[10a-PB3-1~14] 13.9 Compound solar cells

▲ [10a-PB3-5] Investigation of performance limiting key parameters in CuIn_1-xGa_xSe₂ photocathodes

Vikas Nandal¹, 〇Kazuhiko Seki¹, Hiroyuki Kobayashi², Kazunari Domen² (1.AIST, 2.Tokyo Univ.)

Keywords:semiconductor, Chalcogenide Compound

With the advancement of cost-effective fabrication processes and improvement in solar cell efficiencies beyond 22%, CuIn_1-xGa_xSe (CIGS) materials have attracted immense research focus towards the development of photocathodes for production of hydrogen gas by light induced water splitting process. However, the recently published reports indicated that the efficiency loss for such photocatalytic activity as compared to solar cells is quite significant. Therefore, it is imperative to understand different loss pathways to identify key parameters for performance optimization of such devices. In this context, we performed optoelectrical simulations to study the effect of interface defect density N_I(at CIGS/CdS), Ga composition (or mole fraction x), bulk deep defect density N_B, and electron surface recombination velocity S_non the performance of CIGS/CdS based photocathodes. Interestingly, we find that (a) at low N_Ithe onset potential (V_onset) is governed by bulk defects N_Bwhich increase linearly with mole fraction x, however, the high interface defects density N_Ilimits and saturates V_onsetfor high mole fraction x as shown in Fig.1 (right frame): supported by experimental data of photocathodes and solar cells, (b) the bulk defect density N_Baffects the optimum range of mole fraction x and decrease the maximum achievable efficiency for low N_I, and (c) the surface reaction between electrons and protons and hence S_nplays significant role in limiting the maximum achievable efficiency for photocathodes as evident from Fig.1 (right frame). Our results are of broad interest with its immediate relevance for photocatalytic and photovoltaic research community.