<h3>Title</h3>
<h3><span style="font-size: 12.16px;">Cu<sub>2</sub>ZnSnS<sub>4</sub>: A potential photovoltaic material for low-cost thin film solar cell</span></h3>
<p><strong><span style="font-size: 12.16px;"><span style="text-decoration: underline;">Abstract</span> :</span></strong></p>
<p style="text-align: justify;"><span style="font-family: 'Times New Roman', serif; font-size: 10pt; text-align: justify; text-indent: 36pt;">Shifting to renewable energy is the solution for meeting the ever-increasing energy demand as well as preventing the deterioration of the environment due to the use of fossil fuel-based energy sources. The Sun from which abundant energy is received on the Earth is probably the most promising renewable energy source. A solar photovoltaic (PV) device converts the solar radiation directly into electricity. Such as device is comprised of a photo-absorber material that absorbs incident photons and uses their energy for raising the chemical potential of electrons within the material. Other materials interfaced with this photo-absorber help collect these excited electrons at one end of the PV device and thereby help generate a potential difference.</span></p>
<p style="text-align: justify;"><span style="text-align: justify; text-indent: 36pt; font-size: 10pt; line-height: 115%; font-family: 'Times New Roman', serif;" lang="EN-US">Silicon has been the semiconductor of choice for the role of photo-absorber in a PV device, however, due to lower absorption coefficient (α =10<sup>3</sup> cm<sup>−1</sup>; λ &lt; 825 nm) and brittleness, several other materials and related PV technologies have been developed. Among these, the technologies based on CdTe and Cu(In,Ga)Se<sub>2</sub> (CIGSe) semiconductors have been commercially successful with a photoconversion efficiency  of more than 20 %. However, the concerns associated with toxic element Cd and less abundant elements In and Ga have propelled the investigation for alternative semiconductors. A quaternary compound Cu<sub>2</sub>ZnSnS<sub>4</sub> (CZTS) is a promising candidate owing to the facts that all the elements used in it are non-toxic and have relatively abundant availability; moreover, it has a high absorption coefficient (α =10<sup>4</sup> cm<sup>−1</sup>; λ &lt; 825 nm) and close to an optimum band gap (</span><span style="text-align: justify; text-indent: 36pt; font-size: 10pt; line-height: 115%; position: relative; top: 4.5pt;" lang="EN-US"><img src="file:///C:/Users/DCS/AppData/Local/Temp/msohtmlclip1/01/clip_image002.gif" border="0" width="16" height="19" /></span><span style="text-align: justify; text-indent: 36pt; font-size: 10pt; line-height: 115%; font-family: 'Times New Roman', serif;" lang="EN-US"> = 1.5 eV).</span></p>
<p style="text-align: justify;"><span style="text-align: justify; text-indent: 36pt; font-size: 10pt; line-height: 115%; font-family: 'Times New Roman', serif;" lang="EN-US">In the present talk, the challenges associated with the synthesis of CZTS thin films via solution chemistry will be discussed and ways to eliminate/control them have been suggested. First, in order to obtain a film with a desired surface morphology, a combined use of the chloride and acetate salts of copper in the precursor solution has been found to be helpful. Further to this, a capping layer of ZnS was necessary on top of the precursor film in order to obtain a CZTS thin film with controlled surface morphology. The CZTS film prepared by this strategy had a stoichiometric composition, the grain size of the order of ~ 200 nm, </span><span style="text-align: justify; text-indent: 36pt; font-size: 10pt; line-height: 115%; position: relative; top: 4.5pt;" lang="EN-US"><img src="file:///C:/Users/DCS/AppData/Local/Temp/msohtmlclip1/01/clip_image002.gif" border="0" width="16" height="19" /></span><span style="text-align: justify; text-indent: 36pt; font-size: 10pt; line-height: 115%; font-family: 'Times New Roman', serif;" lang="EN-US"> = 1.5 eV, and a high hole-carrier density ~ 10<sup>19</sup> cm<sup>−3</sup>.</span></p>
