Sn precursor enables 12.4%efficient kesterite solar cell from DMSO solution with open circuit voltage deficit below 0.30 V

全面积效率12.4%、开路电压损失低于0.30 V的CZTSSe太阳能电池:Sn^4+前驱体在DMSO溶液中的使用

The limiting factor preventing further performance improvement of the kesterite(sulfide Cu2ZnSnS4(CZTS),selenide Cu2ZnSnS4(CZTSe),and their alloying Cu2Zn Sn(S,Se)4(CZTSSe))thin film solar cells is the large open-circuit voltage deficit(Voc,def)issue,which is 0.345 V for the current world record device with an efficiency of 12.6%.In this study,SnCl4 and Sn Cl2·2H2O were respectively used as tin precursor to investigate the Voc,def issue of dimethyl sulfoxide(DMSO)solution processed CZTSSe solar cells.Different complexations of tin compounds with thiourea(Tu)and DMSO resulted in different reaction pathways from the solution to the absorber material and thus dramatic differences in photovoltaic performance.The coordination of Sn^2+with Tu led to the formation of SnS,ZnS and Cu2S in the precursor film,which converted to selenides first and then fused to CZTSSe,resulting in poor film quality and device performance.The highest efficiency obtained from this film was 8.84%with a Voc,def of 0.391 V.The coordination of Sn4+with DMSO facilitated direct formation of CZTS phase in the precursor film which directly converted to CZTSSe during selenization,resulting in compositional uniform absorber and high device performance.A device with an active area efficiency of 12.2%and a Voc,def of 0.344 V was achieved from the Sn^4+solution processed absorber.Furthermore,CZTSSe/Cd S heterojunction heat treatment(JHT)significantly improved the performance of the Sn^4+device but had slightly negative effect on the Sn2+device.A champion CZTSSe solar cell with a total area efficiency of 12.4%(active area efficiency of 13.6%)and a low Voc,def of 0.297 V was achieved from the Sn^4+solution.Our results demonstrate the preformed uniform CZTSSe phase enabled by Sn4+precursor is the key for the highly efficient CZTSSe absorber.The lowest Voc,def and high efficiency achieved here shines new light on the future of CZTSSe solar cell.

开路电压损失(Voc,def)大是制约锌黄锡矿结构CZTSSe太阳能电池效率的关键因素,目前世界纪录效率(12.6%)CZTSSe电池的Voc,def为0.345 V.本文分别以SnCl4和SnCl2·2H2O为锡前驱体研究二甲基亚砜(DMSO)溶液法制备的CZTSSe太阳能电池的开路电压损失问题.研究发现不同价态的锡前驱体化合物与有机配体硫脲(Tu)和溶剂DMSO发生不同的配位反应,使得从溶液到CZTSSe吸光层薄膜的反应路径截然不同.Sn^2+与Tu配位导致前驱体薄膜中SnS、ZnS和Cu2S的生成,这些硫化物在硒化过程中首先转化成硒化物而后逐步熔合生成CZTSSe,其反应路径中多物相的转化和熔合导致薄膜光电性能差,由该薄膜获得的最优器件有效面积效率仅为8.84%,Voc,def为0.391 V.而Sn^4+与DMSO配位,该前驱体溶液经退火直接得到组成均匀的CZTS前驱体薄膜,在硒化过程中CZTS直接发生取代反应生成CZTSSe,得到的CZTSSe薄膜组成均匀,光电性能优异,由该薄膜制备的器件有效面积效率达到12.2%,Voc,def降低至0.344 V.此外,CZTSSe薄膜性质的不同导致CZTSSe/CdS异质结热处理(JHT)结果的不同.JHT显著提高了Sn4+器件的性能,却略微降低了Sn^2+器件的性能.最终,由Sn4+溶液获得了全面积效率为12.4%,有效面积效率高达13.6%,Voc,def低至0.297 V的CZTSSe太阳能电池器件.研究结果表明通过控制溶液中化学组成获得组成均匀的CZTS预制膜是获得高效CZTSSe电池薄膜材料和降低器件Voc,def的关键.本报道不仅为进一步提高CZTSSe电池效率提供了新的思路,而且实现了Voc,def首次低于0.30 V,预示了CZTSSe未来的应用前景.