Department of Chemistry and RASEI, University of Colorado, Boulder, Colorado 80309, USA.
Materials and Chemical Sciences and Technology Directorate, National Renewable Energy Laboratory, Golden, Colorado 80409, USA.
J Chem Phys. 2019 Sep 21;151(11):114111. doi: 10.1063/1.5102095.
Photoelectrochemical (PEC) water splitting is one of the most important approaches being investigated for solar fuel generation. In this study, we determine the maximum thermodynamic power conversion efficiencies (PCEs) of PEC water splitting two-bandgap tandem devices that produce multiple carriers per photon absorbed via Multiple Exciton Generation (MEG) or Singlet Fission (SF) and in the presence of solar concentration. Here, we employ a detailed balance thermodynamic analysis to determine the effects of top cell thickness, solar concentration, carrier multiplication, electrode overvoltage (V), and water absorption on PEC power conversion efficiency for water splitting cells. We have found a maximum PEC power conversion efficiency of 62.9% in cells using two ideal tandem MEG absorbers with bandgaps of 0.3 and 1.2 eV at 1000-suns solar concentration and 0 overvoltage; the maximum PCE for two tandem SF absorbers under the same conditions is nearly the same at 59% with the same values for the absorption thresholds. A very interesting and important result was that, upon thinning the top cell, the range of viable bandgaps for both the top and bottom cells is extended by as much as 0.5-1 eV while still maintaining high maximum conversion efficiency (60-63%). The effects of imposing different solar concentrations from 1X to 1000X and having different tandem configurations of SF and MEG layers were also studied.
光电化学 (PEC) 水分解是最受关注的太阳能燃料生成方法之一。在这项研究中，我们确定了通过多激子产生 (MEG) 或单线态裂变 (SF) 吸收单个光子产生多个载流子的两能带隙串联器件的最大热力学功率转换效率 (PCE)，并考虑了太阳能浓缩的情况。在这里，我们采用详细平衡热力学分析来确定顶电池厚度、太阳能浓缩、载流子倍增、电极过电压 (V) 和水吸收对水分解电池 PEC 功率转换效率的影响。我们发现，在 1000 倍太阳光浓度和 0 过电压下，使用两个理想的 MEG 吸收器（带隙分别为 0.3 和 1.2 eV）的两能带隙串联 MEG 吸收器的最大 PEC 功率转换效率为 62.9%；在相同条件下，两个串联 SF 吸收器的最大 PCE 几乎相同，吸收阈值相同，为 59%。一个非常有趣和重要的结果是，通过减薄顶电池，顶电池和底电池的可行能带隙范围可以扩展多达 0.5-1 eV，同时仍然保持高的最大转换效率 (60-63%)。我们还研究了不同太阳能浓缩度（从 1X 到 1000X）和不同 SF 和 MEG 层串联配置的影响。
