Top Limit Characteristics of Cascade Tunnel Structure Silicon PCs

A new type homogeneous planar photoelectric converter (PC) on the basis of multijunction semiconductor n+-p-p+(t)n+-p-p+(t)…(t)n+-p-p+ tunnel silicon structure has been investigated. The entire structure is a cascade PC consisting of a number of elements of the structure – single PCs connected in series by tunnel layers (t) with thickness δ and illuminated by light that has consistently passed through the previous semiconductor layers. The theory of converter of both monochromatic and solar radiation has been developed and the top limit values of their photoelectric and power characteristics have been determined, including the optimal thickness and number of single PCs layered on a base PC, their spectral sensitivity, current-voltage characteristics and efficiency.The optimal thickness of single PC decreases with the number of elements N in the cascade.The open-circuit voltage grows practically linearly with N for small δ and medium N values. Non-linearity increases with δ reaching maximum for certain value Nm, and then decreases exponentially for further increasing of N.Efficiency increases non-monotonously, as well, passes a flat maximum in the range of medium N and then falls near exponentially for large values of number N.For the optimal number the higher efficiency limit reaches its maximum that in the range Nm ∼ 5-7 exceeds considerably that of the base PC, particularly in the range of low charge carriers collection efficiency of the base PC.