Fabrication and Optimization of CdSe Solar Cells for Possible Top Cell of Silicon‐Based Tandem Devices

Abstract

commercial modules, respectively), excellent stability (>25 years guaranteed lifetime), low cost (<$0.30 per peak watt), and mature production lines. [1] Further improving power conversion efficiency (PCE) is the most effective way to reduce the cost of solar electricity. Nevertheless, the record PCE of single-junction Si solar cells is approaching its theoretical limit of 29.4%. [2] Tandem solar cells are widely regarded as the most promising strategy to break the Shockley-Queisser (S-Q) efficiency limit [3] since they can reduce the thermal relaxation energy loss of highenergy photons. [4] Theoretical calculations show that in double-junction Si-based tandem solar cells, the top cells should have a ≈1.7 eV bandgap (E g ) and tandem solar cells could achieve an efficiency limit of ≈45% [5] (Figure 1a).At present, III-V compounds and halide perovskites with a 1.7 eV bandgap are the most promising top cells for Si-based tandem solar cells (Figure 1a). [1b] Both of their single-junction and Si-based tandem solar cells have achieved >20% and >29% efficiency, respectively. [6] Nevertheless, they both suffer from obvious drawbacks. III-V photovoltaics are stable and highly efficient; however, they require sophisticated fabrication procedures and expensive fabrication equipment, leading to the prohibitive cost (≈$150 per peak watt) [7] and limited deployment. As for halide perovskites, they could be directly processed, either via solution processing or thermal evaporation, onto Si bottom solar cells without sacrificing device performance. Currently, two-terminal perovskite/Si tandem solar cells have achieved a record efficiency of 29.8%, but the long-term stability of perovskite top cells is not fully resolved. [8] Overall, what is the best choice as the top cell for Si-based tandem devices is still an open question in the field. It is thus highly valuable to explore new absorber materials for the top cell.Various semiconductors with ≈1.7 eV bandgap, such as amorphous-Si (a-Si), Zn x Cd 1-x Te, CuGaSe 2, and Sb 2 S 3 , have been considered as the alternative top cells over the past years (Table 1). A-Si sounds promising in terms of the simple chemical element, low fabrication cost, and large absorption coefficient. In 1990, an impressive efficiency of 15.04% has been achieved for two-terminal a-Si/c-Si tandem solar cells, but no progress was made since then due to its complex defects and the band tail state effect. [9] Wide bandgap Zn x Cd 1-x Te and CuGaSe 2 , originating from the commercial CdTe and Cu(In,Ga)Se 2 solar cells, Silicon-based tandem solar cells are regarded as one of the most feasible ways to break the single-junction Shockley-Queisser limit efficiency and further reduce the cost of solar electricity. Recently, wide-bandgap (≈1.7 eV) perovskite solar cells have drawn intense research interest as the top cell for Si-based tandem devices. Despite significant progress in device efficiency, the unsatisfactory stability of perovskites is still a huge concern. Besides halide perovskites, there are many in...

A Codoping Strategy for Efficient Planar Heterojunction Sb2S3 Solar Cells

“…Furthermore, the energy levels of E F , valance band maximum (VBM), and conduction band minimum (CBM) of the control thin film were determined utilizing ultraviolet photoelectron spectroscopy (UPS). The corresponding values of the control film were estimated [ 17 ] as −4.26, −5.27, and −3.56 eV (Figure S4, Supporting Information). Then the energy diagram of the Sb 2 S 3 SCs could be plotted as shown in the inset of Figure S4d (Supporting Information).…”

Improved Carrier Lifetimes of CdSe Thin Film via Te Doping for Photovoltaic Application

“…Researches on CdSe thin-film solar cells can be traced back to the 1980s but has been stagnant for nearly three decades without significant research progress. − Most studies of CdSe solar cells have mainly focused on the fabrication methods and post-treatment of CdSe thin films. , The recorded efficiency of laboratory-scale CdSe solar cells is only 6.0%, significantly lower than the theoretical Shockley-Queisser limit of 28%. Recently, we also achieved a high power conversion efficiency (PCE) of 6% in CdSe solar cells . The low open-circuit voltage ( V OC ) of 0.58 V is only 40% of the theoretical value, becoming the main factor limiting the performance.…”

“…Among these defects, bulk defects are considered to be one of the key factors that determined the quality of CdSe thin films and the performance of photovoltaic devices. The quasi-Fermi level splitting calculations according to Würfel’s generalized Planck law also show that the bulk defect in CdSe thin films brings a 0.353 V V OC loss. , Thus, an in-depth understanding and passivation of bulk phase defects in CdSe thin films are essential to enhancing the device performance, but little research has been done on these.…”

“…This qualitatively explains why the carrier lifetime in CdTe is much longer than the reported CdSe because the deep levels within the band gap can serve as a nonradiative recombination center. Indeed, the existence of deep defects in CdSe leads to a short carrier lifetime (<200 ps) in CdSe thin films . Therefore, it is important to passivate the V Se defect and enhance the carrier lifetime for the performance improvement of CdSe solar cells.…”

Emergence of flexible kesterite solar cells: progress and perspectives

“…Provided that the e ciency of CZTS solar cells can be enhanced to a more commercially acceptable level (>15%), the commercialization pathway will become clearer. On the other hand, as the urge to develop high-e ciency and low-cost tandem PV technologies is more and more appreciated, [20][21][22] exible low bandgap CZTSSe has a great opportunity to be integrated into all-thin-lm exible tandem technologies as one of the few promising low-cost thin-lm bottom cells. 20 Low bandgap CZTSSe, especially pure-selenide CZTSe, has an optimal bandgap of ~1.0 eV required for the bottom cell of a two-junction tandem.…”