Numerical optimization and performance evaluation of ZnPC:PC70BM based dye-sensitized solar cell

DFT and TD-DFT Investigations for the Limitations of Lengthening the Polyene Bridge between N,N-dimethylanilino Donor and Dicyanovinyl Acceptor Molecules as a D-π-A Dye-Sensitized Solar Cell

One useful technique for increasing the efficiency of organic dye-sensitized solar cells (DSSCs) is to extend the π-conjugated bridges between the donor (D) and the acceptor (A) units. The present study used the DFT and TD-DFT techniques to investigate the effect of lengthening the polyene bridge between the donor N, N-dimethyl-anilino and the acceptor dicyanovinyl. The results of the calculated key properties were not all in line with expectations. Planar structure was associated with increasing the π-conjugation linker, implying efficient electron transfer from the donor to the acceptor. A smaller energy gap, greater oscillator strength values, and red-shifted electronic absorption were also observed when the number of polyene units was increased. However, some results indicated that the potential of the stated dyes to operate as effective dye-sensitized solar cells is limited when the polyene bridge is extended. Increasing the polyene units causes the HOMO level to rise until it exceeds the redox potential of the electrolyte, which delays regeneration and impedes the electron transport cycle from being completed. As the number of conjugated units increases, the terminal lobes of HOMO and LUMO continue to shrink, which affects the ease of intramolecular charge transfer within the dyes. Smaller polyene chain lengths yielded the most favorable results when evaluating the efficiency of electron injection and regeneration. This means that the charge transfer mechanism between the conduction band of the semiconductor and the electrolyte is not improved by extending the polyene bridge. The open circuit voltage (VOC) was reduced from 1.23 to 0.70 V. Similarly, the excited-state duration (τ) decreased from 1.71 to 1.23 ns as the number of polyene units increased from n = 1 to n = 10. These findings are incompatible with the power conversion efficiency requirements of DSSCs. Therefore, the elongation of the polyene bridge in such D-π-A configurations rules out its application in solar cell devices.

Highly efficient emerging Ag2BaTiSe4 solar cells using a new class of alkaline earth metal-based chalcogenide buffers alternative to CdS

Cu2ZnSn(S,Se)4 is a non-toxic, earth-abundant photovoltaic absorber. However, its efficiency is limited by a large open circuit voltage (VOC) deficit occurring due to its antisite defects and improper band alignment with toxic CdS buffer. Therefore, finding an absorber and non-toxic buffers that reduce VOC deficit is crucial. Herein, for the first time, Ag2BaTiSe4 is proposed as an alternative absorber using SCAPS-1D wherein a new class of alkaline earth metal chalcogenide such as MgS, CaS, SrS, and BaS is applied as buffers, and their characteristics are compared with CdS to identify their potential and suitability. The buffer and absorber properties are elucidated by tuning their thickness, carrier concentration, and defect density. Interestingly, optimization of the buffer's carrier concentration suppressed the barrier height and accumulation of charge carriers at the absorber/buffer interface, leading to efficiencies of 18.81%, 17.17%, 20.6%, 20.85%, 20.08% in MgS, CaS, SrS, BaS, and CdS-based solar cells respectively. Upon optimizing Ag2BaTiSe4, MoSe2, and interface defects maximum efficiency of > 28% is achieved with less VOC loss (~ 0.3 V) in all solar cells at absorber's thickness, carrier concentration, and defect density of 1 µm, 1018 cm-3, 1015 cm-3 respectively, underscoring the promising nature of Ag2BaTiSe4 absorber and new alkaline earth metal chalcogenide buffers in photovoltaics.