Surface treatment using large alkyl/aryl ammonium cations has demonstrated reduced open-circuit voltage (V OC ) deficits in perovskite solar cells (PSCs), but the origin of the improvements has been vaguely attributed to defect passivation. Here, we combine microscopic probing of the local electrical properties, thermal admittance spectroscopic analysis, and firstprinciples calculations to elucidate the critical role of arylammonium interface layers in suppressing ion migration in wide-bandgap (WBG) PSCs. Our results reveal that arylammonium surface treatment using phenethylammonium iodide increases the activation energy barrier for ion migration on the surface, which suppresses the accumulation of charge defects at surface and grain boundaries, leading to a reduced dark saturation current density in WBG PSCs. With device optimization, our champion 1.73 eV PSC delivers a power conversion efficiency of 19.07% with a V OC of 1.25 V, achieving a V OC deficit of 0.48 V.
Dopant‐free hole transport materials (HTMs) are essential for commercialization of perovskite solar cells (PSCs). However, power conversion efficiencies (PCEs) of the state‐of‐the‐art PSCs with small molecule dopant‐free HTMs are below 20%. Herein, a simple dithieno[3,2‐b:2′,3′‐d]pyrrol‐cored small molecule, DTP‐C6Th, is reported as a promising dopant‐free HTM. Compared with commonly used spiro‐OMeTAD, DTP‐C6Th exhibits a similar energy level, a better hole mobility of 4.18 × 10−4 cm2 V−1 s−1, and more efficient hole extraction, enabling efficient and stable PSCs with a dopant‐free HTM. With the addition of an ultrathin poly(methyl methacrylate) passivation layer and properly tuning the composition of the perovskite absorber layer, a champion PCE of 21.04% is achieved, which is the highest value for small molecule dopant‐free HTM based PSCs to date. Additionally, PSCs using the DTP‐C6Th HTM exhibit significantly improved long‐term stability compared with the conventional cells with the metal additive doped spiro‐OMeTAD HTM. Therefore, this work provides a new candidate and effective device engineering strategy for achieving high PCEs with dopant‐free HTMs.
Organic p‐type semiconductors with tunable structures offer great opportunities for hybrid perovskite solar cells (PVSCs). We report herein two dithieno[3,2‐b:2′,3′‐d]pyrrole (DTP) cored molecular semiconductors prepared through π‐conjugation extension and an N‐alkylation strategy. The as‐prepared conjugated molecules exhibit a highest occupied molecular orbital (HOMO) level of −4.82 eV and a hole mobility up to 2.16×10−4 cm2 V−1 s−1. Together with excellent film‐forming and over 99 % photoluminescence quenching efficiency on perovskite, the DTP based semiconductors work efficiently as hole‐transporting materials (HTMs) for n‐i‐p structured PVSCs. Their dopant‐free MA0.7FA0.3PbI2.85Br0.15 devices exhibit a power conversion efficiency over 20 %, representing one of the highest values for un‐doped molecular HTMs based PVSCs. This work demonstrates the great potential of using a DTP core in designing efficient semiconductors for dopant‐free PVSCs.
Comparing
to the traditional CdS buffer layer, zinc magnesium oxide
(ZMO) offers the following advantages for CdTe-based thin-film solar
cells: it introduces a spike to conduction band offset, which reduces
interface recombination that is beneficial for increasing open-circuit
voltage (V
OC) and decreases parasitic
optical absorption of the buffer layer that is favorable for enhancing
short-circuit current (J
SC). However,
ZMO/CdTe thin-film solar cells often show the so-called S-kink behavior
in their current–voltage curves, making it difficult to reproduce
the expected benefits. Here, we show that S-kink can be successfully
eliminated, and improved V
OC and J
SC can be simultaneously achieved if the CdCl2 treatment process is conducted in oxygen-free atmosphere.
As a result, the device efficiencies increased from 9.2% to 16.1%.
Our device characterizations and simulations reveal that a sufficiently
high electron density of the ZMO buffer layer is critical to eliminate
the S-kink, which is achievable through an oxygen-free CdCl2 treatment.
An appropriately combined triple interface modification, i.e., post-annealing, O2-plasma, and KCl treatments, is employed to ameliorate the optoelectronic properties of sputtered NiOx films and achieve better device performance.
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