Fakharuddin Azhar, Seybold Michael, Agresti Antonio, Pescetelli Sara, Matteocci Fabio, Haider Muhammad Irfan, Birkhold Susanne T, Hu Hao, Giridharagopal Rajiv, Sultan Muhammad, Mora-Seró Iván, Di Carlo Aldo, Schmidt-Mende Lukas
Department of Physics , University of Konstanz , D-78457 Konstanz , Germany.
IMEC Kapeldreef 75 , Heverlee 3001 , Belgium.
ACS Appl Mater Interfaces. 2018 Dec 12;10(49):42542-42551. doi: 10.1021/acsami.8b18200. Epub 2018 Nov 29.
Solar cells based on organic-inorganic halide perovskites are now leading the photovoltaic technologies because of their high power conversion efficiency. Recently, there have been debates on the microstructure-related defects in metal halide perovskites (grain size, grain boundaries, etc.) and a widespread view is that large grains are a prerequisite to suppress nonradiative recombination and improve photovoltaic performance, although opinions against it also exist. Herein, we employ blends of methylammonium lead iodide perovskites with an insulating polymer (polyvinylpyrrolidone) that offer the possibility to tune the grain size in order to obtain a fundamental understanding of the photoresponse at the microscopic level. We provide, for the first time, spatially resolved details of the microstructures in such blend systems via Raman mapping, light beam-induced current imaging, and conductive atomic force microscopy. Although the polymer blend systems systematically alter the morphology by creating small grains (more grain boundaries), they reduce nonradiative recombination within the film and enhance its spatial homogeneity of radiative recombination. We attribute this to a reduction in the density of bulk trap states, as evidenced by an order of magnitude higher photoluminescence intensity and a significantly higher open-circuit voltage when the polymer is incorporated into the perovskite films. The solar cells employing blend systems also show nearly hysteresis-free power conversion efficiency ∼17.5%, as well as a remarkable shelf-life stability over 100 days.
基于有机-无机卤化物钙钛矿的太阳能电池因其高功率转换效率而引领着光伏技术的发展。最近，关于金属卤化物钙钛矿中与微观结构相关的缺陷（晶粒尺寸、晶界等）存在诸多争论，一种普遍的观点是大晶粒是抑制非辐射复合并提高光伏性能的先决条件，尽管也存在反对意见。在此，我们采用甲基碘化铅钙钛矿与绝缘聚合物（聚乙烯吡咯烷酮）的混合物，这种混合物提供了调节晶粒尺寸的可能性，以便在微观层面上对光响应有基本的了解。我们首次通过拉曼映射、光束诱导电流成像和导电原子力显微镜提供了此类混合体系中微观结构的空间分辨细节。尽管聚合物混合体系通过产生小晶粒（更多晶界）系统性地改变了形态，但它们减少了薄膜内的非辐射复合并增强了其辐射复合的空间均匀性。我们将此归因于体陷阱态密度的降低，当聚合物掺入钙钛矿薄膜时，光致发光强度提高了一个数量级以及开路电压显著更高就证明了这一点。采用混合体系的太阳能电池还显示出几乎无滞后的功率转换效率约为17.5%，以及超过100天的显著保质期稳定性。
