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Spectroscopic and electrical signatures of acceptor states in solution processed Cu2ZnSn(S,Se)4 solar cells
Journal of Materials Chemistry C ( IF 5.7 ) Pub Date : 2017-10-25 00:00:00 , DOI: 10.1039/c7tc03953k
Devendra Tiwari 1, 2, 3, 4 , Ekaterina Skidchenko 4, 5, 6, 7, 8 , Jake W. Bowers 9, 10, 11, 12, 13 , Michael V. Yakushev 4, 5, 6, 7, 8 , Robert W. Martin 4, 5, 6, 7, 8 , David J. Fermin 1, 2, 3, 4
Affiliation  

The nature and dynamics of acceptor states in solution-processed Cu2ZnSn(S,Se)4 (CZTSSe) thin films are investigated by variable temperature photoluminescence (PL) and electrical impedance spectroscopy. Highly pure I-4 phase CZTSSe with the composition Cu1.6ZnSn0.9(S0.23Se0.77)4 is synthesized by sequentially spin coating of dimethyl-formamide/isopropanol solutions containing metal salts and thiourea onto Mo coated glass, followed by annealing in an Se atmosphere at 540 °C. As-annealed films are highly compact with a thickness of 1.3 μm and grain sizes above 800 nm, with a band gap of 1.18 eV. Photovoltaic devices of 0.25 cm2 with the architecture glass/Mo/CZTSSe/CdS/i-ZnO/Al:ZnO demonstrate a power conversion efficiency reaching up to 5.7% in the absence of an anti-reflective coating. Under AM 1.5G illumination at 296 K, the best device shows a 396 mV open-circuit voltage (VOC), 27.8 mA cm−2 short-circuit current (JSC) and 52% fill factor (FF). The overall dispersion of these parameters is under 15% for a total of 20 devices. In the near IR region, PL spectra are dominated by two broad and asymmetrical bands at 1.14 eV (PL1) and 0.95 eV (PL2) with characteristic power and temperature dependences. Analysis of the device electrical impedance spectra also reveals two electron acceptor states with the same activation energy as those observed by PL. This allows assigning PL1 as a radiative recombination at localized copper vacancies (VCu), while PL2 is associated with CuZn antisites, broadened by potential fluctuations (band tails). The impact of these states on device performance as well as other parameters, such as barrier collection heights introduced by partial selenization of the back contact, are discussed.

中文翻译:

溶液处理的Cu 2 ZnSn(S,Se)4太阳能电池中受体态的光谱和电学特征

通过可变温度光致发光(PL)和电阻抗光谱技术研究了固溶处理的Cu 2 ZnSn(S,Se)4(CZTSSe)薄膜中受体态的性质和动力学。通过依次将含有金属盐和硫脲的二甲基甲酰胺/异丙醇溶液旋涂到涂Mo的玻璃上,然后在Se中退火,可以合成出具有Cu 1.6 ZnSn 0.9(S 0.23 Se 0.774组成的高纯度I-4相CZTSSe。气氛在540°C。退火后的薄膜高度致密,厚度为1.3μm,晶粒尺寸大于800 nm,带隙为1.18 eV。0.25 cm 2的光伏设备使用建筑玻璃/ Mo / CZTSSe / CdS / i-ZnO / Al:ZnO的情况下,在没有抗反射涂层的情况下,功率转换效率高达5.7%。在296 K的AM 1.5G照度下,最佳器件显示396 mV的开路电压(V OC),27.8 mA cm -2的短路电流(J SC)和52%填充系数(FF)。对于总共20个设备,这些参数的总分散度低于15%。在近红外区域,PL光谱主要由两个宽且不对称的波段控制,分别在1.14 eV(PL1)和0.95 eV(PL2)处,并具有特定的功率和温度依赖性。器件电阻抗谱的分析还揭示了两个电子受体状态,其活化能与PL观察到的状态相同。这允许将PL1指定为局部铜空位(V Cu)的辐射复合,而PL2与Cu Zn相关联反位点,由潜在的波动(带尾)加宽。讨论了这些状态对器件性能以及其他参数(例如,由于背接触的部分硒化而引入的势垒收集高度)的影响。
更新日期:2017-11-17
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