In n^+ (p^+)-p(n) [X(x)≡GaP_(1-x) Sb_x]-alloy junction solar cells at T=300 K, 0≤x≤1, by basing on the same physical model and the same treatment method, as those used in our recent works [1, 2], we will also investigate the maximal efficiencies, η_(Imax.(IImax.)), obtained at the open circuit voltage V_oc (=V_(ocI(ocII))), according to highest hot reservoir temperatures, T_H (K), obtained from the Carnot efficiency theorem, which was demonstrated by the use of the entropy law. In the present work, some concluding remarks are given in the following.(1) In the heavily doped emitter region, the effective density of electrons (holes), N^*, given in parabolic conduction (valence) bands, expressed as functions of the total dense impurity density, N, donor (acceptor)-radius, r_(d(a)), and x-concentration, is defined in Eq. (9d), as: N^* 〖(N,r〗_(d(a)),x)〖≡N-N〗_CDn(NDp) 〖(r〗_(d(a)),x), where N_CDn(NDp) is the Mott critical density in the metal-insulator transition, determined in Eq. (9a). Then, we have showed that (i) the origin of such the Mott’s criterium, Eq. (9a), is exactly obtained from the reduced effective Wigner-Seitz radius r_(sn(sp)), characteristic of interactions, as given in Equations (9b, 9c), and further (ii) N_(CDn(CDp)) is just the density of electrons (holes) localized in the exponential conduction (valence)-band tail (EBT), as that demonstrated in [1]. (2) In Table 3n, for the n^+-p GaP_(1-x) 〖Sb〗_x-alloy junction solar cell and for r_(Sn(Cd))-radius, one obtains with increasing x=(0, 0.5, 1): η_(Imax.) (↘)= 32.83 %, 29.58 %, 23.77 %, according to T_H (↘)=446.6 K,426.0 K,393.5 K, at V_ocI=1.06 V,1.06 V,1.29 V, respectively.(3) In Table 5p, for the p^+-n GaP_(1-x) 〖Sb〗_x-alloy junction solar cell and for r_(Cd(Sn))-radius, one obtains with increasing x=(0, 0.5, 1): η_(IImax.) (↗)= 32.41 %, 34.32 %, 35.19 %, according to T_H (↗)=443.8 K,456.8 K,462.9 K, at V_ocII (V)[>V_ocI (V)]=1.17 V,1.25 V,1.44 V, respectively, suggesting that such η_(Imax.(IImax.))-and-T_H variations depend on V_ocII (V)[>V_ocI (V)]-ones.