Prospects and performance limitations for Cu–Zn–Sn–S–Se photovoltaic technology

Abstract

While cadmium telluride and copper-indiumgallium-sulfide-selenide (CIGSSe) solar cells have either already surpassed (for CdTe) or reached (for CIGSSe) the 1 GW yr −1 production level, highlighting the promise of these rapidly growing thin-film technologies, reliance on the heavy metal cadmium and scarce elements indium and tellurium has prompted concern about scalability towards the terawatt level. Despite recent advances in structurally related copper-zinc-tin-sulfide-selenide (CZTSSe) absorbers, in which indium from CIGSSe is replaced with more plentiful and lower cost zinc and tin, there is still a sizeable performance gap between the kesterite CZTSSe and the more mature CdTe and CIGSSe technologies. This review will discuss recent progress in the CZTSSe field, especially focusing on a direct comparison with analogous higher performing CIGSSe to probe the performance bottlenecks in Earth-abundant kesterite devices. Key limitations in the current generation of CZTSSe devices include a shortfall in open circuit voltage relative to the absorber band gap and secondarily a high series resistance, which contributes to a lower device fill factor. Understanding and addressing these performance issues should yield closer performance parity between CZTSSe and CdTe/CIGSSe absorbers and hopefully facilitate a successful launch of commercialization for the kesterite-based technology.

A low-temperature order-disorder transition in Cu2ZnSnS4 thin films

“…20 The sample composition was Zn rich (Cu/Sn ¼ 1.9, Zn/Sn ¼ 1.2), comparable to that used for efficient solar cells. 1 The films are highly uniform and Raman spectra recorded at different positions are reproducible. The spectrum of the as-prepared film using a 785 nm excitation is shown in Figure 3.…”

“…1 Promising power conversion efficiencies of 12.6% were recently demonstrated for Cu 2 ZnSn(S,Se) 4 , 2 but there is room for improvement. One troubling phenomenon is the low open circuit voltage compared to the band gap.…”

Can solar power deliver?

“…Established second-generation PV technologies such as CdTe and CIGS suffer from limited availability of key elements such as indium and tellurium [25], while Si technology faces a potential shortage of silver. This situation has stimulated research into alternative thin-film material technologies based only on abundant elements, such as kesterites [21], and alternative contact materials such as copper [17]. The drive towards new semiconductors for PVs has extended to varieties of inorganic semiconductors that may be processed directly from solution [26,27].…”

“…The most interesting options are those that embody a radical change in processing or device function. Among these are devices based on molecular absorbers, such as organic heterojunctions [19] and dye-sensitized solar cells [20], both of which can be manufactured from solution; devices based on new inorganic semiconductors, especially those based on semiconductor nanoparticles that again are amenable to solution processing [21]; and devices involving semiconductor deposition through low-temperature processes on to flexible substrates [22].…”

Formation of copper tin sulfide films by pulsed laser deposition at 248 and 355 nm

“…However, due to the limited availability of elements like In and Te and the toxicity of Cd, alternative absorbers such as Cu 2 ZnSnS 4 (CZTS) are being investigated [1], and recently a thin film solar cell based on a CZTS absorber layer has reached an efficiency of 8.8% [2].…”