Solar Energy Conversion CIGS Solar Cell As one of thin film solar cell, Cu(InGa)(SeS)2 (CIGS) CIGS solar cells display a high optical absorption coeﬃcient, tunable band gap energy, long-term chemical stability, and a high eﬃciency. Over the past few years, various approaches have been explored for achieving high-quality CIGS absorber thin ﬁlms. Also, through molecular precursor solution methods and subsequent heating process, fabrication cost of CIGS cell could be decreased with enough high efficiency. Our group has fabricated cheap, stable and efficient CIGS thin film solar cell by combing nano structure and solution deposition method. Moreover, by patterning the film layer, CIGS cell could be developed in series solar cell supplying high potential. Quantum Dot Sensitized Solar Cell Quantum-dot-sensitized solar cells (QDSSCs) have attracted significant attention as next-generation solar cells given the characteristics of quantum dots, including tunable absorption, high-extinction coefficients, and size-dependent band gap energies. Moreover, multiple exciton generation (MEG) can further improve solar-cell efficiency. Theoretically, QDSSCs can achieve a maximum power conversion efficiency (PCE) of 44%. Although various types of QDs have been studied, including CdS, CdSe, PbS, PbSe, and CIGS. Perovskite Solar Cell Perovskite solar cells (PSCs) have attracted tremendous attention of researchers in the photovoltaic fields. Although the power conversion efficiency (PCE) of the PSC in the first report was 3.8%, the recent PCE of PSCs has been incredibly increased to 20.1% in the past few years. This outstanding advance of the PSC was possible on the basis of various advantages of the perovskite as a light absorber, such as the high light absorption coefficient, excellent charge-carrier mobilities for both electrons and holes, easily tunable band-gap energy, and various facile synthetic processes for the perovskites.