Elsevier

Solar Energy

Volume 201, 1 May 2020, Pages 323-329
Solar Energy

The effect of absorber thickness on the planar Sb2S3 thin film solar cell: Trade-off between light absorption and charge separation

https://doi.org/10.1016/j.solener.2020.02.074Get rights and content

Highlights

  • The effect of absorber thickness on the Sb2S3 thin film solar cell was carefully investigated.

  • The trade-off between charge separation and light absorption in Sb2S3 device was revealed.

  • The best power conversion efficiency of 4.96% is achieved with 544 nm Sb2S3 absorber.

Abstract

Antimony sulfide Sb2S3 is an emerging photovoltaic absorber, which has been widely studied on synthesis route, device structure and interface. However, its device performance is still limited by the unoptimized Sb2S3 absorber and interface recombination, in which the neglected character of thickness is unclear. Here, the effect of absorber thickness on the Sb2S3 thin film solar cell was carefully investigated in the range of 80–620 nm, aiming to reveal the trade-off between charge separation and light absorption in the device. The characterization of JV and Sb2S3 thin film found that too thin Sb2S3 would lower the VOC and JSC, which was attributed to the severe shunt and insufficient absorption. While the too thick Sb2S3 would hinder the charge separation. This tendency was also confirmed by the performance simulation of device. Finally, the best power conversion efficiency of 4.96% is achieved with a 544 nm Sb2S3 absorber. This work provides the guidance to optimize the thickness of Sb2S3 absorber for solar cells.

Introduction

Antimony sulfide (Sb2S3) has attracted increasing attention as earth-abundant, nontoxic, and stable absorber materials (Sharma et al., 2019). It possesses the rewarding properties, such as suitable bandgap (1.5–1.7 eV), high absorption coefficient (>105 cm−1), intrinsic p-type doping, and so on. Hence the Sb2S3 is suitable for many optoelectronic applications in form of thin films, nanoparticles and nano structures. For example, Bera et al. have reported the Sb2S3 thin film/spiro-OMeTAD photodiode with a fast photoresponse time of <25 ms, which exhibits the candidate for efficient self-powered low visible light photodetector (Bera et al., 2016). The solvothermal-derived Sb2S3 nanoparticles shows high visible light degradation activity (Tao et al., 2013). While One-dimensional Sb2S3 nanostructures have also been synthesized by solvothermal method, which exhibits high photocatalytic activity of the degradation of methyl orange (Zhang et al., 2015). In addition, the outstanding optoelectrical properties of Sb2S3 make it potential to be used as absorber material in single junction or tandem solar cells (Choi et al., 2014). To date, the power conversion efficiency (PCE) of Sb2S3 sensitized device has achieved 7.5% by the Seok group (Choi et al., 2014). Another more convenient configuration of the device is planar structure, which is conducive to reduce the interface recombination. Recently, Chen group have reported the Cs-doped Sb2S3 solar cell with PCE of 6.56%, which is the highest efficiency in planar heterojunction Sb2S3 solar cells (Jiang et al., 2018:). However, there is still a huge gap between the planar Sb2S3 and commercial Cu(In, Ga)Se2, CdTe solar cell. Great efforts have been made to boost the device efficiency, which mainly focus on the synthesis routes for the high quality Sb2S3 growth. Table 1 summarizes the planar Sb2S3 device fabricated by a different method, including chemical bath deposition, solution, rapid thermal evaporation, atomic layer deposition, thermal evaporation, etc. For example, the efficiency of Sb2S3 solar cell has been improved from 2.56% to 5.5% by using chemical bath deposition (Savadogo and Mandal, 1994, Muto et al., 2013, Zimmermann et al., 2015). Chen group have also developed a facile solution for the preparation of Sb2S3 solar cell. They delivered a moderate PCE of 4.3%~6.56% (Jiang et al., 2018:, Wang et al., 2017, Zhang et al., 2018). Song have obtained the high-quality Sb2S3 thin film by rapid thermal evaporation (RTE), resulting in a PCE of 5.4% (Deng et al., 2019). Another vacuum route is atomic layer deposition, which achieved a PCE of 5.77% (Kim et al., 2014). While the thermal evaporation method demonstrated poor device performance with 450 nm Sb2S3 (Escorcia-Garcı́a et al., 2014) and delivered a PCE of 5.8% with 100 nm (Yin et al., 2019). In short, most attempts performed to promote Sb2S3 solar cells have focused on the preparation process of Sb2S3 thin films, although the device performance is still far lower than that of CIGS and CdTe thin film solar cells.

