High and Low Work Function Materials for Passivated Contacts

Abstract

The tunnel oxide passivated contact (TOPCon) is a promising technology improving the efficiency of Si solar cells by cutting recombination losses and simplifying the solar cell design (1D junction design). The objective of this paper is to investigate possible contact materials having a high/low work function for passivated contacts thereby enabling the realization of a double-sided contact Si solar cell featuring n-type TOPCon on the front and p-type TOPCon at the rear side. The main part of this paper deals with the eligibility of thin atomic layer deposited (ALD) AZO (aluminum doped zinc oxide) interlayers sandwiched between n-TOPCon and ITO (tin doped indium oxide) in order to avoid sputter damage. It will be demonstrated that the insertion of ALD AZO improved the efficiency by 0.8% abs. and lead to a maximum efficiency of 20.2%. Finally, WOx and MoOx which have a high work function are identified as promising contact layers for p-TOPCon

Molybdenum and tungsten oxide: High work function wide band gap contact materials for hole selective contacts of silicon solar cells

“…This protective function is even more important for the SIS structure where the a-Si:H(p) is not present. The ability of these MoO x and WO x films to preserve surface passivation was shown for our TOPCon contacts as well [36]. Unlike for the cells with MoO x , the additional WO x contact layer significantly improves hole extraction.…”

Passivating Contacts for Crystalline Silicon Solar Cells: From Concepts and Materials to Prospects

“…Based on these properties, MoO x can be considered as part of a family of materials together with WO x [97], [98], [101], [102], and vanadium oxide (VO x ) [97], [98], [103]. These metal oxides have been used on the front side of a classical SHJ solar cell to replace the p-type a-Si:H layer [94], [97], [99], [101], [102], [104] or to improve the contact between the p-type a-Si:H layer and the TCO [102], [103], [105]. This way, a combination is cre-ated of the carrier-selective contact concepts shown in Fig.…”

“…For instance, it is well known that sputter deposition, typically used to prepare TCOs, can reduce the passivation quality of a-Si:H due to plasma damage. To prevent such damage, soft deposition methods such as ALD have been explored for the deposition of TCOs on a-Si:H [151], [165], while the same approach can be followed for a TCO deposition on poly-Si [105].…”

Integrating transparent conductive oxides to improve the infrared response of silicon solar cells with passivating rear contacts

“…Reasonable J 0,met and contact resistivity (ρ c ) values can be achieved for heavily-doped, thick poly-Si films, but here the IR response is reduced noticeably due to free carrier absorption (FCA). In this paper, we focus on low-damage sputter deposition of ITO on thin PECVD poly-Si contacts [7][8][9][10][11] with the purpose to realize an optical spacer preventing surface plasmon absorption within the subsequent metal [12]. Successively sputtering of a TCO/metal stack is an economically attractive option for the rear metallization of a monofacial cell with (i) passivation quality, (ii) electrical contact properties and (iii) infrared response being important design parameters.…”