CZTS-based materials and interfaces and their effects on the performance of thin film solar cells

Abstract

Cu2ZnSnS4 (CZTS) and its related materials such as Cu2ZnSnSe4 (CZTSe) and Cu2ZnSn(S,Se)4 (CZTSSe) have attracted considerable attention as an absorber material for thin film solar cells due to the non‐toxicity, elemental abundance, and large production capacity of their constituents. Despite the similarities between CZTS‐based materials and Cu(In,Ga)Se2(CIGS), the record efficiency of CZTS‐based solar cells remains significantly lower than that of CIGS solar cells. Considering that the difference between the two lies in the choice of the absorber material, the cause of the lower efficiency of CZTS‐based solar cells can be isolated to the issues associated with CZTS‐based materials and their related interfaces. Herein, these issues and the work done to understand and resolve them is reviewed. Unlike existing review papers, every unique region of CZTS‐based solar cells that contributes to its lower efficiency, namely: (1) the bulk of the absorber, (2) the grain boundaries of the absorber, (3) the absorber/buffer layer interface, and (4) the absorber/back contact interface are surveyed. This review also intends to identify the major unresolved issues and the potential improvement approaches of realizing sizable improvements in the solar cells' efficiency, thus providing a guide as to where research efforts should be focused. (© 2014 WILEY‐VCH Verlag GmbH &Co. KGaA, Weinheim)

The importance of back contact modification in Cu2ZnSnSe4 solar cells: The role of a thin MoO2 layer

“…10x10 cm 2 Mo coated soda-lime glasses were used as standard substrates. The substrates were cleaned with soap and submitted to sequential ultrasonic bath cleanings: acetone, isopropanol and deionized water.…”

“…In the case of CZTS, an increase in O content in the Mo back contact, via annealing in N 2 atmosphere at 550ºC for 10 min, coupled with an increase in Na content, led to a reduction of the MoS 2 layer after the thermal annealing, reducing considerably the R S [30]. A similar effect, reducing MoSe 2 thickness, has been reported to be beneficial for CZTSSe solar cells, where 1% of O 2 was incorporated to the Mo during the sputtering process [31].Thus, it can be inferred that the study of Mo oxidation processes and/or its oxides, MoO 2 and MoO 3 are highly relevant for the thin film solar cell community.…”

“…Despite this remarkable achievement, the foreseen value of 18-20% to allow for industrial production is still an ambitioned goal for the kesterite community [2][3][4]. When compared to the already commercialized and relatively close in terms of optical and electrical properties chalcogenide semiconductor CuIn 1-x Ga x Se 2 (CIGS), relevant differences have been pointed out [5][6][7].…”

“…As a result, we obtain a large improvement in solar cell performance, mainly related to a dramatic increase in V OC and FF, but also shunt resistance, R SH , linked with a remarkable change in CZTSe grain size. Furthermore, relevant structural changes in both MoSe 2 and CZTSe layers due to the presence of the MoO 2 layer will also be discussed.…”

Uniformity assessment of a 6-inch copper-zinc-tin-sulfide solar cell sputtered from a quaternary compound target

“…Although their performance is limited compared to the high-efficiency counterpart copper-indium-gallium-diselenide (CIGS) [1], the low-cost and the abundance of the raw material in addition to interesting efficiency values make it a suitable candidate for near-future industrial development [2].…”