As large‐area photon collection devices designed to convert sunlight into electricity, luminescent solar concentrators (LSCs) have been proposed for more than 40 years. In practical sunlight‐harvesting applications, existing glass windows or curtain walls have to be torn down and then replaced by traditional LSCs with planar optical waveguides, leading to high manufacture and installation costs. One alternative and attractive approach is to design and manufacture LSCs that are compatible with and can be attached directly onto the original building glass windows, which substantially reduces the overall costs. Herein, a feasible strategy of attachable transparent LSCs is proposed, converting ordinary glass to LSCs by simply attaching novel luminescent films. By integrating a phenylethylammonium (PEA)‐assisted perovskite−PVDF composite film with a polymer antireflection/barrier layer, as‐prepared composite films show dramatical improvement in photoluminescence quantum yield from 4.1% to 45.8% (11‐fold enhancement), substantially increased optical transmittance from 30.9% to 71.1% (at 700 nm), as well as strongly suppressed photoluminescence (PL) quenching during the attaching process. The fabricated attachable LSCs demonstrate a maximum optical efficiency of 2.8% at the geometric factor of 5 and retain 87% of initial optical efficiency after 2 months of storage in ambient conditions.