We reveal a new approach for forming a Ag-graded absorber to overcome the large open-circuit voltage deficit in (Cu,Ag)2ZnSn(S,Se)4 solar cells.

In this article, pure phase metastable wurtzite Cu 2 ZnSnS 4 (CZTS) nanocrystals (NCs) were synthesized by a facile one-pot method. When pure 1dodecanethiol (DDT) was used as the solvent, two coexisting CZTS phases (wurtzite and kesterite) were found. When an increased amount of oleylamine (OAm) was added to DDT, kesterite CZTS disappeared gradually, and the asobtained CZTS NCs became smaller and more uniform. When 0.5 mL of OAm was added, rice-like pure phase metastable wurtzite CZTS NCs were obtained. The factors, including amount of OAm, reaction temperature, reaction time, and concentration of precursors, which influence the morphology, size, and monodispersity of CZTS NCs, were studied in detail. The results showed OAm played an important role in the formation of the final pure phase metastable wurtzite NCs. Time-dependent experiments were performed to observe the growth of CZTS NCs. The final CZTS NCs evolved from spherical-like Cu 2 S NCs through rhombuslike intermediate shaped NCs to rice-like pure wurtzite CZTS NCs. On the basis of the detailed time-dependent shape and elemental composition evolutions, a possible asynchronous doping growth and formation mechanism was proposed. The optical and electrical properties of the pure wurtzite CZTS NCs were also investigated. The band gap of the rice-like CZTS is about 1.49 eV, which approaches the optimum value for solar photoelectric conversion. Meanwhile, the current−voltage characteristics and Hall effect measurement of the wurtzite CZTS NCs films indicated that rice-like CZTS NCs favored the electronic transmission and thus may induce the generation of photocurrent. Thus, the obtained wurtzite CZTS NCs are more suitable for using as absorber layer in low cost solar cells.

The partial substitution of Cu with Ag into the host lattice of CuZnSn(S,Se) thin films can reduce the open-circuit voltage deficit (V) of CuZnSn(S,Se) (CZTSSe) solar cells. In this paper, elemental Cu, Ag, Zn, Sn, S, and Se powders were dissolved in solvent mixture of 1,2-ethanedithiol (edtH) and 1,2-ethylenediamine (en) and used for the formation of (CuAg)ZnSn(S,Se) (CAZTSSe) thin films with different Ag/(Ag + Cu) ratios. The key feature of this approach is that the impurity atoms can be absolutely excluded. Further results indicate that the variations of grain size, band gap, and depletion width of the CAZTSSe layer are generally determined by Ag substitution content. Benefiting from the V enhancement (∼50 mV), the power conversion efficiency is successfully increased from 7.39% (x = 0) to 10.36% (x = 3%), which is the highest efficiency of Ag substituted devices so far.

Cu­(In,Ga)­Se2 (CIGS) is considered a promising photovoltaics material due to its excellent properties and high efficiency. However, the complicated deep defects (such as InCu or GaCu) in the CIGS layer hamper the development of polycrystalline CIGS solar cells. Numerous efforts have been employed to passivate these defects which distributed in the grain boundary and the CIGS/CdS interface. In this work, we implemented an effective Ag substituting approach to passivate bulk defects in CIGS absorber. The composition and phase characterizations revealed that Ag was successfully incorporated in the CIGS lattice. The substituting of Ag could boost the crystallization without obviously changing the band gap. The C–V and EIS results demonstrated that the device showed enlarged Wd and beneficial carrier transport dynamics after Ag incorporation. The DLTS result revealed that the deep InCu defect density was dramatically decreased after Ag substituting for Cu. A champion Ag-substituted CIGS device exhibited a remarkable efficiency of 15.82%, with improved V OC of 630 mV, J SC of 34.44 mA/cm2, and FF of 72.90%. Comparing with the efficiency of an unsubstituted CIGS device (12.18%), a Ag-substituted CIGS device exhibited 30% enhancement.

Although the rapid development of polymer solar cells (PSCs) has been achieved, it is still a great challenge to explore efficient ways for improving power conversion efficiency (PCE) of PSCs from materials and device engineering. Ternary strategy has been confirmed as an efficient way to improve PCE of PSCs by employing three kinds of materials. In this work, one polymer donor PM6, and two non‐fullerene materials N3 and MF1 are selected to prepare ternary PSCs with layer‐by‐layer (LbL) or bulk‐heterojunction (BHJ) structure. The LbL and BHJ‐PSCs exhibit PCEs of 16.75% and 16.76% with 15 wt% MF1 content in acceptors, corresponding to over 5% or 4% PCE improvement compared with N3‐based binary PSCs with LbL or BHJ structure. The PCE improvement is mainly attributed to the fill factor enhancement from 73.29% to 76.95% for LbL‐PSCs or from 74.13% to 77.51% for BHJ‐PSCs by employing the ternary strategy. This work indicates that ternary strategy has great potential in preparing highly efficient LbL‐PSCs via simultaneously optimizing molecular arrangement and the thickness of each layer.