over 30% detailed balance limiting efficiency, as well as to its earth-abundant and environment-benign constituents. [1-3] The increase in power conversion efficiency to a record of 12.6% in the last decade has demonstrated the huge potential of these materials. [4,5] However, as one of the most complicated compound semiconductors, kesterite has much more intricate defect chemistry than its counterparts, Cu(In,Ga)Se 2 (CIGS) and CdTe, [6-8] making the control of intrinsic defects a major challenge. Deep intrinsic defects like Sn Zn antisites and related [Cu Zn +Sn Zn ] clusters act as deep recombination centers, leading to the short carrier lifetime. [7,9,10] Additionally, the large population of defect clusters like [2Cu Zn +Sn Zn ] introduces considerable potential (i.e., band or electrostatic) fluctuation. [11] Consequently, the performance of CZTSSe solar cells are currently stagnated by the large open-circuit voltage (V OC) deficit. [12,13] To address the detrimental intrinsic defects and defect clusters in CZTSSe absorber, multiple strategies have been employed. As suggested by the first-principle calculations, the formation energy of intrinsic defects and Kesterite-based Cu 2 ZnSn(S,Se) 4 semiconductors are emerging as promising materials for low-cost, environment-benign, and high-efficiency thin-film photo voltaics. However, the current state-of-the-art Cu 2 ZnSn(S,Se) 4 devices suffer from cation-disordering defects and defect clusters, which generally result in severe potential fluctuation, low minority carrier lifetime, and ultimately unsatisfactory performance. Herein, critical growth conditions are reported for obtaining high-quality Cu 2 ZnSnSe 4 absorber layers with the formation of detrimental intrinsic defects largely suppressed. By controlling the oxidation states of cations and modifying the local chemical composition, the local chemical environment is essentially modified during the synthesis of kesterite phase, thereby effectively suppressing detrimental intrinsic defects and activating desirable shallow acceptor Cu vacancies. Consequently, a confirmed 12.5% efficiency is demonstrated with a high V OC of 491 mV, which is the new record efficiency of pure-selenide Cu 2 ZnSnSe 4 cells with lowest V OC deficit in the kesterite family by E g /q-Voc. These encouraging results demonstrate an essential route to overcome the long-standing challenge of defect control in kesterite semiconductors, which may also be generally applicable to other multinary compound semiconductors.

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Kesterite Cu2ZnSnS4 is a promising photovoltaic material containing low‐cost, earth‐abundant, and stable semiconductor elements. However, the highest power conversion efficiency of thin‐film solar cells based on Cu2ZnSnS4 is only about 11% due to low open‐circuit voltage and fill factor mainly caused by antisite defects and unfavorable heterojunction interface. In this work, a postannealing procedure is proposed to complete a Cd‐alloyed Cu2ZnSnS4 device. The postannealing to complete the device significantly enhances the performance of the indium tin oxide and promotes the moderate interdiffusion of elements between the layers in the device. As a result of the diffusion of Cu, Zn, In, and Sn, the interfacial electron and hole densities are improved, leading to the achievement of a suitable band alignment for carrier transport. The postannealing also reduces the interface traps and deep‐level defects, contributing to decreased nonradiative recombination. Therefore, the open‐circuit voltage and fill factor are both improved, and an efficiency over 12% for pure sulfide‐based kesterite thin‐film solar cells is obtained.

