Ex situ Sn diffusion: a well-suited technique for enhancing the photovoltaic properties of a SnS absorber layer

Abstract

Sn atoms were thermally diffused into tin (II) sulfide (SnS) films prepared using chemical spray pyrolysis. This was achieved by depositing a layer of Sn metal over SnS films followed by annealing of the Sn/SnS bilayer films at 100 °C in high vacuum for 30 min. There was no contamination due to the formation of additional phases of Sn compounds up to a very high percentage of Sn diffusion. Contamination due to Sn–O–S phase was removed by Sn diffusion. The samples were optimized to achieve higher photosensitivity and low resistivity. All these enhanced properties were obtained without altering the optimum band gap of the SnS film which is suitable for maximum photovoltaic conversion efficiency.

Defect levels in SnS thin films prepared using chemical spray pyrolysis

“…Employing XPS, we have shown previously that the transition of SnS to Sn 2 S 3 takes place at larger Sn concentrations 16. In light of this, the reduction of the PL intensity of the 1134 nm peak at larger Sn concentration can be explained as the phase transition from SnS to Sn 2 S 3 and we can attribute the emission at 1.095 eV to be due to the transition from the donor level at 1.315 eV $(D_{{\rm S}}^{2 + } )$ to the acceptor level at 0.22 eV ( V Sn ).…”

“…Employing XPS, we have ensured that the evaporated thin layer of Sn has been diffused uniformly throughout the depth of the film. There was neither any X‐ray reflection peak corresponding to elemental Sn in the XRD pattern, nor any change in the optical bandgap with respect to Sn diffusion 16.…”

“…The carrier concentration was also found to be enhanced by an order of magnitude. The Sn diffusion yielded low resistive (∼2 Ω cm) as well as highly photosensitive samples, maintaining the other suitable properties of the material for photovoltaic applications (such as the optical band gap) unaffected 16. For PL measurements, a He–Ne laser (Melles Griot; 632.8 nm) with a spot size of 1 cm 2 was used to excite the sample.…”

“…As a very efficient and non‐destructive technique to probe the defect levels within the material 15, we have exploited the potential of the PL technique to understand various defect levels of SnS films. For this, certain defect levels in the material were purposefully created by ex situ Sn diffusion in SnS thin films 16. This set of Sn diffused samples along with the pristine SnS film were then analyzed using PL technique to arrive at a band scheme outlying the origin of the defect levels, by which many of the material properties of SnS can be explained.…”

Influence of Deposition Time on Structural and Optical Properties of Chemically Deposited SnS Thin Films

“…For the deposition of thin films of SnS various methods like spray pyrolysis [4][5][6][7][8][9][10], electrodeposition [11][12][13][14][15][16][17], chemical vapor deposition [18][19][20], magnetron sputtering [21], successive ionic layer adsorption and reaction (SILAR) [22], vacuum evaporation [23][24][25][26][27][28][29][30][31][32][33][34], brush plating [35][36], microwave assisted chemical deposition [37] and chemical bath deposition (CBD) [38][39][40][41][42][43][44][45][46][47][48][49][50][51][52]…”