Hoke Eric T, Slotcavage Daniel J, Dohner Emma R, Bowring Andrea R, Karunadasa Hemamala I, McGehee Michael D
Department of Materials Science and Engineering , Stanford University , 476 Lomita Mall , Stanford , California 94305 , USA . Email:
Department of Chemistry , Stanford University , 337 Campus Drive , Stanford , California 94305 , USA . Email:
Chem Sci. 2015 Jan 1;6(1):613-617. doi: 10.1039/c4sc03141e. Epub 2014 Nov 4.
We report on reversible, light-induced transformations in (CHNH)Pb(Br I ). Photoluminescence (PL) spectra of these perovskites develop a new, red-shifted peak at 1.68 eV that grows in intensity under constant, 1-sun illumination in less than a minute. This is accompanied by an increase in sub-bandgap absorption at ∼1.7 eV, indicating the formation of luminescent trap states. Light soaking causes a splitting of X-ray diffraction (XRD) peaks, suggesting segregation into two crystalline phases. Surprisingly, these photo-induced changes are fully reversible; the XRD patterns and the PL and absorption spectra revert to their initial states after the materials are left for a few minutes in the dark. We speculate that photoexcitation may cause halide segregation into iodide-rich minority and bromide-enriched majority domains, the former acting as a recombination center trap. This instability may limit achievable voltages from some mixed-halide perovskite solar cells and could have implications for the photostability of halide perovskites used in optoelectronics.
我们报道了(CHNH)Pb(Br I )中的可逆光诱导转变。这些钙钛矿的光致发光（PL）光谱在1.68 eV处出现一个新的红移峰，在1个太阳常数光照下，该峰强度在不到一分钟内增强。这伴随着在~1.7 eV处子带隙吸收的增加，表明形成了发光陷阱态。光浸泡导致X射线衍射（XRD）峰分裂，表明分离成两个晶相。令人惊讶的是，这些光诱导变化是完全可逆的；在材料在黑暗中放置几分钟后，XRD图谱以及PL和吸收光谱恢复到初始状态。我们推测光激发可能导致卤化物分离成富含碘化物的少数域和富含溴化物的多数域，前者作为复合中心陷阱。这种不稳定性可能会限制一些混合卤化物钙钛矿太阳能电池可实现的电压，并可能对用于光电子学的卤化物钙钛矿的光稳定性产生影响。
