First-Principles Study on Influences of Crystal Structure and Orientation on Band Offsets at the CdS/Cu2ZnSnS4Interface

Wujisiguleng Bao,Masaya Ichimura

doi:10.1155/2012/619812

Wujisiguleng Bao, Masaya Ichimura

Open Access

https://doi.org/10.1155/2012/619812

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Abstract

Cu<sub >2</sub>ZnSnS<sub >4</sub> (CZTS) has attracted much attention recently as an absorber layer material in a heterojunction solar cell. Using the first-principles method, we calculate the band offsets for the CdS/CZTS heterojunction. The valence band offset <svg style="vertical-align:-3.3907pt;width:28.1px;" id="M1" height="15.65" version="1.1" viewBox="0 0 28.1 15.65" width="28.1" xmlns:xlink="http://www.w3.org/1999/xlink" xmlns="http://www.w3.org/2000/svg"> <g transform="matrix(.017,-0,0,-.017,.062,11.362)"><path id="x394" d="M600 0h-557v24l268 633l28 8l261 -641v-24zM497 50l-194 489l-196 -489h390z" /></g><g transform="matrix(.017,-0,0,-.017,10.959,11.362)"><path id="x1D438" d="M609 650l-19 -162l-30 -2q2 69 -14 94q-9 18 -28.5 26t-74.5 8h-88q-30 0 -37 -6.5t-12 -36.5l-41 -212h103q48 0 69 5.5t32 19t26 50.5h29l-40 -198h-30q2 58 -11.5 70.5t-85.5 12.5h-99l-30 -167q-17 -87 3 -101q18 -15 111 -15q59 0 89 7t54 27q8 7 15.5 16t16 21.5
l14 20.5t15 23.5t13.5 21.5l29 -10q-52 -129 -71 -163h-500l6 28q66 4 83 17.5t28 73.5l77 409q11 61 -0.5 75.5t-78.5 18.5l10 28h467z" /></g> <g transform="matrix(.012,-0,0,-.012,21.7,15.45)"><path id="x1D463" d="M457 332q0 -81 -41 -161.5t-105.5 -131.5t-129.5 -51q-46 0 -79 30.5t-33 86.5q0 18 7 51q18 95 46 187q6 19 6 33q0 7 -7 7q-24 0 -78 -64l-20 23q32 48 73 77t78 29q33 0 33 -46q0 -38 -10 -70q-28 -92 -39 -152q-7 -38 -7 -57q0 -78 69 -78q68 0 118 75.5t50 194.5
q0 43 -12 57q-11 12 -11 24q0 19 15 35.5t34 16.5q18 0 30.5 -34.5t12.5 -81.5z" /></g> </svg> is 1.2 eV for the (001) CdS/CZTS heterointerface and 1.0 eV for the (010) heterointerface, when CZTS is considered to crystallize in the kesterite structure. When CZTS is considered to crystallize in the stannite structure, <svg style="vertical-align:-3.3907pt;width:67.712502px;" id="M2" height="15.65" version="1.1" viewBox="0 0 67.712502 15.65" width="67.712502" xmlns:xlink="http://www.w3.org/1999/xlink" xmlns="http://www.w3.org/2000/svg"> <g transform="matrix(.017,-0,0,-.017,.062,11.362)"><use xlink:href="#x394"/></g><g transform="matrix(.017,-0,0,-.017,10.959,11.362)"><use xlink:href="#x1D438"/></g> <g transform="matrix(.012,-0,0,-.012,21.7,15.45)"><use xlink:href="#x1D463"/></g> <g transform="matrix(.017,-0,0,-.017,32.762,11.362)"><path id="x3D" d="M535 323h-483v50h483v-50zM535 138h-483v50h483v-50z" /></g><g transform="matrix(.017,-0,0,-.017,47.449,11.362)"><path id="x31" d="M384 0h-275v27q67 5 81.5 18.5t14.5 68.5v385q0 38 -7.5 47.5t-40.5 10.5l-48 2v24q85 15 178 52v-521q0 -55 14.5 -68.5t82.5 -18.5v-27z" /></g><g transform="matrix(.017,-0,0,-.017,55.609,11.362)"><path id="x2E" d="M113 -12q-24 0 -39.5 16t-15.5 42q0 24 16 40.5t40 16.5t40 -16.5t16 -40.5q0 -26 -16 -42t-41 -16z" /></g><g transform="matrix(.017,-0,0,-.017,59.485,11.362)"><use xlink:href="#x31"/></g> </svg> eV for the (001) heterointerface and <svg style="vertical-align:-3.3907pt;width:67.712502px;" id="M3" height="15.65" version="1.1" viewBox="0 0 67.712502 15.65" width="67.712502" xmlns:xlink="http://www.w3.org/1999/xlink" xmlns="http://www.w3.org/2000/svg"> <g transform="matrix(.017,-0,0,-.017,.062,11.362)"><use xlink:href="#x394"/></g><g transform="matrix(.017,-0,0,-.017,10.959,11.362)"><use xlink:href="#x1D438"/></g> <g transform="matrix(.012,-0,0,-.012,21.7,15.45)"><use xlink:href="#x1D463"/></g> <g transform="matrix(.017,-0,0,-.017,32.762,11.362)"><use xlink:href="#x3D"/></g><g transform="matrix(.017,-0,0,-.017,47.449,11.362)"><use xlink:href="#x31"/></g><g transform="matrix(.017,-0,0,-.017,55.609,11.362)"><use xlink:href="#x2E"/></g><g transform="matrix(.017,-0,0,-.017,59.485,11.362)"><path id="x33" d="M285 378v-2q65 -13 102 -54.5t37 -97.5q0 -57 -30.5 -104.5t-74 -75t-85.5 -42t-72 -14.5q-31 0 -59.5 11t-40.5 23q-19 18 -16 36q1 16 23 33q13 10 24 0q58 -51 124 -51q55 0 88 40t33 112q0 64 -39 96.5t-88 32.5q-29 0 -64 -11l-6 29q77 25 118 57.5t41 84.5
q0 45 -26.5 69.5t-68.5 24.5q-67 0 -120 -79l-20 20l43 63q51 56 127 56h1q66 0 107 -37t41 -95q0 -42 -31 -71q-22 -23 -68 -54z" /></g> </svg> eV for the (010) heterointerface. In any case, the conduction band minimum of CZTS is higher than that of CdS, and the conduction band offset <svg style="vertical-align:-3.3907pt;width:27.2125px;" id="M4" height="15.65" version="1.1" viewBox="0 0 27.2125 15.65" width="27.2125" xmlns:xlink="http://www.w3.org/1999/xlink" xmlns="http://www.w3.org/2000/svg"> <g transform="matrix(.017,-0,0,-.017,.062,11.362)"><use xlink:href="#x394"/></g><g transform="matrix(.017,-0,0,-.017,10.959,11.362)"><use xlink:href="#x1D438"/></g> <g transform="matrix(.012,-0,0,-.012,21.7,15.45)"><path id="x1D450" d="M383 397q0 -32 -35 -49q-12 -6 -23 8q-37 45 -84 45t-90 -71q-40 -65 -40 -167q0 -57 22 -86t59 -29q38 0 81.5 24.5t69.5 51.5l16 -21q-44 -53 -104 -84t-109 -31q-56 0 -89.5 41t-33.5 117q0 61 30 124t79 105q33 28 81 50.5t86 22.5q34 0 59 -15.5t25 -35.5z" /></g> </svg> is in a range between 0.1 and 0.4 eV.

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