Impact of oxygen incorporation on interface optimization and defect suppression for efficiency enhancement in Cu_(2)ZnSn(S,Se)_(4)solar cells

Kesterite Cu_(2)ZnSn(S,Se)_(4)(CZTSSe)solar cells suffer from severe carrier recombination,limiting the photovoltaic performance.Unfavorable energy band alignment at the p-n junction and defective front interface are two main causes.Herein,oxygen incorporation in CZTSSe via absorber air-annealing was developed as a strategy to optimize its surface photoelectric property and reduce the defects.With optimized oxygen incorporation conditions,the carrier separation and collection behavior at the front interface of the device is improved.In particular,it is found that oxygen incorporated absorber exhibits increased band bending,larger depletion region width,and suppressed absorber defects.These indicate the dynamic factors for carrier separation become stronger.Meanwhile,the increased potential difference between grain boundaries and intra grains combined with the decreased concentration of interface deep level defect in the absorber provide a better path for carrier transport.As a consequence,the champion efficiency of CZTSSe solar cells has been improved from 9.74%to 12.04%with significantly improved open-circuit voltage after optimized air-annealing condition.This work provides a new insight for interface engineering to improve the photoelectric conversion efficiency of CZTSSe devices.

Defect suppression and energy level alignment in formamidinium-based perovskite solar cells

The vast majority of high-performance perovskite solar cells(PSCs) are based on a formamidinium lead iodide(FAPbI_(3))-dominant composition. Nevertheless, the FA-based perovskite films suffer from undesirable phase transition and defects-induced non-ideal interfacial recombination, which significantly induces energy loss and hinders the improvement of device performance. Herein, we employed 4-fluorophenylmethylammonium iodide(F-PMAI) to modulate surface structure and energy level alignment of the FA-based perovskite films. The superior optoelectronic films were obtained with reduced trap density, pure α-phase FAPbI_(3) and favorable energy band bending. The lifetime of photogenerated charge carriers increased from 489.3 ns to 1010.6 ns, and a more “p-type” perovskite film was obtained by the post-treatment with F-PMAI. Following this strategy, we demonstrated an improved power conversion efficiency of 22.59% for the FA-based PSCs with an open-circuit voltage loss of 399 m V.

Interface optimization and defects suppression via Na F introduction enable efficient flexible Sb_(2)Se_(3) thin-film solar cells

Sb_(2)Se_(3) with unique one-dimensional(1D) crystal structure exhibits exceptional deformation tolerance,demonstrating great application potential in flexible devices.However,the power conversion efficiency(PCE) of flexible Sb_(2)Se_(3) photovoltaic devices is temporarily limited by the complicated intrinsic defects and the undesirable contact interfaces.Herein,a high-quality Sb_(2)Se_(3) absorber layer with large crystal grains and benign [hkl] growth orientation can be first prepared on a Mo foil substrate.Then NaF intermediate layer is introduced between Mo and Sb_(2)Se_(3),which can further optimize the growth of Sb_(2)Se_(3)thin film.Moreover,positive Na ion diffusion enables it to dramatically lower barrier height at the back contact interface and passivate harmful defects at both bulk and heterojunction.As a result,the champion substrate structured Mo-foil/Mo/NaF/Sb_(2)Se_(3)/CdS/ITO/Ag flexible thin-film solar cell delivers an obviously higher efficiency of 8.03% and a record open-circuit voltage(V_(OC)) of 0.492 V.This flexible Sb_(2)Se_(3) device also exhibits excellent stability and flexibility to stand large bending radius and multiple bending times,as well as superior weak light photo-response with derived efficiency of 12.60%.This work presents an effective strategy to enhance the flexible Sb_(2)Se_(3) device performance and expand its potential photovoltaic applications.

Defect suppression mechanism of ultrasonic vibration-assisted drilling carbon fiber/bismaleimide composite

Ultrasonic vibration-assisted drilling(UVAD)has recently been successfully applied in the drilling of carbon fiber reinforced polymer/plastic(CFRP)due to its high reliability.Multiple defects have been observed in the CFRP drilling process which negatively affects the quality of the hole.The carbon fiber/bismaleimide(BMI)composites is an advanced kind of CFRPs with greater strength and heat resistance,having been rapidly applied in lightweight and high temperature resistant structures in the aerospace field.To suppress the defect during the drilling of carbon fiber/BMI composites,it is necessary to comprehensively understand the defect formation and suppression mechanism at different positions.In this study,the defects formation in both conventional drilling(CD)and UVAD were observed and analyzed.The variation trend in the defect factor and thrust force with the spindle speed and feed rate were acquired.The results revealed that the UVAD could significantly enhance the hole’s quality with no delamination and burr.Meanwhile,the defect suppression mechanism and thrust force in UVAD were analyzed and verified,where the method of rod chip removal affected the exit defect formation.In summary,UVAD can be considered a promising and competitive technique for drilling carbon fiber/BMI composites.

Regulation of Zn/Sn ratio in kesterite absorbers to boost 10% efficiency of Cu_2ZnSn(S,Se)_4 solar cells

The Zn/Sn ratio in Cu2ZnSn（S, Se）4 （CZTSSe） films has been regulated to control the composition-related phase, defect, and photoelectric properties for high performance kesterite solar cells. It is found that the increase in the Zn/Sn ratio can slightly narrow the energy band gap to extend the light absorption range and improve the photocurrent. Optimal Zn/Sn ratio of 1.39 in CZTSSe film is obtained with the least secondary phase, the lowest defect density, and the longest charge recombination lifetime. Up to 10.1% photoelectric conversion efficiency has been achieved by this composition regulation.