In this paper, a new method is proposed to trap sunlight in the active layer of thin film solar cells. In the proposed technique, multi-scale photonic topological insulators (PTI) realized by photonic crystals, are integrated inside the active layer of a thin film solar cell in order to trap sunlight in the cell. The trapping is realized by excitation of edge states supported by the designed topological insulator. The performance of the proposed solar cell with the topological insulator inside is investigated through full wave numerical analysis. Numerical results show that the proposed method enhances the absorption of the solar spectrum inside the cell in a wide range of wavelengths, and also for different angles of incidence. The short circuit current provided by the proposed solar cell is numerically calculated illustrating a value of 27.72 for a normally incident light which is 47% higher than a simple solar cell without topological insulator inside.