Numerical simulation of graphene/Ag₂ZnSnSe₄ induced p-n junction solar cell

Abstract

Ag<sub>2</sub>ZnSnSe<sub>4</sub> is an n-type semiconductor with a suitable bandgap of 1.4 eV. In the present study, a graphene/Ag<sub>2</sub>ZnSnSe<sub>4</sub> induced p-n junction thin film solar cell is proposed and the physical mechanism and performance influencing factors of the solar cell are simulated and analyzed by using the wxAMPS software. The simulation results show that when a high work function graphene contacts an n-type Ag<sub>2</sub>ZnSnSe<sub>4</sub> semiconductor, the energy band of the Ag<sub>2</sub>ZnSnSe<sub>4</sub> absorber layer bends upward, meanwhile a p-type Ag<sub>2</sub>ZnSnSe<sub>4</sub> inversion layer is induced on the surface of n-type Ag<sub>2</sub>ZnSnSe<sub>4</sub>, therefore the p-type Ag<sub>2</sub>ZnSnSe<sub>4</sub> and n-type Ag<sub>2</sub>ZnSnSe<sub>4</sub> form an induced p-n homojunction. It is found that the work function of graphene and back contact significantly influence the photogenerated carrier separation, transportation and collection. The graphene work function should be 5.5 eV and the work function of back contact should not be greater than 4.4 eV, which is beneficial to the improving of the device performance. The doping concentration of Ag<sub>2</sub>ZnSnSe<sub>4</sub> absorber mainly affects the short-circuit current of the device, however, the defect density of Ag<sub>2</sub>ZnSnSe<sub>4</sub> absorber affects the whole device performance. When the work function of graphene and back contact are 5.5 eV and 3.8 eV, the doping concentration and defect density of Ag<sub>2</sub>ZnSnSe<sub>4</sub> absorber are 10<sup>16</sup> cm<sup>–3</sup> and 10<sup>14</sup> cm<sup>–33</sup>, respectively, the conversion efficiency of the graphene/Ag<sub>2</sub>ZnSnSe<sub>4</sub> induced p-n junction thin film solar cell can reach 23.42%. These simulation results provide the idea and physical explanation for designing a novel type of solar cell with high efficiency and low cost.

Numerical simulation of germanium selenide heterojunction solar cell

“…本文数值模拟采用的是微电子与光电子器件 模拟软件wxAMPS, 该软件基于求解载流子连续 性方程和泊松方程 [17] , 从而获得器件的能带结构, 载流子复合率, 量子效率以及太阳电池性能参数 (包括开路电压V oc 、短路电路J sc 、填充因子FF、 转换效率η)等. 图1显示了模拟所采用的器件结 构, 其中FTO是前电极, TiO 2 是太阳电池的ETL, GeSe是吸收层, Cu 2 O是HTL.…”

“…影响异质结太阳电池性能的因素包括了各功 能层材料的材料特性和利用功能层构筑的器件 结构. 本文构筑了结构为FTO/TiO 2 /GeSe/Cu 2 O/ Metal的太阳电池, 基于应用广泛的太阳电池模拟 软件wxAMPS [16][17][18][19] 对器件性能进行模拟研究, 以 期分析器件工作原理和预测太阳电池性能表现. 本 文没有采用CdS或者SnO 2 , 而是采用TiO 2 作为 电子输运层(electron transport layer, ETL), 这是 因为TiO 2 化学稳定性好、安全无毒, 并且TiO 2 和GeSe之间的导带带阶为+0.17 eV, 这种尖峰状 的能带排列不会影响光生电子从吸收层经由ETL 输运到前电极并进行收集, 但能降低载流子在界面 处的复合 [20] .…”