Monolithic thin-film chalcogenide–silicon tandem solar cells enabled by a diffusion barrier

Abstract

Following the recent success of monolithically integrated Perovskite/Si tandem solar cells, great interest has been raised in searching for alternative wide bandgap top-cell materials with prospects of a fully earthabundant, stable and efficient tandem solar cell. Thin film chalcogenides (TFCs) such as the Cu 2 ZnSnS 4 (CZTS) could be suitable top-cell materials. However, TFCs have the disadvantage that generally at least one high temperature step (> 500 • C) is needed during the synthesis, which could contaminate the Si bottom cell. Here, we systematically investigate the monolithic integration of CZTS on a Si bottom solar cell. A thermally resilient double-sided Tunnel Oxide Passivated Contact (TOPCon) structure is used as bottom cell. A thin (< 25 nm) TiN layer between the top and bottom cells, doubles as diffusion barrier and recombination layer. We show that TiN successfully mitigates in-diffusion of CZTS elements into the c-Si bulk during the high temperature sulfurization process, and find no evidence of electrically active deep Si bulk defects in samples protected by just 10 nm TiN. Post-process minority carrier lifetime in Si exceeded 1.5 ms, i.e., a promising implied open-circuit voltage (i-V oc) of 715 mV after the high temperature sulfurization. Based on these results, we demonstrate a first proof-of-concept two-terminal CZTS/Si tandem device with an efficiency of 1.1% and a V oc of 900 mV. A general implication of this study is that the growth of complex semiconductors on Si using high temperature steps is technically feasible, and can potentially lead to efficient monolithically integrated two-terminal tandem solar cells.

Nitride-Based Interfacial Layers for Monolithic Tandem Integration of New Solar Energy Materials on Si: The Case of CZTS

“…3 In order to achieve functional CZTS/Si monolithic devices, it has been suggested that strategies for protecting the bottom Si cell need to be developed. [3][4][5] In this work, we approach this problem through a comparative study of CZTS/Si tandem cells fabricated using three different types of TiN-based diffusion barrier layers. For the first and second, we use atomic layer deposition (ALD) to produce 5 and 10 nm TiN barrier layers, and a 10 nm TiOxNy barrier layer.…”

Spatially Resolved Optoelectronic Properties of Al-Doped Zinc Oxide Thin Films Deposited by Radio-Frequency Magnetron Plasma Sputtering Without Substrate Heating

“…This motivation sustains intensive research on alternative materials, with aluminum-doped zinc oxide (AZO) being one of the most promising choice due to the high abundance of Zn and Al [2]. For example, cost effective solar cells based on Cu (In,Ga)Se 2 (CIGS) and Cu 2 ZnSnS 4 (CZTS) absorbers have been fabricated with a TCO based on AZO [6,7]. There are several methods used to deposit AZO, including physical vapor deposition (under various operation conditions for magnetron sputtering, such as radio-frequency [8][9][10][11][12][13][14][15][16][17][18][19][20], medium-frequency [8,[21][22][23][24][25][26], DC [8,16,22,[26][27][28][29][30][31][32][33][34][35][36][37], pulsed DC [38], high power impulse [39,40], ion beam assisted [41], chemical vapor deposition [1,5] and other chemical methods such as spin coating and sol gel [2,…”

Ta Doping Effect on Structural and Optical Properties of InTe Thin Films

“…where hv refers to the incident photon energy, N A is the Avogadro's number, and d 0 is the molar concentration of the absorbing molecules (in units of M). The TPA cross-section, σ 2 , has a unit of cm 4 /(photon/s) or cm 4 s. It can also be represented by another informal unit, GM, which is defined by the following: 1GM = 10 −50 cm 4 s The calculated data are also listed in Table 4. Clearly, the value of σ 2 decreases with increasing Ta doping concentration, which is consistent with the experimental observation.…”

“…Chalcogenide thin films have drawn considerable interest in recent years, owing to their novel properties and broad range of applications in high-performance optical and electric fields, such as phase change random-access memory (PRAM), resistance random-access memory (ReRAM), nonlinear optical absorption (NOA) devices, thin-film solar cells, and so on [1][2][3][4]. Among them, group IIIA metal chalcogenide (GIIIAMC) is an important member.…”