Controllable Growth of Perovskite Films by Room-Temperature Air Exposure for Efficient Planar Heterojunction Photovoltaic Cells

• Published in: Angewandte Chemie (International ed.) 2015-12, Vol.54 (49), p.14862-14865
• Main Authors: Yang, Bin, Dyck, Ondrej, Poplawsky, Jonathan, Keum, Jong, Das, Sanjib, Puretzky, Alexander, Aytug, Tolga, Joshi, Pooran C., Rouleau, Christopher M., Duscher, Gerd, Geohegan, David B., Xiao, Kai
• Format: Article
• Language: English
• Subjects: Air exposure; Air temperature; Annealing; Crystal defects; Crystal structure; Crystallinity; Degree of crystallinity; Diffusion layers; Diffusion length; Heat treatment; Heterojunctions; Interdiffusion; in situ X-ray diffraction; Performance degradation; Perovskites; Photovoltaic cells; photovoltaic devices; Photovoltaics; Radioactivity; Room temperature; SOLAR ENERGY; Temperature; thin films
• ISSN: 1433-7851; 1521-3773
• DOI: 10.1002/anie.201505882

A two‐step solution processing approach has been established to grow void‐free perovskite films for low‐cost high‐performance planar heterojunction photovoltaic devices. A high‐temperature thermal annealing treatment was applied to drive the diffusion of CH3NH3I precursor molecules into a compact PbI2 layer to form perovskite films. However, thermal annealing for extended periods led to degraded device performance owing to the defects generated by decomposition of perovskite into PbI2. A controllable layer‐by‐layer spin‐coating method was used to grow “bilayer” CH3NH3I/PbI2 films, and then drive the interdiffusion between PbI2 and CH3NH3I layers by a simple air exposure at room temperature for making well‐oriented, highly crystalline perovskite films without thermal annealing. This high degree of crystallinity resulted in a carrier diffusion length of ca. 800 nm and a high device efficiency of 15.6 %, which is comparable to values reported for thermally annealed perovskite films. A breath of fresh air: Simple room‐temperature air exposure can drive the interdiffusion between perovskite precursor layers and crystallize the perovskite thin films. The obtained perovskite films show high crystallinity and well‐aligned orientation. The devices with and without a TiO2 electron transporting layer yielded high efficiencies of 15.6 % and 13.8 %, respectively.