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Shockley-Queisser (SQ) limits, mainly due to severe open-circuit voltage (V OC ) losses. Furthermore, the scarcity (In, Ga, and Te) and toxicity (Cd) of elements within the light-harvesting compounds might constrain their further employment for mass production. In recent years, more attention was paid to novel semiconducting materials, especially those made from low-toxicity and earth-abundant elements such as Sb 2 Se 3 , Cu 2 ZnSn(S,Se) 4 (CZTSSe), GeSe, and SnS. [2][3][4][5] Among them, antimony triselenide (Sb 2 Se 3 ) has been recognized as a very promising candidate for thin-film photovoltaics in the future. The constituent elements Sb and Se are both low-toxicity and earth-abundant, and hence makes the material suitable for sustainable development. Besides, Sb 2 Se 3 has excellent optoelectronic properties with an ideal bandgap (≈1.2 eV) and high absorption coefficient (>10 5 cm −1 ). [2] The material possesses a unique 1D crystal structure where (Sb 4 Se 6 ) n ribbons are covalently bonded in a tilted vertical orientation along which photogenerated carriers are able to travel readily. [2] On the other hand, carrier transport would become much more difficult in horizontal directions since the carriers have to hop between the (Sb 4 Se 6 ) n ribbons held by van der Waals forces, as demonstrated by Tang's group in 2015. [2] Due to the strong correlation between the grain orientation and the performance of Sb 2 Se 3 solar cell, since then, much effort has been put into the field of grain orientation control using various thin-film deposition techniques including thermal evaporation, vapor transport deposition (VTD), hydrothermal and sputtering. [6][7][8][9][10][11][12][13][14][15] Accordingly, the PCE of Sb 2 Se 3 solar cell has increased sharply from 2.1% to 7.6% in only a few years, which was mostly attributed to continuous breakthroughs of the short-circuit current density (J SC ) and fill factor (FF) of the device. Mai's group utilized close spaced sublimation (CSS) to prepare [001]-oriented Sb 2 Se 3 nanorods which substantially promote the carrier transport within the ribbons. [16] The champion device presented a record PCE of 9.2%, along with significant improved J SC of 32.58 mA cm −2 and FF of 70.3%, which are 83% and 110% higher than the corresponding parameters of the device with a 2.1% PCE respectively. [6] However, an open-circuit voltage (V OC ) of 0.4 V that only showed an 18% enhancement compared to that of the 2.1% PCE device, was still considered as the main bottleneck for the 9.2% champion device. Similarly, other state-of-the-art Sb 2 Se 3 solar cells also suffered from an unsatisfied V OC of about Despite the fact that antimony triselenide (Sb 2 Se 3 ) thin-film solar cells have undergone rapid development in recent years, the large open-circuit voltage (V OC ) deficit still remains as the biggest bottleneck, as even the world-record device suffers from a large V OC deficit of 0.59 V. Here, an effective interface engineering approach is reported where the Sb 2 Se 3 /CdS heterojunction (HTJ)...

The high cost and complex production technique restrict the use of the conventional thermoelectric generators. In this work, we demonstrate a promising flexible thin film thermoelectric generator using the N-type Al-doped ZnO and P-type Zn-Sb based thin film. By using the cost-effective zinc based thermoelectric materials and flexible substrate, we greatly reduce the cost production of thin film thermoelectric generator. The maximum output power of our device with 10 couples is 246.3 μW when the temperature difference is 180 K. The maximum output power of the flexible thin film thermoelectric generator produced per couple and per unit temperature difference was 0.14 μW per K-couple, which is about several times that of other thin film reported. The thin film thermoelectric generator with low cost and excellent output power was fabricated on flexible substrate, which is can be made into various shapes for micro- and nano-energy application.

Halide perovskites are one of the ideal photovoltaic materials for constructing flexible solar devices due to relatively high efficiencies for low‐temperature solution‐processed devices. However, the overwhelming majority of flexible perovskite solar cells are produced using spin coating, which represents a major hurdle for upscaling. Here, a scalable approach is reported to fabricate efficient and robust flexible perovskite solar cells on a polymer substrate. Thiourea is introduced into perovskite precursor solution to modulate the crystal growth, resulting in dense and uniform perovskite thin films on rough surfaces. As a decisive step, a cascade energy alignment is realized for the hole extraction layer by rationally designing a bilayer interface comprised of PEDOT:PSS/PTAA with a distinct offset in the highest occupied molecular orbital levels, enabling markedly enhanced charge extraction and spectral response. An efficiency as high as 19.41% and a record fill factor up to 81% are achieved for flexible perovskite devices processed by a scalable printing method. Equally important, the bilayer interface reinforces the bendability of the indium tin oxide substrate, leading to enhanced mechanical robustness of the flexible devices. These results underpin the importance of morphology control and interface design in constructing high‐performance flexible perovskite solar cells.