<p style="text-align: justify;"><span style="font-family: 'Times New Roman', serif; font-size: 10pt; text-align: justify; text-indent: 36pt;">Further, the tuning of electrical and optical properties of the CZTS via incorporation of silver (Ag) at copper sub-lattice sites in CZTS will be discussed. Thin films of the resulting pentanary alloys (Ag</span><sub style="font-family: 'Times New Roman', serif; text-align: justify; text-indent: 36pt;">1-<em>x</em></sub><span style="font-family: 'Times New Roman', serif; font-size: 10pt; text-align: justify; text-indent: 36pt;">Cu</span><em style="font-family: 'Times New Roman', serif; font-size: 10pt; text-align: justify; text-indent: 36pt;"><sub>x</sub></em><span style="font-family: 'Times New Roman', serif; font-size: 10pt; text-align: justify; text-indent: 36pt;">)</span><sub style="font-family: 'Times New Roman', serif; text-align: justify; text-indent: 36pt;">2</sub><span style="font-family: 'Times New Roman', serif; font-size: 10pt; text-align: justify; text-indent: 36pt;">ZnSnS</span><sub style="font-family: 'Times New Roman', serif; text-align: justify; text-indent: 36pt;">4</sub><span style="font-family: 'Times New Roman', serif; font-size: 10pt; text-align: justify; text-indent: 36pt;"> (0 ≤ </span><em style="font-family: 'Times New Roman', serif; font-size: 10pt; text-align: justify; text-indent: 36pt;">x</em><span style="font-family: 'Times New Roman', serif; font-size: 10pt; text-align: justify; text-indent: 36pt;"> ≤ 1) show a remarkable change in their microstructure and electronic properties with increasing Ag content. Going from Cu</span><sub style="font-family: 'Times New Roman', serif; text-align: justify; text-indent: 36pt;">2</sub><span style="font-family: 'Times New Roman', serif; font-size: 10pt; text-align: justify; text-indent: 36pt;">ZnSnS</span><sub style="font-family: 'Times New Roman', serif; text-align: justify; text-indent: 36pt;">4</sub><span style="font-family: 'Times New Roman', serif; font-size: 10pt; text-align: justify; text-indent: 36pt;"> (</span><em style="font-family: 'Times New Roman', serif; font-size: 10pt; text-align: justify; text-indent: 36pt;">x</em><span style="font-family: 'Times New Roman', serif; font-size: 10pt; text-align: justify; text-indent: 36pt;"> = 0) to Ag</span><sub style="font-family: 'Times New Roman', serif; text-align: justify; text-indent: 36pt;">2</sub><span style="font-family: 'Times New Roman', serif; font-size: 10pt; text-align: justify; text-indent: 36pt;">ZnSnS</span><sub style="font-family: 'Times New Roman', serif; text-align: justify; text-indent: 36pt;">4</sub><span style="font-family: 'Times New Roman', serif; font-size: 10pt; text-align: justify; text-indent: 36pt;"> (</span><em style="font-family: 'Times New Roman', serif; font-size: 10pt; text-align: justify; text-indent: 36pt;">x</em><span style="font-family: 'Times New Roman', serif; font-size: 10pt; text-align: justify; text-indent: 36pt;"> = 1), the grain size increased from 0.2 to 2 μm which has been correlated to the formation of intermediate phase with relatively lower melting point.</span><span style="font-family: 'Times New Roman', serif; font-size: 10pt; text-align: justify; text-indent: 36pt;"> </span></p>
<p style="text-align: justify;"><span style="font-size: 10.0pt; font-family: 'Times New Roman','serif'; mso-fareast-font-family: 'Times New Roman'; mso-ansi-language: EN-US; mso-fareast-language: EN-US; mso-bidi-language: AR-SA;" lang="EN-US">Finally, optimized (Ag<sub>1-<em>x</em></sub>Cu<em><sub>x</sub></em>)<sub>2</sub>ZnSnS­<sub>4</sub> thin films were incorporated in a PV device that resulted in a short circuit current density <em>J</em><sub>sc </sub></span><span style="font-size: 10.0pt; font-family: 'Times New Roman','serif'; mso-fareast-font-family: 'Times New Roman'; mso-ansi-language: EN-US; mso-fareast-language: EN-US; mso-bidi-language: AR-SA;" lang="EN-US">of 9.47 mA/cm<sup>2</sup>, open circuit voltage (<em>V<sub>oc</sub></em>) of 600 mV, and a fill factor of 34 % leading to <em>ƞ </em>of 1.92 %. </span></p>