1 A precise ly regulating phase evolution strategy for highly efficien t kesterite solar cells

2025-04-30 0 0 2.17MB 20 页 10玖币

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A precisely regulating phase evolution strategy for highly efficient kesterite solar

cells

Jiazheng Zhou†, Xiao Xu†, Huijue Wu, Jinlin Wang, Licheng Lou, Kang Yin, Yuancai Gong, Jiangjian

Shi, Yanhong Luo, Dongmei Li*, Hao Xin*, Qingbo Meng*

J. Zhou, X. Xu, H. Wu, J. Wang, L. Lou, K. Yin, J. Shi, Y. Luo, D. Li, Q. Meng

Beijing National Laboratory for Condensed Matter Physics, Renewable Energy Laboratory

Institute of Physics, Chinese Academy of Sciences (CAS), Beijing 100190, P. R. China

E-mail: dmli@iphy.ac.cn, qbmeng@iphy.ac.cn

Q. Meng

Center of Materials Science and Optoelectronics Engineering, University of Chinese Academy of

Sciences, Beijing 100049, P. R. China

Y. Gong, H. Xin

State Key Laboratory of Organic Electronics and Information Displays & Institute of Advanced

Materials, Nanjing University of Posts & Telecommunications, Nanjing 210023 China

E-mail: iamhxin@njupt.edu.cn

J. Zhou, X. Xu, J. Wang, L. Lou, K. Yin, Y. Luo, D. Li, Q. Meng

School of Physical Sciences, University of Chinese Academy of Sciences, Beijing 100049, P. R. China

Y. Luo, D. Li, Q. Meng

Songshan Lake Materials Laboratory, Dongguan, Guangdong 523808, P. R. China

Abstract

Phase evolution during the selenization is crucial for high-quality kesterite Cu2ZnSn(S, Se)4 (CZTSSe)

absorbers and efficient solar cells. Herein, we regulate kinetic process of phase evolution from Cu+-

Sn4+-MOE (MOE: 2-methoxyethanol) system by precisely controlling positive chamber pressure. We

found that, at the heating-up stage, Se vapor concentration is intentionally suppressed in low-

temperature region, which effectively reduces collision probability between the CZTS and Se atoms,

thus remarkably inhibiting formation of secondary phases on the surface and multiple-step phase

evolution processes. This strategy enables the phase evolution to start at relatively higher temperature

and thereby leading to high crystalline quality CZTSSe absorber with fewer defects, and corresponding

CZTSSe solar cell can present 14.1% efficiency (total area), which is the highest result so far. This

work provides important insights into selenization mechanism of CZTSSe absorbers and explores a

new way of kinetic regulation strategy to simplify the phase evolution path to efficient CZTSSe solar

cells.

Keywords: CZTSSe; selenization kinetics; direct phase evolution; multi-step phase evolution

As one of the emerging solar cells, kesterite Cu2ZnSn(SxSe1-x)4 (CZTSSe) solar cell has presented 13%

of the power convention efficiency (PCE) based on environmentally friendly solution systems, which

have shown attractive application prospects1. However, large open-circuit voltage deficit (VOC, def) still

restricts the further improvement of the device performance, primarily due to complex phase

composition and high deep-level defects in the CZTSSe absorber2, 3, 4. In fact, high-temperature

selenization process is an indispensable step to complete the phase evolution of CZTSSe absorber,

which is mainly affected by Se concentration5, 6, 7, 8, reaction temperature and time9, 10, even precursor

film composition and chemical environments11, 12, and so on. Besides, multi-element component

CZTSSe has a narrow stable phase region, which usually undergoes complicated phase evolution

pathways. Different phase evolution pathways imply dissimilar intermediate phases and different

defect properties of the CZTSSe absorber13, 14, 15, 16. Therefore, precisely controlling CZTSSe phase

evolution pathways to avoid detrimental intermediate phases is the key to high crystalline quality

CZTSSe absorbers with low defects and pure kesterite phase.

