The utilization of an inorganic hole-transport layer (HTL) is one of the most effective methods to improve the stability and reduce the cost of perovskite solar cells (PSCs). However, achieving high-quality inorganic HTL films, especially HTL films in n-i-p structures, via solution processes remains a big challenge. Here, a simple surface modification strategy for low-cost and stable cuprous oxide (Cu2O) quantum dots is proposed, which utilizes a silane coupling agent. The modified Cu2O can be directly deposited on the perovskite film as the top HTL without decomposing the perovskite to maintain an n-i-p structure. The efficiency (18.9%) of PSCs with surface-modified Cu2O as the HTL is significantly higher than that (11.9%) of PSCs with unmodified Cu2O, which is also the record efficiency for a Cu2O-based perovskite solar cell in n-i-p structure. The enhanced performance of PSCs is attributed to the remarkably enhanced film properties achieved through surface modification. Moreover, because of the dopant-free technology and hydrophobic surface, the Cu2O-based PSCs have distinctly better stability than 2,2',7,7'-tetrakis[N,N-di(4-methoxyphenyl)amino]-9,9'-spiro-bifluorene-based PSCs.