Perovskite solar cells have attracted great attention in recent years due to its advantageous features including low production cost, ease of fabrication and rapidly-improving device efficiencies. Research activities have been mainly devoted to the development of new manufacturing processes, materials, device structures and better stability. There is little research on the fundamentals of solar spectrum absorption in the device layers and almost no attempts have been made to optically improve the weak absorption of perovskite materials in infrared (IR) bands. Using a full-wave simulation approach, we report for the first time the contributions of each device layers in light absorptions across the whole solar spectrum. It is found that perovskite layer dominants the absorption in UV and visible bands, while the electrode layers dominants the IR bands. In order to optically enhance the light absorption in perovskite layer in IR band, we propose to use closely-spaced plasmonic nanoparticle array to achieve considerable optical absorption in the IR band, which haven't been investigated in the literature. The concept is to use plasmonics to create hot spots in active layers, which can considerably enhance the localized light absorption in perovskite material via light-flow-circulating and nonlinear absorption mechanisms. Under optimized conditions, a 58.2% IR-band absorption enhancement has been achieved in this study. This work provides a new path towards achieving higher efficiency perovskite solar cells