Recently, Maykel Courel et al. have tried to disclose the limited factor of PCE for Sb2S3 solar cell based on the theoretical study (Courel et al., 2019). They found that the primary obstacles for the Sb2S3 solar cells are the non-ideal series, shunt resistances, Sb2S3 non-radiative recombination and interface recombination etc. To cover those potential shortcomings, the accessible solution is the improvement of Sb2S3 bulk material quality, where many works have been reported for the synthesis of high quality Sb2S3 as discussed above. Those emerging technologies are aimed to enhance grain size, compactness and roughness of Sb2S3 thin films. However, the performance metrics of the devices are various. For example, the VOC is varied from 590 to 770 mV, while the JSC falls in the wide range of 6.1 to 17.3 mA/cm2. This drastically varies the device efficiency from 1.27% to 6.56% (Savadogo and Mandal, 1994, Muto et al., 2013, Zimmermann et al., 2015, Wang et al., 2017, Zhang et al., 2018, Deng et al., 2019, Kim et al., 2014, Escorcia-Garcı́a et al., 2014, Yin et al., 2019). Therefore, the other limiting factors behind low PCE are still unclear except for the Sb2S3 quality. Among them, the thickness of Sb2S3 might play a dominant role in solar cell performance, which will affect the absorption and carrier separation. However, the influence of the thickness of Sb2S3 on device performance is rarely studied. This can be confirmed by the previous literature study, in which diverse thickness of Sb2S3 has been adopted by different recipes (as shown in Table 1). It can be found that both very thin film (80 nm) and over thick film (3800 nm) can be delivered a PCE of 4.5–5.5% (Savadogo and Mandal, 1994, Muto et al., 2013, Zimmermann et al., 2015, Wang et al., 2017, Zhang et al., 2018, Deng et al., 2019, Kim et al., 2014, Escorcia-Garcı́a et al., 2014, Yin et al., 2019). So the optimized thickness of Sb2S3 is still suspended for high efficiency solar cell.

In this work, the Sb2S3 solar cell was assembled in the structure of ITO/TiO2/CdS/Sb2S3/Carbon/Ag, in which the Sb2S3 thin film was prepared by a low-cost hydrothermal route. This method is also called as in-situ growth process, exhibiting a facile control of thickness characteristics by reaction time tuning. Then the effect of the thickness of Sb2S3 thin film on the device performance was studied carefully, which was also confirmed by the theoretical calculation using SCAPS software. The trade-off between charge separation and light absorption in Sb2S3 solar cell was discussed thoroughly when using different thicknesses of Sb2S3 thin film. This work provides the guide for improving the planar Sb2S3 solar cell.

Section snippets

Device fabrication process

The Sb2S3 thin film solar cell was assembled with the structure of ITO/TiO2/CdS/Sb2S3/Carbon/Ag. Firstly, the ITO front contact was cleaned using detergent, acetone, alcohol and deionized water assisted with ultrasonication sequentially. Secondly, the double buffer layer TiO2/CdS films were then deposited on the ITO by solution and chemical bath deposition (CBD) method sequentially according to the previous work (Wang et al., 2019). In brief, the solution which coated on clean ITO substrates

Results and discussion

It is well known that the photoelectric conversion includes two steps: (1) the solar energy absorption and the photoexcited bound electron-hole pair. (2) the separation of electron and hole (Cai et al., 2019). Both of them will affect the PCE of the device. So the role of the thickness of Sb2S3 absorber was checked in Sb2S3 planar solar cell by varying the deposition time, where the same device structure of SLG/ITO/TiO2/CdS/Sb2S3/Carbon/Ag was adopted. The J-V parameters of the Sb2S3 thin film

Conclusion

In this work, the influence of the thickness of Sb2S3 thin film was carefully studied, in which the same device configuration and preparation process was adopted. The single variable of Sb2S3 thickness can assist to reveal the compensation between light absorption and carrier separation for solar cell. The ultra-thin Sb2S3 layer may suffer from insufficient absorption and possible pinhole, which will lower Jsc and Voc of solar cell. While the over thick Sb2S3 layer is adopted, the separation of

Declaration of Competing Interest

The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper.

Acknowledgements

This work was supported by National Natural Science Foundation of China (Grant No. 61471124), Natural Science Foundation of Fujian Province, China (Grant No. 2017J01107).

References (26)

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