Currently, some groups have already explored phase evolution process and crystal growth of the

CZTSSe absorber during the selenization reaction, from different precursor compositions14, 15, 16, local

chemical environment12, element doping17, 18, 19, 20, 21, atmosphere regulation22, 23, 24, to pressure

controlling25, 26, 27, 28, etc. These works contribute to understanding CZTSSe phase evolution and the

reason for the VOC, def to some degree. They demonstrate that, at the early heating-up stage of the

selenization reaction, gaseous Se easily reacted with the CZTS precursor film to give intermediate

phases, i.e. binary phases (CuxSe, ZnSe, SnSex) and ternary phase (Cu2SnSe3, abbreviated as CTSe)

with the temperature gradually increasing, depending on the composition of the precursor films derived

from different preparation methods, e.g. vacuum method, nanocrystalline method or solution method13,

23, 25, 29. Besides, phase evolution pathways can directly affect the formation of intermediate phases

(Fig. 1a). For example, for Cu+-Sn2+ involved precursors, its phase evolution process experienced

successively from Cu2S-ZnS-SnS to Cu2Se-ZnSe-SnSe2, then to CTSe-ZnSe, and finally to CZTSe

(Path I)15. Saucedo et al introduced Ge(IV) to stabilize Cu-Sn alloy, which phase evolution process

changed from metal stack to CTSe-ZnSe, then to CZTSe (Path II), and simultaneously avoided binary

CuxSe and SnSex intermediate phases14. Xin et al used Cu+-Sn4+ as metal precursors in DMSO

(dimethyl sulfoxide) system, which is supposed to directly change from CZTS to final CZTSe,

excluding all intermediate phases (Path III)15. These works mentioned above all focus on phase

evolution and significantly reduce VOC, def, especially Xin’s work, which achieves 13% efficient

kesterite solar cell, instilling confidence in kesterite field1. Different from the CZTSe, intermediate

phases mainly originated from Se participation in reactions at relatively lower temperatures, and

reaction rates are so fast that could be completed within 2 min30, 31. Obviously, the time window for

regulating intermediate phases is too narrow. On the other hand, most of high-efficiency CZTSSe

devices were still based on a half-closed graphite box to complete selenization reaction, which could

increase the difficulty of coordinating those parameters including temperature and Se vapor

concentration15, 20, 26. Therefore, more effective regulation strategies are urgently required to avoid

intermediate phases.

In this work, we regulate kinetic process of phase evolution by precisely tailoring a positive chamber

pressure to reduce Se vapor concentration. The collision probability between the CZTS and gaseous

Se molecule can be decreased in the low-temperature region while heating-up of the selenization

reaction. Secondary phases resulting from decomposition on the surface and multi-step phase evolution

paths are thus inhibited significantly. Additionally, this strategy enables the phase evolution to start at

relatively higher temperature and thereby leading to high crystalline quality CZTSSe absorber with

fewer defects. The bulk defects are reduced by around one order of magnitude. Finally, we achieved

CZTSSe solar cell with 14.1% PCE (total area) and a certified 13.8% PCE (total area), which is the

highest efficiency reported to date.

Understanding the CZTSSe phase evolution process

Selenization reaction of CZTS precursor films is the most important step among the fabrication

processes of the CZTSSe solar cell, which covers phase evolution and crystal growth processes.

Particularly, the phase evolution process is crucial to the CZTSSe crystal quality and defect formations.

In this work, we prepared CZTS precursor films based on Cu+-Sn4+-MOE precursor solution (MOE:

2-methoxyethanol) in air (CZTSair), which is supposed to be more suitable for mass production. When

this CZTSair film was selenized under ambient atmospheric pressure, the occurrence of hetero-

nucleation and intermediate phases was traced by interrupting at different time points. The heating-up

curve was set as follows: elevating temperature from room temperature to 350°C in 60 s, then holding

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1ApreciselyregulatingphaseevolutionstrategyforhighlyefficientkesteritesolarcellsJiazhengZhou†,XiaoXu†,HuijueWu,JinlinWang,LichengLou,KangYin,YuancaiGong,JiangjianShi,YanhongLuo,DongmeiLi*,HaoXin*,QingboMeng*J.Zhou,X.Xu,H.Wu,J.Wang,L.Lou,K.Yin,J.Shi,Y.Luo,D.Li,Q.MengBeijingNationalLaboratoryforConden...

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1 A precise ly regulating phase evolution strategy for highly efficien t kesterite solar cells

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