It is been widely reported that plasmonic effects in metallic nanomaterials can enhance light trapping in organix solar cells (OSCs). However, typical nanoparticles (NP) of high quality (i.e., mono-dispersive) only possess a single resonant absorption peak, which inevitably limits the power conversion efficiency (PCE) enhancement to a narrow spectral range. Broadband plasmonic absorption is obviously highly desirable. In this paper, a combination of Ag nanomaterials of different shapes, including nanoparticles and nanoprisms, is proposed for this purpose. The nanomaterials are synthesized using a simple wet chemical method. Theoretical and experimental studies show that the origin of the observed PCE enhancement is the simultaneous excitation of many plasmonic low- and high-order resonances modes, which are material-, shape-, size-, and polarization-dependent. Particularly for the Ag nanoprisms studied here, the high-order resonances result in higher contribution than low-order resonances to the absorption enhancement of OSCs through an improved overlap with the active material absorption spectrum. With the incorporation of the mixed nanomaterials into the active layer, a wide-band absorption improvement is demonstrated and the short-circuit photocurrent density (Jsc) improves by 17.91%. Finally, PCE is enhanced by 19.44% as compared to pre-optimized control OSCs. These results suggest a new approach to achieve higher overall enhancement through improving broadband absorption.