of these devices is combined with high temperature chemical vapor deposition, which makes it incompatible with roll-to-roll processing. Other emerging second generation solar cells are thin film chalcogenides like CIGS (CuInGaSe 2 ) and CdTe, which show terrestrial cell efficiency of 20.3% and 16.5% respectively [6, 7] . The scarcity, cost and toxicity associated with In, Ga, and Cd elements present in these cells limit their sustainability in the future. Thus wide spread applications of solar

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... ells will require dramatic decrease in cost through the use of non-toxic, inexpensive, and earth-abundant materials. The drawbacks in the present PV materials motivate us to look for alternatives. Due to the low absorption cross section, crystalline silicon requires thick layers, which will increase costs. Amorphous silicon (a-Si) has a higher absorption cross section and low processing cost compared to its crystalline counterpart, but it has stability problems. GaAs based solar cells have high efficiency, but the arsenic toxicity and the substrate cost limit their use. CIGS thin film solar cells show promise if the scarce and costly indium and gallium could be replaced by other elements. The quaternary compound semiconductor CZTS (Cu 2 ZnSnS 4 ) [8] possesses promising characteristic optical properties; band-gap energy of about 1.5 eV and large absorption coefficient in the order of 10 4 cm −1 . The highly efficient CdTe solar cell is promising, but has obstacles such as cadmium toxicity, tellurium scarcity, and cost. While the results of research and commercialization of crystalline Si, GaAs, CIGS, CdTe, etc. cells are commendable, a search for alternative materials is indispensable and necessary to achieve low cost, light weight, and low toxicity arrays.