Making Record-efficiency SnS Solar Cells by Thermal Evaporation and Atomic Layer Deposition

Abstract

Tin sulfide (SnS) is a candidate absorber material for Earth-abundant, non-toxic solar cells. SnS offers easy phase control and rapid growth by congruent thermal evaporation, and it absorbs visible light strongly. However, for a long time the record power conversion efficiency of SnS solar cells remained below 2%. Recently we demonstrated new certified record efficiencies of 4.36% using SnS deposited by atomic layer deposition, and 3.88% using thermal evaporation. Here the fabrication procedure for these record solar cells is described, and the statistical distribution of the fabrication process is reported. The standard deviation of efficiency measured on a single substrate is typically over 0.5%. All steps including substrate selection and cleaning, Mo sputtering for the rear contact (cathode), SnS deposition, annealing, surface passivation, Zn(O,S) buffer layer selection and deposition, transparent conductor (anode) deposition, and metallization are described. On each substrate we fabricate 11 individual devices, each with active area 0.25 cm 2 . Further, a system for high throughput measurements of current-voltage curves under simulated solar light, and external quantum efficiency measurement with variable light bias is described. With this system we are able to measure full data sets on all 11 devices in an automated manner and in minimal time. These results illustrate the value of studying large sample sets, rather than focusing narrowly on the highest performing devices. Large data sets help us to distinguish and remedy individual loss mechanisms affecting our devices. Video LinkThe video component of this article can be found at

Measurement of contact resistivity at metal-tin sulfide (SnS) interfaces

“…More details of the film growth conditions can be found elsewhere. 12 TLM patterns were fabricated in two configurations: "superstrate" cells with metal contacts grown on top of the SnS film [ Fig. 1(a)] or "substrate" cells with SnS grown on top of the metal back contact [ Fig.…”

“…1(c). After an initial current-voltage measurement of these samples, they were annealed at 400 C in an H 2 S (10 Torr, 99.5% in N 2 ) environment for 1 h. 1,12 The same measurement was repeated both in the dark and under 100 mW cm À2 AM 1.5 illumination through the SnS layer.…”

SnS Thin Film Solar Cells: Perspectives and Limitations

“…Moreover, by depositing the SnS absorber via ALD and implementing a series of five solar cell optimization steps (aimed at reducing the photo-generated charge carriers' recombination) the same authors were able to achieve a record efficiency of 4.36% for SnS-based solar cells [10]. A slightly lower efficiency of 3.88% was obtained by the same group by vacuum evaporation [9,52]. A small list of the best efficiencies reported in literature is shown in Table 1.…”

Non-monotonic effect of growth temperature on carrier collection in SnS solar cells

“…Devices are fabricated with each annealed film using a previously reported procedure. 21 The device stack includes a thin SnO2 layer on the SnS surface and a Zn(O,S):N n-type buffer layer. Each sample contains 11 devices defined by a shadow-masked ITO pattern.…”

“…Further details on the preparation of SnS powder, preparation of Si/SiO2/Mo substrates, thermal evaporation and annealing parameters, and device fabrication steps are described in prior work. 21 We first study the impact of on the structural and electronic properties of SnS thin-films, summarized in Figure 1. The morphology of the SnS films are characterized by field-emission scanning electron microscopy (Zeiss, Ultra-55), and grain areas are extracted by analyzing manual traces 20 using the image processing software ImageJ.…”