Vapor‐Transport‐Deposited Orthorhombic‐SnSe Thin Films: A Potential Cost‐Effective Absorber Material for Solar‐Cell Applications

Abstract

The power‐conversion efficiencies of orthorhombic tin selenide (α‐SnSe)‐based thin‐film solar cells (TFSCs) are very low—less than 1% in most cases—due to the poor crystallinity, small grains, and large number of defects. Herein, the highest cell efficiency of 2.51% together with a high short‐circuit current density of 28.07 mA cm−2 for α‐SnSe TFSCs grown via vapor‐transport‐deposition (VTD) is reported. The grain size and surface roughness of the SnSe thin films greatly influence the shunt properties of the device. Significantly large shunt losses are detected in the case of both small and extremely large grains. The shunt losses for SnSe thin film with small grains are associated with high grain‐boundary scattering. The presence of extremely large grains results in high surface roughness of the SnSe thin film, which causes nonuniform deposition of the CdS buffer layer and, consequently, higher shunt losses. The SnSe thin film with moderate‐sized grains and inferior surface roughness exhibits improved shunt properties owing to uniform deposition of the CdS buffer layer and subsequent layers and thereby significant improvement in the device performance. The potential of orthorhombic VTD‐SnSe thin films as an emerging cost‐effective absorber layer for TFSCs is experimentally demonstrated.

One-Step Vapor Transport Deposition for Tuning the Photovoltaic Performance of SnSxSe1–x Solar Cells: Analysis of the Improved Voc and Jsc

“…14 More recently, we used a similar approach to synthesize an orthorhombic SnSe absorber layer by means of VTD and achieved the highest cell efficiency of ∼2.5%. 15 Our results revealed that the SnS-based devices have a higher open-circuit voltage (V oc ), while the SnSe-based devices have a higher short-circuit current density (J sc ). The high V oc of SnS-based devices can be attributed to their relatively wide optical band gap and superior shunt properties.…”

“…These observed Raman peaks agree with the previous reports. 15,29,30 The peaks of SnS x Se 1−x are shifted between SnS and SnSe; however, no peak shift trend was observed. Prominently, the strong observable peak of secondary phases was not detected from the Raman analysis.…”

“…These results imply that the pure SnS-based devices possess superior shunt properties than the pure SnSe-based devices, which explains their significantly higher V oc . 15,29,34 By contrast, the mixed-phase SnS x Se 1−x -based devices exhibited intermediate G s and J 0 values, and both values increased as the Se-content of the SnS x Se 1−x films increased. This is consistent with the trend observed in the V oc of the SnS x Se 1−x -based devices, where the V oc sharply and continuously decreased as the Se-content increased.…”

“…Over the past few years, we have developed the VTD process to grow the orthorhombic SnS absorber layer and achieved a cell efficiency of ∼4.3% . More recently, we used a similar approach to synthesize an orthorhombic SnSe absorber layer by means of VTD and achieved the highest cell efficiency of ∼2.5% . Our results revealed that the SnS-based devices have a higher open-circuit voltage ( V oc ), while the SnSe-based devices have a higher short-circuit current density ( J sc ).…”

Spiers Memorial Lecture: Next generation chalcogenide-based absorbers for thin-film solar cells

“…52 SnSe devices based on VTD-deposited absorber layers have also been recently explored, yielding 2.5% PCE. 53 Notably, selenium (∼0.05 ppm) is less abundant in the earth’s crust than sulfur (∼420 ppm), 12 which points to the fact that these Se-based materials are perhaps less likely to be compatible with multiple TW-scale deployment.…”