, 15%. Lignin Isolation Process from Rice Husk using the Klason Method with TiO 2 -Lignin Photoanode Modification doped tin oxide (FTO) was washed sequentially with Teepol detergent, deionized water, acetone, and ethanol for 15 min.Then, the substrate was sterilized using UV Ozone 3200 Ultrasonic Cleaner Waterbath) for 15 minutes.Subsequently, FTO glass substrates were immersed into a 40mM aqueous TiCl 4 solution at 70⁰C for 30 minutes for the treatment of on composite deposition TiO 2 -lignin and rinsed with deionized water.lignin composite used stirring plate at 60⁰C for 4 hours which was prepared firstly.
was then spun at 3500 rpm for 30 s (active area, 0.25cm lignin deposited by spin coating method following variation of lignin concentrations, namely Addition of H 2 SO 4 ethod was washed sequentially with Teepol detergent, deionized water, Then, the substrate was sterilized using UV Ozone treatment (Branson 3200 Ultrasonic Cleaner Waterbath) for 15 minutes.Subsequently, FTO glass substrates were ⁰C for 30 minutes for the treatment of pre-TiCl 4 nin and rinsed with deionized water.The fabrication which was prepared firstly.was then spun at 3500 rpm for 30 s (active area, 0.25cm 2 ).The composite lignin deposited by spin coating method following variation of lignin concentrations, namely Addition of NaOH

FTIR spectra of lignin
This current study investigates the effect of lignin-based rice husk on TiO 2 composites for the photovoltaic performance of DSSCs.The FT-IR spectrum analysis characterization of the functional group from the extraction of rice husk lignin using the Klason method proved that some of the constituent elements of lignin were detected with the peaks of the functional groups of Ester S-OR, Amine C-N, Alkena C=C, Aliphatic Stretching Clusters -CH-, Phenolic functional O-H as shown in Figure 2.

Figure 2. FT-IR Spectra of Rice Husk Lignin
The results of lignin isolation were then compared with the standard and commercial lignin namely Commercial lignin (Aldrich) [11] as shown in Table 1.Based on the identification analysis of the characteristic peaks on the FTIR spectrum, it turned out that the lignin isolated from rice husk has several functional groups in common with standard commercial lignin from Aldrich.The typical peaks include the S-OR ester with 500-540 cm -1 wave numbers.The IR spectrum isolated from rice husk has a typical absorption peak of the S-OR ester at wave number 570.93 cm -1 , while the absorption peak is typical for Aldrich commercial lignin at wave number 499.831 cm -1 .The IR absorption peak for the Amine C-N functional group with wave numbers 1000-1250cm -1 , the IR spectrum isolated from rice husk has a typical absorption peak for Amine C-N at wave number 1099.43 cm -1 , but was not found in Aldrich commercial lignin.Furthermore, the IR absorption peak for the C=C Alkene functional group with wave numbers 1630 -1680 cm -1 .The IR spectrum isolated from rice husk has a typical Alkene C=C absorption peak at wave number 1637.56 cm -1 , while the absorption peak is typical for Aldrich commercial lignin in wave number 1608.34 cm -1 .The IR absorption peak for aliphatic -CH-and aromatic stretching groups is at wave number 2900 cm -1 , the IR spectrum isolated from rice husk has a typical -CH-aliphatic and aromatic stretching absorption peak at wave number 2924.09 cm -1 , while the absorption peak is typical for the same commercial lignin Aldrich 2930.17 cm -1 .The stretching IR absorption peak for the Phenolic functional O-H with wave numbers around 1500 -1600 cm -1 , is present in the IR spectrum of rice husk lignin at the Phenolic functional O-H wave number 3448.72 cm -1 , and the IR spectrum of Aldrich lignin appears in 3436.62 cm .Thus, based on the FTIR spectrum, rice husk lignin is compatible with the commercial lignin produced by Aldrich.

Solar cell performance
In order to evaluate the electrical properties of DSSC with the addition of lignin as a natural polymer, the I-V curves were used to show device performance.A control sample that constitutes a DSSC without lignin was also compared with similar fabrication.Figure 3 displays the experimentally measured current density-voltage (J-V) characteristics.Additionally, Table 2  The fill-factor (FF) has an average value that is greater on the device with the addition of lignin compared to the device with pristine TiO 2 , which increases from 53.4% to 57.3% (TiO 2 -lignin 5%) for the highest value as shown in Figure 3.This shows rice husk lignin does not increase the device's resistance.The cell of TiO 2 -Lignin 5% presented a better result than other lignin concentrations and the cell of pristine TiO 2 , with a value of V OC that of 0.669 V.A larger V OC may be related to slow recombination and better electron collection efficiency.The performance of the device with pristine TiO 2 photoanode has a power conversion efficiency (PCE) of 5.07% with the short-circuit current (J SC ) of 14.35 mA/cm

Conclusion
The results of the characterization of rice husk lignin extract using the Klason method were displayed via the FTIR spectra.The FTIR measurement showed absorption peaks similar to the commercial lignin product Aldrich.The photoanode modification using rice husk lignin achieved the best performance at 5% lignin concentration in the TiO 2 -lignin composite, namely 4.81% PCE, and not much different in device performance with pristine TiO 2 photoanode with 5.07% PCE.In summary, a composite between semiconductor and organic polymers (lignin in this case) are potential alternatives for photoanodes in the field of dye-sensitized solar cells (DSSCs).Low cost, renewability, and conjugated structure are the most important features of organic polymers for their application in photovoltaics.

Tabel 1 .
Comparison of the Wavelength Spectrum of Rice Husk Lignin with Aldrich Standard Lignin

Figure 3 .
Figure 3.The J-V Curves of DSSC with Pristine TiO 2 and Various Concentrations of TiO 2 -Lignin Measured by Sun Simulator (100 mW/cm 2 AM 1.5G)

Table 2 .
Electrical Parameters for Photoanode of DSSC with Pristine TiO 2 and Composite of TiO 2 - 2. The photoanode modification with rice husk lignin with 5% lignin concentration provides the best performance with PCE of 4.81% and J SC of 12.56 mA/cm 2 .