Effects of potassium doping on solution processed kesterite Cu2ZnSnS4 thin film solar cells

Tong, Zhengfu; Yan, Chang; Su, Zhenghua; Zeng, Fangqin; Yang, Jia; Li, Yi; Jiang, Liangxing; Lai, Yanqing; Liu, Fangyang

doi:10.1063/1.4903500

Cited by 109 publications

(82 citation statements)

References 29 publications

Supporting

Mentioning

Contrasting

Unclassified

Order By: Relevance

“…[ 2a , 8 ] The (112) preferred orientation and crystallinity of the CZTS fi lms are enhanced through doping K atoms, and in addition, some secondary phases such as ZnS are also surpressed. [ 8 ] Because of the high concentration of Ca within soda lime glass, its effect on the CZTS devices have also been investigated. [ 9 ] However, no obvious infl uences on CZTS device performance were observed, which was attributed to the +2 oxidation state of Ca.…”

Section: Doi: 101002/aenm201502386mentioning

confidence: 99%

Efficiency Enhancement of Cu₂ZnSn(S,Se)₄ Solar Cells via Alkali Metals Doping

Hsieh

Han

Jiang

et al. 2016

Advanced Energy Materials

119

View full text Add to dashboard Cite

should be related to their +1 oxidation state. [ 9 ] Therefore, all alkali metals with the +1 oxidation state are expected to have positive effect on CZTSSe solar cells. However, no systematic studies have been reported on the effects of alkali metals dopants so far.In this paper, a systematic research of alkali-metals doping effects on CZTSSe solar cells performances was reported. Alkali metal-containing precursors were utilized to investigate various infl uences of alkali metals on CZTSSe solar cells. K-doped CZTSSe solar cells showed the best device performance in our research. Various thicknesses of CdS fi lms were deposited on K-passivated CZTSSe surface in order to further improve the solar cell effi ciency. Finally, over 8% PCE of K-doped CZTSSe solar cell with around 35 nm CdS has been reached.The major X-ray diffraction (XRD) peaks of the undoped CZTSSe fi lm shown in Figure 1 a can be indexed to zincblende CZTSe . [ 10 ] All (112) diffraction peaks of each of the alkali-metal-doped samples shifted to small diffraction angles comparing with the undoped sample (Figure 1 b). Because the reduction of diffraction angle represents the lattice constant increase, this means that we could raise lattice constants of CZTSSe by doping alkali metal. The larger lattice constant is attributed to the alkali metal atoms occupying Cu vacancy ( V Cu ) or substituting positions of CZTSSe atoms. Interestingly, the variation of diffraction angle is not linearly related to the radius of the alkali-metals. (112) peaks left-shift from an order of Li, Na, and then K-doped sample, whereas the (112) peak positions of Rb and Cs-doped samples shift back to larger diffraction angles. This indicates that the relatively smaller alkali-metal atoms could occupy the V Cu or substitute CZTSSe atoms, but it becomes diffi cult to replace CZTSSe atoms for Rb and even more so for Cs because of their larger atoms radii. (112) peak shift of Li-doped samples is the smallest among the alkali-metal-dopants. The Li ion radius (0.59 Å) is the same as Cu and Zn ion (0.60 Å), so the small shift should be mainly attributed to Li ions occupying the V Cu . Raman spectra of the selenized fi lms with and without doping alkali metals were shown in Figure S1 (Supporting Information). Intense Raman shifts at 172, 195, and 238 cm −1 attributed to Cu 2 ZnSnSe 4 phase were observed.[ 11 ] According to this observation, Raman spectra have proved that there is no secondary phase introduced when we intentionally doped alkali elements into CZTSSe fi lms. Besides, as the primary characteristic peaks in the Raman spectra do not change, the S/Se ratio is considered as constant for undoped and each of the alkali-doped samples, which further supports the fact that the shift of XRD peaks is not induced by the dissimilar degree of the selenization. Figure 2 shows the scanning electron microscopy (SEM) images of the alkali-metal-doped and undoped samples. TheCopper based direct band gap semiconductors used as thinfi lm photovoltaic materials have been investigated for a long...

show abstract

Section: Doi: 101002/aenm201502386mentioning

confidence: 99%

Efficiency Enhancement of Cu₂ZnSn(S,Se)₄ Solar Cells via Alkali Metals Doping

Hsieh

Han

Jiang

et al. 2016

Advanced Energy Materials

119

View full text Add to dashboard Cite

show abstract

“…9,18) Moreover, some reports claimed that Na doping enhances the crystallinity of absorber thin films and the short-circuit current of thin-film solar cells. [19][20][21] Although the positive effects of Na doping in CIGS-based solar cells have been extensively studied, those in CZTSbased solar cells are still unclear.…”

mentioning

confidence: 99%

Photocarrier dynamics in undoped and Na-doped Cu₂ZnSnS₄single crystals revealed by ultrafast time-resolved terahertz spectroscopy

