Dual Functional Dopant-Free Contacts with Titanium Protecting Layer: Boosting Stability while Balancing Electron Transport and Recombination Losses

Zhaolang Liu; Hao Lin; Zilei Wang; Liyan Chen; Taojian Wu; Yicong Pang; Lun Cai; Jian He; Shanglong Peng; Hui Shen; Pingqi Gao

doi:10.1002/advs.202202240

Dual Functional Dopant-Free Contacts with Titanium Protecting Layer: Boosting Stability while Balancing Electron Transport and Recombination Losses

Adv Sci (Weinh). 2022 Aug;9(23):e2202240. doi: 10.1002/advs.202202240. Epub 2022 Jun 15.

Authors

Zhaolang Liu^{1

2}, Hao Lin¹, Zilei Wang¹, Liyan Chen¹, Taojian Wu¹, Yicong Pang¹, Lun Cai¹, Jian He¹, Shanglong Peng², Hui Shen³, Pingqi Gao^{1

3

4}

Affiliations

¹ School of Materials, Sun Yat-sen University, Guangzhou, 510275, P. R. China.
² National and Local Joint Engineering Laboratory for Optical Conversion Materials and Technology, School of Materials and Energy, Lanzhou University, Lanzhou, 730000, P. R. China.
³ Institute for Solar Energy Systems, Guangdong Provincial Key Laboratory of Photovoltaic Technology, State Key Laboratory of Optoelectronic Materials and Technologies, Sun Yat-sen University, Guangzhou, 510275, P. R. China.
⁴ Jiangsu Collaborative Innovation Center of Photovoltaic Science and Engineering, Changzhou University, Changzhou, 213164, P. R. China.

Abstract

Combining electron- and hole-selective materials in one crystalline silicon (Si) solar cell, thereby avoiding any dopants, is not considered for application to photovoltaic industry until only comparable efficiency and stable performance are achievable. Here, it is demonstrated how a conventionally unstable electron-selective contact (ESC) is optimized with huge boost in stability as well as improved electron transport. With the introduction of a Ti thin film between a-Si:H(i)/LiF and Al electrode, high-level passivation (S_eff = 4.6 cm s^-1 ) from a-Si:H(i) and preferential band alignment (ρ_C = 7.9 mΩ cm² ) from low work function stack of LiF/Ti/Al are both stably retained in the newly constructed n-Si/a-Si:H(i)/LiF/Ti/Al ESC. A detailed interfacial elements analysis reveals that the efficiently blocked inward diffusion of Al from electrode by the Ti protecting layer balances transport and recombination losses in general. This excellent electron-selective properties in combination with large process tolerance that enable remarkable device performance, particularly high efficiencies of 22.12% and 23.61%, respectively, are successfully approached by heterojunction solar cells with dopant-free ESC and dopant-free contacts for both polarities.

Keywords: carrier-selective contacts; dopant-free; electron transport; heterojunction solar cells; passivating contacts.

Abstract

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