Internal Encapsulation for Lead Halide Perovskite Films for Efficient and Very Stable Solar Cells

External encapsulation technique as a straightforward craft process has been adopted to prevent the infiltration of moisture and oxygen, thereby improving environmental stabilities of lead halide perovskite solar cells (PSCs). However, irreversible light-induced degradation originating from various vacancies and ion diffusion or migration inside the device cannot be efficiently solved by external encapsulation. Herein, an internal encapsulation strategy by introducing NbCl5 at the buried tin oxide/perovskite interface and spin-casting n-butylammonium bromide on top of perovskite is developed to comprehensively passivate the vacancies and hence block the channels for ion diffusion or migration. The internal encapsulation strategy results in better homogeneous electron transport layer and effective vacancy passivation at the buried interface and simultaneously generates a more homogeneous, better crystallized perovskite in the vertical direction with significantly reduced residual PbI2. Furthermore, fewer oxygen vacancies and formation of ultrathin Nb2O5 lead to a better interfacial energy level alignment for electron transfer. As a result, power conversion efficiency (PCE) of the resulting PSCs is as high as 24.01%. More importantly, the device demonstrates an excellent stability, retaining 88% of its initial PCE at its maximum power point tracking measurement (under 100 mW cm(-2) white light illumination at approximate to 55 degrees C temperature, in N-2 atmosphere) after 1000 h.

Automated summary

This study presents an internal encapsulation strategy to improve the stability and efficiency of lead halide perovskite solar cells. By introducing NbCl5 and n-butylammonium bromide, vacancies are effectively passivated and channels for ion diffusion or migration are blocked, resulting in better homogeneity of the electron transport layer and improved energy level alignment at the interface. Moreover, the residual PbI2 is significantly reduced. The resulting solar cells demonstrate a high power conversion efficiency of 24.01% and excellent stability, retaining 88% of the initial efficiency after 1000 hours of testing.