Phuong

Okano

Yamashita

et al. 2015

Appl. Phys. Express

View full text Add to dashboard Cite

We investigated the effects of sodium doping on the photocarrier dynamics in Cu 2 ZnSnS 4 (CZTS) single crystals using optical pump-THz probe transient reflectivity (THz-TR) and time-resolved photoluminescence (PL) spectroscopy. The THz-TR and PL decay dynamics are influenced by sodium doping, and their sodium-induced changes are consistent with each other. These time-resolved measurements revealed that the lifetime of photocarriers increases with sodium doping. This result indicates that a part of defects is suppressed by doping sodium into CZTS and implies that sodium doping improves the charge transport properties of CZTS, leading to an improvement in the performance of CZTS-based solar cells.

show abstract

“…[7] First studies on the effect of potassium addition confirmed advantageous effects on kesterite absorber growth and optoelectronic properties similar to Na. [8,9] Several studies comparing different alkali elements and their effect on solar cell properties and device performance have recently been published. [10][11][12][13] Table 1 compares the effects on device performance by extracting a ranking of the various alkali elements in each publication in the order of their capability to improve device performance.…”

mentioning

confidence: 99%

Complex Interplay between Absorber Composition and Alkali Doping in High‐Efficiency Kesterite Solar Cells

Haass

Andrés

Figi

et al. 2017

Advanced Energy Materials

107

View full text Add to dashboard Cite

kesterite material with its optimal bandgap and absorption coefficient. [2] Alkali treatment of kesterite solar cells is one of the measures to reduce the high V OC -deficit and most of today's >10% efficiency kesterite devices utilize the beneficial effects of alkali elements on absorber layer morphology and optoelectronic properties. So far the most research attention has been paid to sodium, resulting in many thorough investigations which revealed grain size enhancement, passivation of grain boundaries, and an increase in net hole concentration as the major beneficial effects of sodium treatments. [3][4][5][6] Also lithium addition has shown to improve device performance by boosting the electronic quality of the CZTSSe absorber material and grain boundaries. [7] First studies on the effect of potassium addition confirmed advantageous effects on kesterite absorber growth and optoelectronic properties similar to Na. [8,9] Several studies comparing different alkali elements and their effect on solar cell properties and device performance have recently been published. [10][11][12][13] Table 1 compares the effects on device performance by extracting a ranking of the various alkali elements in each publication in the order of their capability to improve device performance. It is apparent from these rankings that no consistent experimental results have been obtained, which triggers two questions: (i) Why do the published results differ so much? (ii) Which alkali element possesses the highest potential for efficiency improvements?This paper aims to unveil the discrepancy between the recently published results comparing the effects of alkali treatments on device performance. Our hypothesis is that each alkali element requires a different absorber composition to achieve the highest PV performance and we therefore prepared a comprehensive set of samples with different alkali elements and alkali concentrations as well as various metal ratios. All samples were thoroughly characterized by scanning electron microscopy (SEM), X-ray diffraction (XRD), X-ray fluorescence (XRF), inductively coupled plasma-mass spectrometry (ICP-MS), as well as current-voltage (J-V), capacitance-voltage (C-V), time-resolved photoluminescence (TRPL), and external quantum efficiency (EQE) measurements.The methodology used for absorber synthesis is based on the solution process described elsewhere, [14] allowing for accurate alkali incorporation by simply adding alkali chlorides to the solution. [15] Figure 1a illustrates the matrix of sample compositions prepared with five different alkali elements: lithium (Li), Sodium treatment of kesterite layers is a widely used and efficient method to boost solar cell efficiency. However, first experiments employing other alkali elements cause confusion as reported results contradict each other. In this comprehensive investigation, the effects of absorber composition, alkali element, and concentration on optoelectronic properties and device performance are investigated. Experimental results show that in the r...

show abstract

Effects of potassium doping on solution processed kesterite Cu2ZnSnS4 thin film solar cells

Cited by 109 publications

References 29 publications

Efficiency Enhancement of Cu₂ZnSn(S,Se)₄ Solar Cells via Alkali Metals Doping

Efficiency Enhancement of Cu₂ZnSn(S,Se)₄ Solar Cells via Alkali Metals Doping

Photocarrier dynamics in undoped and Na-doped Cu₂ZnSnS₄single crystals revealed by ultrafast time-resolved terahertz spectroscopy

Complex Interplay between Absorber Composition and Alkali Doping in High‐Efficiency Kesterite Solar Cells

Contact Info

Product

Resources

About

Effects of potassium doping on solution processed kesterite Cu2ZnSnS4 thin film solar cells

Cited by 109 publications

References 29 publications

Efficiency Enhancement of Cu2ZnSn(S,Se)4 Solar Cells via Alkali Metals Doping

Efficiency Enhancement of Cu2ZnSn(S,Se)4 Solar Cells via Alkali Metals Doping

Photocarrier dynamics in undoped and Na-doped Cu2ZnSnS4single crystals revealed by ultrafast time-resolved terahertz spectroscopy

Complex Interplay between Absorber Composition and Alkali Doping in High‐Efficiency Kesterite Solar Cells

Contact Info

Product

Resources

About

Efficiency Enhancement of Cu₂ZnSn(S,Se)₄ Solar Cells via Alkali Metals Doping

Efficiency Enhancement of Cu₂ZnSn(S,Se)₄ Solar Cells via Alkali Metals Doping

Photocarrier dynamics in undoped and Na-doped Cu₂ZnSnS₄single crystals revealed by ultrafast time-resolved terahertz spectroscopy