Rondiya Sachin R, Jadhav Yogesh, Dzade Nelson Y, Ahammed Raihan, Goswami Tanmay, De Sarkar Abir, Jadkar Sandesh, Haram Santosh, Ghosh Hirendra N
Institute of Nano Science and Technology, Mohali, Punjab 160062, India.
Department of Chemistry, Savitribai Phule Pune University, Pune 411007, India.
ACS Appl Energy Mater. 2020 Jun 22;3(6):5153-5162. doi: 10.1021/acsaem.9b02314. Epub 2020 May 5.
To improve the constraints of kesterite CuZnSnS (CZTS) solar cell, such as undesirable band alignment at p-n interfaces, bandgap tuning, and fast carrier recombination, cadmium (Cd) is introduced into CZTS nanocrystals forming CuZn Cd SnS through cost-effective solution-based method without postannealing or sulfurization treatments. A synergetic experimental-theoretical approach was employed to characterize and assess the optoelectronic properties of CuZn Cd SnS materials. Tunable direct band gap energy ranging from 1.51 to 1.03 eV with high absorption coefficient was demonstrated for the CuZn Cd SnS nanocrystals with changing Zn/Cd ratio. Such bandgap engineering in CuZn Cd SnS helps in effective carrier separation at interface. Ultrafast spectroscopy reveals a longer lifetime and efficient separation of photoexcited charge carriers in CuCdSnS (CCTS) nanocrystals compared to that of CZTS. We found that there exists a type-II staggered band alignment at the CZTS (CCTS)/CdS interface, from cyclic voltammetric (CV) measurements, corroborated by first-principles density functional theory (DFT) calculations, predicting smaller conduction band offset (CBO) at the CCTS/CdS interface as compared to the CZTS/CdS interface. These results point toward efficient separation of photoexcited carriers across the p-n junction in the ultrafast time scale and highlight a route to improve device performances.
为了改善硫铜锡锌矿（CZTS）太阳能电池的限制因素，如p-n界面处不理想的能带排列、带隙调节和快速载流子复合，通过经济高效的基于溶液的方法，在不进行后退火或硫化处理的情况下，将镉（Cd）引入CZTS纳米晶体中形成CuZnCdSnS。采用了实验与理论相结合的方法来表征和评估CuZnCdSnS材料的光电性能。对于具有不同Zn/Cd比的CuZnCdSnS纳米晶体，展示了可调的直接带隙能量范围为1.51至1.03 eV，且具有高吸收系数。CuZnCdSnS中的这种带隙工程有助于在界面处实现有效的载流子分离。超快光谱显示，与CZTS相比，CuCdSnS（CCTS）纳米晶体中光激发电荷载流子的寿命更长且分离效率更高。我们通过循环伏安法（CV）测量发现，在CZTS（CCTS）/CdS界面处存在II型交错能带排列，第一性原理密度泛函理论（DFT）计算也证实了这一点，预测与CZTS/CdS界面相比，CCTS/CdS界面处的导带偏移（CBO）更小。这些结果表明光激发载流子在超快时间尺度上能在p-n结处有效分离，并突出了一条改善器件性能的途径。
