大剩余极化强度窄带隙无机钙钛矿铁电薄膜及铁电退极化场与P-N结内建电场协同增强激子分离型太阳能电池探究

Although CuInS2 thin-film solar cells have high photo-generated current, their open-circuit voltage is low; The open-circuit voltage of ferroelectric photovoltaic devices is very high, but the short-circuit current is quite small. In this project, we plan to design [KbNO3]1-x [BaNi1/2Nb1/2O3-δ]x (KBNNO) based ferroelectric thin films with large remnant polarization and narrow band gap and introduce it into the P-N junction of CuInS2 solar cells to build thin-film solar cells involving ferroelectric depolarization and P-N junction built-in electric fields. The introduction of KBNNO ferroelectric thin film can increase visible-light-absorbing ability and the jointly function of both ferroelectric depolarization and P-N junction electric fields enhances greatly the separation of photo-generated exciton and carrier transport ability and thus high photovoltaic conversion efficiency is expected. The relationship of chemical composition with the band-gap, the position of valance band and conduction band of KBNNO are simulated, and the microcosmic nature of influencing the band gap is revealed; KBNNO thin film with suitable band-gap and high optical absorption coefficient is prepared by pulsed laser deposition technique and the quantitative relationships of the thickness, composition and the band-gap, optical absorption coefficient are constructed. The preparing technology of multilayer film and the compositions of KBNNO thin film are adjusted to obtain good matching between CuInS2/KBNNO and KBNNO/ZnO interfaces in crystal lattice and electronic band structures，and at last developing CuInS2/KBNNO/ZnO tandem solar cells with high photoelectric conversion efficiency.

CuInS2薄膜电池具有大的光生电流，开路电压却受限于其带隙；铁电光伏器件开路电压可很高，短路电流却很小。本项目拟设计出大剩余极化强度窄带隙的铌酸钾-铌镍酸（KBNNO）基铁电薄膜，并将其引入CuInS2电池P-N结中构筑新型铁电退极化场和P-N结内建电场协同增强型薄膜电池。KBNNO铁电层的插入可增加可见光子吸收，而两场叠加协同作用能增强光生激子分离和提高载流子输运，从而可望获得高光电转换效率。通过模拟成分与KBNNO禁带宽度、价带及导带能级间关系，揭示影响带隙的微观机制；采用脉冲激光沉积法制备带隙合适、剩余极化强度大的KBNNO薄膜，构建薄膜厚度、成分与带隙和吸光系数间定量关系。通过多层膜制备工艺控制和KBNNO薄膜组分调整，实现CuInS2/KBNNO和KBNNO/ZnO界面处薄膜晶格结构和电子能带结构的优化配置，最终制备出高光电转换效率CuInS2/KBNNO/ZnO级联电池。

传统p-n结太阳能电池具有大的光生电流，开路电压却受限于其带隙；铁电光伏器件开路电压可很高，短路电流却很小。因此，可以将铁电材料引入传统太阳能电池p-n结中利用铁电退极化电场和p-n结内建电场的协同作用促进光生载流子分离，从而实现传统p-n结太阳能电池效率的进一步提升。本项目设计出大剩余极化强度窄带隙的铌酸钾-铌镍酸（KBNNO）基铁电薄膜，系统研究了沉积氧压对其结构、成分、形貌、铁电性能和光学带隙等的影响。揭示了影响KBNNO薄膜带隙的内在因素，并构建出了禁带宽度与剩余极化强度与Ni含量的定量关系。通过传统固相法开发出KNN基大极化窄带隙铁电材料，研究了掺杂元素对其结构、形貌、铁电性能、光学性能及光伏性能的影响。构建出基于铁电/半导体异质结的光电器件，对异质结界面的微结构、电子能带结构进行了深入研究，阐明了铁电退极化场对器件光伏性能及光探性能的调控机制。设计并制备出基于铁电-CIGS化合物半导体的铁电退极化场与p-n结内建电场协同增强激子分离型太阳能电池，其认证光电转换效率达到13.86%，为新型高效太阳能电池的制备提供了新思路。为能进一步提高太阳能电池效率，我们还制备了几种常用太阳能电池窗口层材料ZnO，SnO2以及Ga2O3，并研究了它们的晶体结构和光学性能。成功实现了基于这些氧化物半导体薄膜的紫外光电探测器的制备，并对探测器的结构、光学、光电响应特性进行了研究。这些结果有望促进ZnO，SnO2以及Ga2O3在紫外光电探测器方面的实际应用。