Revealing the origin of voltage loss in mixed-halide perovskite solar cells,Energy & Environmental Science

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Revealing the origin of voltage loss in mixed-halide perovskite solar cells
Energy & Environmental Science ( IF 32.4 ) Pub Date : 2019-11-26 , DOI: 10.1039/c9ee02162k
Suhas Mahesh _{1,

2,

3,

4} , James M. Ball _{1,

2,

3,

4} , Robert D. J. Oliver _{1,

2,

3,

4} , David P. McMeekin _{4,

5,

6,

7} , Pabitra K. Nayak _{1,

2,

3,

4} , Michael B. Johnston _{1,

2,

3,

4} , Henry J. Snaith _{1,

2,

3,

4}

Affiliation

The tunable bandgap of metal-halide perovskites has opened up the possibility of tandem solar cells with over 30% efficiency. Iodide–bromide (I–Br) mixed-halide perovskites are crucial to achieve the optimum bandgap for such tandems. However, when the Br content is increased to widen the bandgap, cells fail to deliver the expected increase in open-circuit voltage (V_OC). This loss in V_OC has been attributed to photo-induced halide segregation. Here, we combine Fourier transform photocurrent spectroscopy (FTPS) with detailed balance calculations to quantify the voltage loss resulting from halide segregation, thus providing a means to quantify the impact of the low bandgap iodide-rich phases on performance. Our results indicate that, contrary to popular belief, halide segregation is not the dominant V_OC loss mechanism in Br-rich wide bandgap cells. Rather, the loss is dominated by the relatively low initial radiative efficiency of the cells, which arises from both imperfections within the absorber layer, and at the perovskite/charge extraction layer heterojunctions. We thus identify that focussing on maximising the initial radiative efficiency of the mixed-halide films and devices is more important than attempting to suppress halide segregation. Our results suggest that a V_OC of up to 1.33 V is within reach for a 1.77 eV bandgap perovskite, even if halide segregation cannot be suppressed.

中文翻译：

揭示混合卤化物钙钛矿太阳能电池中电压损失的根源

金属卤化物钙钛矿的可调节带隙开辟了串联太阳能电池效率超过30％的可能性。碘化物-溴化物（I-Br）混合卤化物钙钛矿对于实现此类双极膜的最佳带隙至关重要。但是，当增加Br含量以扩大带隙时，电池无法提供预期的开路电压（V _OC）的增加。V _OC的损失归因于光致卤化物的偏析。在这里，我们将傅里叶变换光电流能谱（FTPS）与详细的平衡计算相结合，以量化由卤化物偏析导致的电压损失，从而提供一种量化低带隙富碘化物相对性能的影响的方法。我们的结果表明，与普遍的看法相反，卤化物的偏析不是主要的挥发性_{有机化合物。}富Br的宽带隙细胞中的蛋白丢失机制。相反，损耗主要由电池的相对较低的初始辐射效率决定，该效率是由吸收层内以及钙钛矿/电荷提取层异质结处的缺陷引起的。因此，我们发现，重点放在最大化混合卤化物薄膜和器件的初始辐射效率上比尝试抑制卤化物偏析更为重要。我们的研究结果表明，一个V _OC高达1.33的V是伸手可及为1.77电子伏特的带隙的钙钛矿，即使卤化物偏析不能被抑制。

更新日期：2019-11-26

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